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Cryptophyte plastids originated from a red algal ancestor through secondary endosymbiosis. Cryptophyte photosystem I (PSI) associates with transmembrane alloxanthin-chlorophyll a/c proteins (ACPIs) as light-harvesting complexes (LHCs). Here, we report the structure of the photosynthetic PSI–ACPI supercomplex from the cryptophyte Chroomonas placoidea at 2.7-Å resolution obtained by crygenic electron microscopy. Cryptophyte PSI–ACPI represents a unique PSI–LHCI intermediate in the evolution from red algal to diatom PSI–LHCI. The PSI–ACPI supercomplex is composed of a monomeric PSI core containing 14 subunits, 12 of which originated in red algae, 1 diatom PsaR homolog, and an additional peptide. The PSI core is surrounded by 14 ACPI subunits that form 2 antenna layers: an inner layer with 11 ACPIs surrounding the PSI core and an outer layer containing 3 ACPIs. A pigment-binding subunit that is not present in any other previously characterized PSI–LHCI complexes, ACPI-S, mediates the association and energy transfer between the outer and inner ACPIs. The extensive pigment network of PSI–ACPI ensures efficient light harvesting, energy transfer, and dissipation. Overall, the PSI–LHCI structure identified in this study provides a framework for delineating the mechanisms of energy transfer in cryptophyte PSI–LHCI and for understanding the evolution of photosynthesis in the red lineage, which occurred via secondary endosymbiosis.

The cell of a rod-shaped bacterium is composed of a cylinder and two hemispherical poles. In recent decades, the molecular mechanism of morphogenesis in rod-shaped bacteria has received extensive research. However, most works have focused on the morphogenesis of cylinders, and the morphogenesis of the hemispherical poles remains unclear. In the past, the pole of bacterial cell wall was considered as a rigid hemispherical structure. However, our work indicated that the pole in the isolated sacculi from Bacillus subtilis was a flat structure instead of a hemisphere form. Further works showed that internal pressure was responsible for shaping the hemispherical poles, indicating an elastic nature of the cell wall in poles. In addition, we found that the internal pressure was able to transform septa into hemispherical shape which is similar to normal poles. Based on our work, we proposed a model for the internal pressure-induced formation of hemispherical poles in B. subtilis, and this work may provide new clues into basic knowledge of the morphogenesis of rod-shaped bacteria.

A novel Gram-negative, rod-shaped, aerobic, oxidase-positive and catalase-negative bacterium, designated strain SM1970T, was isolated from a seawater sample collected from the Mariana Trench. Strain SM1970T grew at 15-37 oC and with 1–5% (w/v) NaCl. It hydrolyzed colloidal chitin, agar and casein but did not reduce nitrate to nitrite. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SM1970T formed a distinct lineage close to the genus Catenovulum within the family Alteromonadaceae, sharing the highest sequence similarity (93.6%) with type strain of Catenovulum maritimum but < 93.0% sequence similarity with those of other known species in the class Gammaproteobacteria. The major fatty acids of strain SM1970T were summed feature 3 (C16: 1 ω7c and/or C16: 1 ω6c), C16: 0 and summed feature 8 (C18: 1 ω7c and/or C18: 1 ω6c). The major polar lipids of the strain included phosphatidylethanolamine and phosphatidylglycerol and its main respiratory quinone was ubiquinone 8. The draft genome of strain SM1970T consisted of 77 scaffolds and was 4,172,146 bp in length, containing a complete set of genes for chitin degradation. The average amino acid identity (AAI) values between SM1970T and type strains of known Catenovulum species were 56.6–57.1% while the percentage of conserved proteins (POCP) values between them were 28.5–31.5%. The genomic DNA G + C content of strain SM1970T was 40.1 mol%. On the basis of the polyphasic analysis, strain SM1970T is considered to represent a novel species in a novel genus of the family Alteromonadaceae, for which the name Marinifaba aquimaris is proposed with the type strain being SM1970T (= MCCC 1K04323T = KCTC 72844T).

A Gram-stain-negative, aerobic, ovoid-rod-shaped bacterium, designated strain SM1903T, was isolated from surface seawater of the Mariana Trench. The strain grew at 15–37 °C (optimum, 35 °C) and with 1–15 % (optimum, 4 %) NaCl. It hydrolysed aesculin but did not reduce nitrate to nitrite and hydrolyse Tween 80. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SM1903T formed a separate lineage within the family Rhodobacteraceae , sharing the highest 16S rRNA gene sequence similarity with type strains of Pseudooceanicola antarcticus (95.7 %) and Roseisalinus antarcticus (95.7 %). In phylogenetic trees based on single-copy OCs and whole proteins sequences, strain SM1903T fell within a sub-cluster encompassed by Oceanicola granulosus , Roseisalinus antarcticus and Histidinibacterium lentulum and formed a branch adjacent to Oceanicola granulosus . The major cellular fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c), C16 : 0 and 11-methyl-C18 : 1 ω7c. The polar lipids mainly comprised phosphatidylglycerol, phosphatidylcholine, one unidentified lipid, one unidentified aminolipid, and one unidentified glycolipid. The solo respiratory quinone was ubiquinone-10. The genomic DNA G+C content of strain SM1903T was 66.0 mol%. Based on the results of phenotypic, chemotaxonomic, and phylogenetic characterization for strain SM1903T, it is considered to represent a novel species of a novel genus in the family Rhodobacteraceae , for which the name Pelagovum pacificum gen. nov., sp. nov. is proposed. The type strain is SM1903T (=MCCC 1K03608T=KCTC 72046T).

A Gram-stain-negative, aerobic, polarly flagellated, straight or curved rod-shaped bacterium, designated strain M1K-6T, was isolated from deep seawater samples collected from the Mariana Trench. The strain grew at −4 to 37 °C (optimum, 25–30 °C), at pH 5.5–10.0 (optimum, pH 7.0) and with 0.5–14.0 % (w/v) NaCl (optimum, 2.0 %). It did not reduce nitrate to nitrite nor hydrolyse gelatin or starch. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain M1K-6T was affiliated with the genus Marinomonas , sharing 93.1–97.0 % sequence similarity with the type strains of recognized Marinomonas species. The major cellular fatty acids were summed feature 3 (C16 : 1 ω6c/C16 : 1 ω7c), summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C16 : 0, C10 : 0 3-OH and C18 : 0. The predominant respiratory quinone was ubiquinone-8. Polar lipids of strain M1K-6T included phosphatidylethanolamine, phosphatidylglycerol and two unidentified lipids. The genomic G+C content of strain M1K-6T was 46.0 mol%. Based on data from the present polyphasic study, strain M1K-6T was considered to represent a novel species within the genus Marinomonas , for which the name Marinomonas profundi sp. nov. is proposed. The type strain is M1K-6T (=KCTC 72501T=MCCC 1K03890T).

A Gram-stain-negative, aerobic, non-flagellated and rod- or ovoid-shaped bacterium, designated as strain S4J41T, was isolated from Antarctic intertidal sediment. The isolate grew at 0–37 °C and with 0.5–10 % (w/v) NaCl. It reduced nitrate to nitrite and hydrolysed Tween 80 and gelatin. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain S4J41T constituted a distinct phylogenetic line within the family Rhodobacteraceae and was closely related with some species in the genera Ruegeria , Phaeobacter , Pseudopuniceibacterium , Sulfitobacter , Puniceibacterium and Poseidonocella with 98.6–95.7 % 16S rRNA gene sequence similarities. The major cellular fatty acids were C16 : 0, summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C18 : 0 and the major polar lipids were phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, phosphatidylethanolamine and one unidentified aminolipid. The sole respiratory quinone was Q-10. The genomic DNA G+C content of strain S4J41T was 60.3 mol%. Based on the phylogenetic, chemotaxonomic and phenotypic data obtained in this study, strain S4J41T is considered to represent a novel species in a new genus within the family Rhodobacteraceae , for which the name Antarcticimicrobium sediminis gen. nov., sp. nov. is proposed. The type strain is S4J41T (=MCCC 1K03508T=KCTC 62793T). Moreover, the transfer of Ruegeria lutea Kim et al. 2019 to Antarcticimicrobium gen. nov. as Antarcticimicrobium luteum comb. nov. (type strain 318-1T=JCM 30927T=KCTC 72105T) is also proposed.

3,6-anhydro-α-L-galactose (L-AHG) is one of the main monosaccharide constituents of red macroalgae. In the recently discovered bacterial L-AHG catabolic pathway, L-AHG is first oxidized by a NAD(P)+-dependent dehydrogenase (AHGD), which is a key step of this pathway. However, the catalytic mechanism(s) of AHGDs is still unclear. Here, we identified and characterized an AHGD from marine bacterium Vibrio variabilis JCM 19239 (VvAHGD). The NADP+-dependent VvAHGD could efficiently oxidize L-AHG. Phylogenetic analysis suggested that VvAHGD and its homologs represent a new aldehyde dehydrogenase (ALDH) family with different substrate preferences from reported ALDH families, named the L-AHGDH family. To explain the catalytic mechanism of VvAHGD, we solved the structures of VvAHGD in the apo form and complex with NADP+ and modeled its structure with L-AHG. Based on structural, mutational, and biochemical analyses, the cofactor channel and the substrate channel of VvAHGD are identified, and the key residues involved in the binding of NADP+ and L-AHG and the catalysis are revealed. VvAHGD performs catalysis by controlling the consecutive connection and interruption of the cofactor channel and the substrate channel via the conformational changes of its two catalytic residues Cys282 and Glu248. Comparative analyses of structures and enzyme kinetics revealed that differences in the substrate channels (in shape, size, electrostatic surface, and residue composition) lead to the different substrate preferences of VvAHGD from other ALDHs. This study on VvAHGD sheds light on the diversified catalytic mechanisms and evolution of NAD(P)+-dependent ALDHs.\ud \ud

A Gram-stain-negative, facultatively anaerobic, flagellated and rod-shaped bacterium, designated strain SM1901T, was isolated from a brown algal sample collected from Kings Bay, Svalbard, Arctic. Strain SM1901T grew at −4‒30 °C and with 0–7.0 % (w/v) NaCl. It reduced nitrate to nitrite and hydrolysed DNA and Tween 80. Results of phylogenetic analyses based on 16S rRNA gene sequences indicated that strain SM1901T was affiliated with the genus Shewanella , showing the highest sequence similarity to the type strain of Shewanella litoralis (97.5%), followed by those of Shewanella vesiculosa , Shewanella livingstonensis and Shewanella saliphila (97.3 % for all three). The major cellular fatty acids were summed feature 3 (C16 : 1 ω7с and/or C16 : 1 ω6с), C16 : 0, C18 : 0, iso-C15 : 0 and C17 : 1 ω8с and the major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. The respiratory quinones were ubiquinones Q-7, Q-8, menaquinones MK-7(H) and MK-8. The genome of strain SM1901T was 4648537 nucleotides long and encoded a variety of cold adaptation related genes, providing clues for better understanding the ecological adaptation mechanisms of polar bacteria. The genomic DNA G+C content of strain SM1901T was 40.5 mol%. Based on the polyphasic evidence presented in this paper, strain SM1901T was considered to represent a novel species, constituting a novel psychrotolerant lineage out of the known SF clade encompassed by polar Shewanella species, within the genus Shewanella , for which the name Shewanella polaris sp. nov. is proposed. The type strain is SM1901T (=KCTC 72047T=MCCC 1K03585T).

Vibrio collagenases of the M9A subfamily are closely related to Vibrio pathogenesis for their role in collagen degradation during host invasion. Although some Vibrio collagenases have been characterized, the collagen degradation mechanism of Vibrio collagenase is still largely unknown. Here, an M9A collagenase, VP397, from marine Vibrio pomeroyi strain 12613 was characterized, and its fragmentation pattern on insoluble type I collagen fibers was studied. VP397 is a typical Vibrio collagenase composed of a catalytic module featuring a peptidase M9N domain and a peptidase M9 domain and two accessory bacterial prepeptidase C-terminal domains (PPC domains). It can hydrolyze various collagenous substrates, including fish collagen, mammalian collagens of types I to V, triple-helical peptide [(POG)(10)](3), gelatin, and 4-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-o-Arg (Pz-peptide). Atomic force microscopy (AFM) observation and biochemical analyses revealed that VP397 first assaults the C-telopeptide region to dismantle the compact structure of collagen and dissociate tropocollagen fragments, which are further digested into peptides and amino acids by VP397 mainly at the Y-Gly bonds in the repeating Gly-X-Y triplets. In addition, domain deletion mutagenesis showed that the catalytic module of VP397 alone is capable of hydrolyzing type I collagen fibers and that its C-terminal PPC2 domain functions as a collagen-binding domain during collagenolysis. Based on our results, a model for the collagenolytic mechanism of VP397 is proposed. This study sheds light on the mechanism of collagen degradation by Vibrio collagenase, offering a better understanding of the pathogenesis of Vibrio and helping in developing the potential applications of Vibrio collagenase in industrial and medical areas. IMPORTANCE Many Vibrio species are pathogens and cause serious diseases in humans and aquatic animals. The collagenases produced by pathogenic Vibrio species have been regarded as important virulence factors, which occasionally exhibit direct pathogenicity to the infected host or facilitate other toxins’ diffusion through the digestion of host collagen. However, our knowledge concerning the collagen degradation mechanism of Vibrio collagenase is still limited. This study reveals the degradation strategy of Vibrio collagenase VP397 on type I collagen. VP397 binds on collagen fibrils via its C-terminal PPC2 domain, and its catalytic module first assaults the C-telopeptide region and then attacks the Y-Gly bonds in the dissociated tropocollagen fragments to release peptides and amino acids. This study offers new knowledge regarding the collagenolytic mechanism of Vibrio collagenase, which is helpful for better understanding the role of collagenase in Vibrio pathogenesis and for developing its industrial and medical applications.

Bacterial polar flagella, comprised of flagellin, are essential for bacterial motility. Pseudoalteromonas sp. strain SM9913 is a bacterium isolated from deep-sea sediments. Unlike other Pseudoalteromonas strains that have a long polar flagellum, strain SM9913 has an abnormally short polar flagellum. Here, we investigated the underlying reason for the short flagellum and found that a single-base mutation was responsible for the altered flagellar assembly. This mutation leads to the fragmentation of the flagellin gene into two genes, PSM_A2281, encoding the core segment and the C-terminal segment, and PSM_A2282, encoding the N-terminal segment, and only gene PSM_A2281 is involved in the production of the short polar flagellum. When a chimeric gene of PSM_A2281 and PSM_A2282 encoding an intact flagellin, A2281::82, was expressed, a long polar flagellum was produced, indicating that the N-terminal segment of flagellin contributes to the production of a polar flagellum of a normal length. Analyses of the simulated structures of A2281 and A2281::82 and that of the flagellar filament assembled with A2281::82 indicate that due to the lack of two α-helices, the core of the flagellar filament assembled with A2281 is incomplete and is likely too weak to support the stability and movement of a long flagellum. This mutation in strain SM9913 had little effect on its growth and only a small effect on its swimming motility, implying that strain SM9913 can live well with this mutation in natural sedimentary environments. This study provides a better understanding of the assembly and production of bacterial flagella. IMPORTANCE Polar flagella, which are essential organelles for bacterial motility, are comprised of multiple flagellin subunits. A flagellin molecule contains an N-terminal segment, a core segment, and a C-terminal segment. The results of this investigation of the deep-sea sedimentary bacterium Pseudoalteromonas sp. strain SM9913 demonstrate that a single-base mutation in the flagellin gene leads to the production of an incomplete flagellin without the N-terminal segment and that the loss of the N-terminal segment of the flagellin protein results in the production of a shortened polar flagellar filament. Our results shed light on the important function of the N-terminal segment of flagellin in the assembly and stability of bacterial flagellar filament.

Bacterial polar flagella, comprised of flagellin, are essential for bacterial motility. Pseudoalteromonas sp. strain SM9913 is a bacterium isolated from deep-sea sediments. Unlike other Pseudoalteromonas strains that have a long polar flagellum, strain SM9913 has an abnormally short polar flagellum. Here, we investigated the underlying reason for the short flagellum and found that a single-base mutation was responsible for the altered flagellar assembly. This mutation leads to the fragmentation of the flagellin gene into two genes, PSM_A2281, encoding the core segment and the C-terminal segment, and PSM_A2282, encoding the N-terminal segment, and only gene PSM_A2281 is involved in the production of the short polar flagellum. When a chimeric gene of PSM_A2281 and PSM_A2282 encoding an intact flagellin, A2281::82, was expressed, a long polar flagellum was produced, indicating that the N-terminal segment of flagellin contributes to the production of a polar flagellum of a normal length. Analyses of the simulated structures of A2281 and A2281::82 and that of the flagellar filament assembled with A2281::82 indicate that due to the lack of two α-helices, the core of the flagellar filament assembled with A2281 is incomplete and is likely too weak to support the stability and movement of a long flagellum. This mutation in strain SM9913 had little effect on its growth and only a small effect on its swimming motility, implying that strain SM9913 can live well with this mutation in natural sedimentary environments. This study provides a better understanding of the assembly and production of bacterial flagella. IMPORTANCE Polar flagella, which are essential organelles for bacterial motility, are comprised of multiple flagellin subunits. A flagellin molecule contains an N-terminal segment, a core segment, and a C-terminal segment. The results of this investigation of the deep-sea sedimentary bacterium Pseudoalteromonas sp. strain SM9913 demonstrate that a single-base mutation in the flagellin gene leads to the production of an incomplete flagellin without the N-terminal segment and that the loss of the N-terminal segment of the flagellin protein results in the production of a shortened polar flagellar filament. Our results shed light on the important function of the N-terminal segment of flagellin in the assembly and stability of bacterial flagellar filament.

Predator-prey interactions play important roles in the cycling of marine organic matter. Here we show that a Gram-negative bacterium isolated from marine sediments (Pseudoalteromonas sp. strain CF6-2) can kill Gram-positive bacteria of diverse peptidoglycan (PG) chemotypes by secreting the metalloprotease pseudoalterin. Secretion of the enzyme requires a Type II secretion system. Pseudoalterin binds to the glycan strands of Gram positive bacterial PG and degrades the PG peptide chains, leading to cell death. The released nutrients, including PG-derived D-amino acids, can then be utilized by strain CF6-2 for growth. Pseudoalterin synthesis is induced by PG degradation products such as glycine and glycine-rich oligopeptides. Genes encoding putative pseudoalterin-like proteins are found in many other marine bacteria. This study reveals a new microbial interaction in the ocean., Predator-prey interactions play important roles in the cycling of marine organic matter. Here the authors show that a Gram-negative bacterium isolated from marine sediments can kill and feed on Gram-positive bacteria by secreting a peptidoglycan-degrading enzyme.

A Gram-stain-negative, aerobic, flagellated, rod-shaped bacterial strain, SM1705T, was isolated from a surface seawater sample collected from the South China Sea. The strain grew at 10–40 °C and with 0.5–13.0 % (w/v) NaCl. It hydrolysed Tweens 20, 40 and 60, but did not hydrolyse starch or Tween 80 nor reduce nitrate to nitrite. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SM1705T was affiliated with the genus Parvularcula , sharing the highest sequence similarity (96.0 %) with type strain of Parvularcula bermudensis and forming a coherent branch together with the latter within the clade of Parvularcula . The major cellular fatty acids were identified as summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c), C16 : 0 and C18 : 0. Polar lipids included three unidentified glycolipids and one unidentified lipid. The major respiratory quinone of strain SM1705T was Q10. The genomic DNA G+C content of strain SM1705T was 59.3 mol%. Based on the polyphasic evidence presented in this paper, strain SM1705T represents a novel Parvularcula species, for which the name Parvularcula marina sp. nov. is proposed. The type strain is SM1705T (=KCTC 62795T=MCCC 1K03505T=CCTCC AB 2018345T).

Accumulation of trimethylamine N-oxide improves both growth and survival of deep-sea bacteria under high hydrostatic pressure., High hydrostatic pressure (HHP) is a characteristic environmental factor of the deep ocean. However, it remains unclear how piezotolerant bacteria adapt to HHP. Here, we identify a two-step metabolic pathway to cope with HHP stress in a piezotolerant bacterium. Myroides profundi D25T, obtained from a deep-sea sediment, can take up trimethylamine (TMA) through a previously unidentified TMA transporter, TmaT, and oxidize intracellular TMA into trimethylamine N-oxide (TMAO) by a TMA monooxygenase, MpTmm. The produced TMAO is accumulated in the cell, functioning as a piezolyte, improving both growth and survival at HHP. The function of the TmaT-MpTmm pathway was further confirmed by introducing it into Escherichia coli and Bacillus subtilis. Encoded TmaT-like and MpTmm-like sequences extensively exist in marine metagenomes, and other marine Bacteroidetes bacteria containing genes encoding TmaT-like and MpTmm-like proteins also have improved HHP tolerance in the presence of TMA, implying the universality of this HHP tolerance strategy in marine Bacteroidetes.

A novel Gram-negative, rod-shaped, aerobic, oxidase-positive and catalase-negative bacterium, designated strain SM1970

Cell division of Staphylococcus adopts a “popping” mechanism that mediates extremely rapid separation of the septum. Elucidating the structure of the septum is crucial for understanding this exceptional bacterial cell division mechanism. Here, the septum structure of Staphylococcus warneri was extensively characterized using high-speed time-lapse confocal microscopy, atomic force microscopy, and electron microscopy. The cells of S. warneri divide in a fast popping manner on a millisecond timescale. Our results show that the septum is composed of two separable layers, providing a structural basis for the ultrafast daughter cell separation. The septum is formed progressively toward the center with nonuniform thickness of the septal disk in radial directions. The peptidoglycan on the inner surface of double-layered septa is organized into concentric rings, which are generated along with septum formation. Moreover, this study signifies the importance of new septum formation in initiating new cell cycles. This work unravels the structural basis underlying the popping mechanism that drives S. warneri cell division and reveals a generic structure of the bacterial cell. IMPORTANCE This work shows that the septum of Staphylococcus warneri is composed of two layers and that the peptidoglycan on the inner surface of the double-layered septum is organized into concentric rings. Moreover, new cell cycles of S. warneri can be initiated before the previous cell cycle is complete. This work advances our knowledge about a basic structure of bacterial cell and provides information on the double-layered structure of the septum for bacteria that divide with the “popping” mechanism.

The cell of a rod-shaped bacterium is composed of a cylinder and two hemispherical poles. In recent decades, the molecular mechanism of morphogenesis in rod-shaped bacteria has received extensive research. However, most works have focused on the morphogenesis of cylinders, and the morphogenesis of the hemispherical poles remains unclear. In the past, the pole of bacterial cell wall was considered as a rigid hemispherical structure. However, our work indicated that the pole in the isolated sacculi from Bacillus subtilis was a flat structure instead of a hemisphere form. Further works showed that internal pressure was responsible for shaping the hemispherical poles, indicating an elastic nature of the cell wall in poles. In addition, we found that the internal pressure was able to transform septa into hemispherical shape which is similar to normal poles. Based on our work, we proposed a model for the internal pressure-induced formation of hemispherical poles in B. subtilis, and this work may provide new clues into basic knowledge of the morphogenesis of rod-shaped bacteria.

Cell division of Staphylococcus adopts a “popping” mechanism that mediates extremely rapid separation of the septum. Elucidating the structure of the septum is crucial for understanding this exceptional bacterial cell division mechanism. Here, the septum structure of Staphylococcus warneri is extensively characterized using high-speed time-lapse confocal microscopy, atomic force microscopy, and electron microscopy. The cells of S. warneri divide in a fast “popping” manner on a millisecond timescale. Our results show that the septum is composed of two separable layers, providing a structural basis for the ultrafast daughter cell separation. The septum is formed progressively toward the center with non-uniform thickness of the septal disk in radial directions. The peptidoglycan on the inner surface of double-layered septa is organized into concentric rings, which are generated along with septum formation. Moreover, this study signifies the importance of new septum formation in initiating new cell cycles. This work unravels the structural basis underlying the “popping” mechanism that drives Staphylococcus cell division and reveals a generic structure of the bacterial cell.IMPORTRANCEThis work shows that the septum of Staphylococcus warneri is composed of two layers and the peptidoglycan on the inner surface of the double-layered septum is organized into concentric rings. Moreover, new cell cycles of Staphylococcus could be initiated before the previous cell cycle is complete. This work advances our knowledge about a basic structure of bacterial cell and provides the double layered structural information of septum for the bacterium that divide with the “popping” mechanism.

Polysaccharides are secreted by many marine bacteria as a strategy for growth, binding trace metals, adhering to solid surfaces, and to survive adverse conditions. Therefore, they have attracted extensive research interest due to their biological roles as well as potential industrial application. Many works have been carried out to study the growth dynamics of polysaccharides producing bacteria. Average polysaccharide production per cell during growth were usually studied in the past. However, most previous works were carried out at the population level, and the research at a single cell level was rare. Atomic force microscopy (AFM) is a powerful tool in studying single microorganisms and their extracellular polysaccharides. Here we investigated the growth dynamics and capsular polysaccharide (CPS) production of a CPS producing bacterium Zunongwangia profunda SM-A87 isolated from deep-sea sediments with AFM. Z. profunda SM-A87 exhibited slow growth rates at 10 °C, which was lower than at optimum growth temperature (30 °C). But the CPS production at 10 °C was much higher than that at 30 °C. Single cell imaging with AFM revealed rod like cell morphology at both temperatures, but filamentous bacteria could sometimes be noticed at 10 °C. The CPSs surrounding bacterial cells were observed, and the fibrils of polysaccharides entangled into networks. The diameter of the capsules and the length of the polysaccharides fibrils increased as cultivation time increased. The average volume of the bacterial cells and capsular polysaccharides surrounding each cell at both temperatures were calculated. The average volume of a single bacterial cell was 0.2–0.3 µm 3 , and it increased in exponential phase and slightly decreased in stationary phase, but the average volume of CPS produced by single cells increased during bacterial growth. CPS production increased to 0.097 ± 0.051 µm 3 per cell at 10 °C in stationary phase, which is larger than that produced at 30 °C (0.055 ± 0.013 µm 3 per cell). We report a novel method of estimating the average bacterial polysaccharide production with AFM. Since polysaccharides-producing bacteria are abundant in marine sediments, this method is potentially useful for studying the biological and ecological role of polysaccharides-producing bacteria from the deep sea in the future.

Nitrogen is one of the most important nutrients needed for plants and algae to survive, and the photosynthetic ability of algae is related to nitrogen abundance. Red algae are unique photosynthetic eukaryotic organisms in the evolution of algae, as they contain phycobilisomes (PBSs) on their thylakoid membranes. In this report, the in vivo chlorophyll (Chl) a fluorescence kinetics of nitrogen-starved Porphyridium cruentum were analyzed to determine the effects of nitrogen deficiency on photosynthetic performance using a multi-color pulse amplitude modulation (PAM) chlorophyll fluorometer. Due to nitrogen starvation, the photochemical efficiency of PSII and the activity of PSII reaction centers (RCs) decreased, and photoinhibition of PSII occurred. The water-splitting system on the donor side of PSII was seriously impacted by nitrogen deficiency, leading to the inactivation of the oxygen-evolving complex (OEC) and decreased light energy conversion efficiency. In nitrogen-starved cells, a higher proportion of energy was used for photochemical reactions, and thermal dissipation was reduced, as shown by qP and qN. The ability of nitrogen-starved cells to tolerate and resist high photon flux densities was weakened. Our results showed that the photosynthetic performance of P. cruentum was severely impacted by nitrogen deficiency.

The cold adaptation mechanism of phycobiliproteins, the major photosynthetic pigment-proteins in cyanobacteria and red algae, has rarely been studied. Here we reported the biochemical, structural, and molecular dynamics simulation study of the C-phycocyanin from Arctic cyanobacterial strain Pseudanabaena sp. LW0831. We characterized the phycobilisome components of LW0831 and obtained their gene sequences. Compared to the mesophilic counterpart from Arthrospira platensis (Ar-C-PC), LW0831 C-phycocyanin (Ps-C-PC) has a decreased thermostability (∆ Tm of − 16 °C), one of the typical features of cold-adapted enzymes. To uncover its structural basis, we resolved the crystal structure of Ps-C-PC 1 at 2.04 A. Consistent with the decrease in thermostability, comparative structural analyses revealed decreased intra-trimer and inter-trimer interactions in Ps-C-PC 1, compared to Ar-C-PC. However, comparative molecular dynamics simulations indicated that Ps-C-PC 1 shows similar flexibilities to Ar-C-PC for both the (αβ)3 trimer and (αβ)6 hexamer. Therefore, the optimization mode is clearly different from cold-adapted enzymes, which usually have increased flexibilities. Detailed analyses demonstrated different optimization modes for the α and β subunits and it was revealed that hydrophobic interactions are key to this difference, though salt bridges, hydrogen bonds, and surface hydrophobicity are also involved. This study is the first report of the structure of cold-adapted phycobiliproteins and provides insights into the cold-adaptation strategies of non-enzyme proteins.

Trimethylamine (TMA) and trimethylamine N-oxide (TMAO) are widespread in the ocean and are important nitrogen source for bacteria. TMA monooxygenase (Tmm), a bacterial flavin-containing monooxygenase (FMO), is found widespread in marine bacteria and is responsible for converting TMA to TMAO. However, the molecular mechanism of TMA oxygenation by Tmm has not been explained. Here, we determined the crystal structures of two reaction intermediates of a marine bacterial Tmm (RnTmm) and elucidated the catalytic mechanism of TMA oxidation by RnTmm. The catalytic process of Tmm consists of a reductive half-reaction and an oxidative half-reaction. In the reductive half-reaction, FAD is reduced and a C4a-hydroperoxyflavin intermediate forms. In the oxidative half-reaction, this intermediate attracts TMA through electronic interactions. After TMA binding, NADP+ bends and interacts with D317, shutting off the entrance to create a protected micro-environment for catalysis and exposing C4a-hydroperoxyflavin to TMA for oxidation. Sequence analysis suggests that the proposed catalytic mechanism is common for bacterial Tmms. These findings reveal the catalytic process of TMA oxidation by marine bacterial Tmm and first show that NADP+ undergoes a conformational change in the oxidative half-reaction of FMOs.

The availability of nitrogen is one of the most important determinants that can limit the growth of photosynthetic organisms including plants and algae; however, direct observations on the supramolecular architecture of photosynthetic membranes in response to nitrogen stress are still lacking. Red algae are an important evolutionary group of algae which contain phycobilisomes (PBSs) on their thylakoid membranes, as do cyanobacteria. PBSs function not only as light-harvesting antennae but also as nitrogen storage. In this report, alterations of the supramolecular architecture of thylakoid membranes from red alga Porphyridium cruentum during nitrogen starvation were characterized. The morphology of the intact thylakoid membrane was observed to be round vesicles. Thylakoid membranes were reduced in content and PBSs were degraded during nitrogen starvation. The size and density of PBSs were both found to be reduced. PBS size decreased by less than one-half after 20days of nitrogen starvation, but their hemispherical morphology was retained. The density of PBSs on thylakoid membranes was more seriously affected as time proceeded. Upon re-addition of nitrogen led to increasing of PBSs on thylakoid membranes. This work reports the first direct observation on alterations in the supramolecular architecture of thylakoid membranes from a photosynthetic organism in response to nitrogen stress.

Microorganisms display diverse biogeographic patterns in the three-dimensional contiguous seawater. The distance-decay relationship, the change in species composition similarity between different communities over a geographic distance, is a commonly observed biogeographic pattern. To study biogeographic patterns and the corresponding driving forces, the bacterial distance-decay patterns along the horizontal and vertical dimensions in the South China Sea (SCS) were investigated through the sequencing of partial 16 S rRNA gene regions. Along the horizontal geographical distances (up to ~1000 km), no significant distance-decay pattern in community compositions was observed in any of the tested seawater layers. However, vertical depths (up to ~4 km) had strong effects on bacterial community variation, which was apparently governed by dispersal barriers due to limited water mass mixing. In addition, community variations in the vertical direction were strongly correlated with the prominent variation of environmental factors. Apparently, the changes in bacterial community compositions along vertical distances were much greater than those along horizontal distances. The results showed that the distance-decay relationship in bacterial communities at the medium spatial scale was associated with vertical depth rather than with horizontal distance, even though the horizontal distance is much larger than the vertical distance in the open SCS.

A yellow-pigmented, rod-shaped, non-flagellated, aerobic and Gram-reaction-negative bacterium, designated strain SM1212T, was isolated from intertidal sand of Kongsfjorden, Svalbard. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain SM1212T constituted a distinct lineage within the family Flavobacteriaceae. It shared highest 16S rRNA gene sequence similarities with the type strains of Bizionia echini (96.0 %), Lacinutrix jangbogonensis (95.8 %) and Psychroserpens damuponensis (95.7 %) and

Trimethylamine N -oxide (TMAO) is an important nitrogen source for marine bacteria. TMAO can also be metabolized by marine bacteria into volatile methylated amines, the precursors of the greenhouse gas nitrous oxide. However, it was not known how TMAO is recognized and imported by bacteria. Ruegeria pomeroyi DSS-3, a marine Roseobacter , has an ATP-binding cassette transporter, TmoXWV, specific for TMAO. TmoX is the substrate-binding protein of the TmoXWV transporter. In this study, the substrate specificity of TmoX of R. pomeroyi DSS-3 was characterized. We further determined the structure of the TmoX/TMAO complex and studied the TMAO-binding mechanism of TmoX by biochemical, structural, and mutational analyses. A Ca 2+ ion chelated by an extended loop in TmoX was shown to be important for maintaining the stability of TmoX. Molecular dynamics simulations indicate that TmoX can alternate between “open” and “closed” states for binding TMAO. In the substrate-binding pocket, four tryptophan residues interact with the quaternary amine of TMAO by cation-π interactions, and Glu131 forms a hydrogen bond with the polar oxygen atom of TMAO. The π-π stacking interactions between the side chains of Phe and Trp are also essential for TMAO binding. Sequence analysis suggests that the TMAO-binding mechanism of TmoX may have universal significance in marine bacteria, especially in the marine Roseobacter clade. This study sheds light on how marine microorganisms utilize TMAO. IMPORTANCE Trimethylamine N -oxide (TMAO) is an important nitrogen source for marine bacteria. The products of TMAO metabolized by bacteria are part of the precursors of the greenhouse gas nitrous oxide. It is unclear how TMAO is recognized and imported by bacteria. TmoX is the substrate-binding protein of a TMAO-specific transporter. Here, the substrate specificity of TmoX of Ruegeria pomeroyi DSS-3 was characterized. The TMAO-binding mechanism of TmoX was studied by biochemical, structural, and mutational analyses. Moreover, our results suggest that the TMAO-binding mechanism may have universal significance in marine bacteria. This study sheds light on how marine microorganisms utilize TMAO and should lead to a better understanding of marine nitrogen cycling.

A novel Gram-stain-negative, oxidase- and catalase-positive, aerobic bacterium, designated strain SM1351T, was isolated from surface seawater of the Atlantic Ocean. This strain grew at 4-45 °C and with 5-90 g NaCl l- 1. It did not reduce nitrate to nitrite and could not hydrolyse starch or DNA. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the strain was affiliated with the genus Haliea in the family Alteromonadaceae, with sequence similarities with the type strains of Haliea salexigens and Haliea mediterranea, the two recognized species of the genus Haliea, of 96.2 and 94.6 %, respectively. The major fatty acids of strain SM1351T were C16 : 1ω7c and/or iso-C15 : 0 2-OH, C17 : 1ω8c, C18 : 1ω7c and C16 : 0 and the major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The major respiratory quinone was ubiquinone Q-8. The genomic DNA G+C content of strain SM1351T was 62 mol%. On the basis of the polyphasic characterization of strain SM1351T in this study, it is considered to represent a novel species in the genus Haliea, for which the name Haliea atlantica sp. nov. is proposed. The type strain is SM1351T ( = CCTCC AB 2014266T = JCM 30304T). Moreover, the transfer of Haliea mediterraneaLucena et al. 2010 to Parahaliea gen. nov. as Parahaliea mediterranea comb. nov. (type strain 7SM29T = CECT 7447T = DSM 21924T) and an emended description of the genus Haliea are also proposed.

The microbial cleavage of dimethylsulfoniopropionate (DMSP) generates volatile dimethyl sulfide (DMS) and is an important step in global sulfur and carbon cycles. DddP is a DMSP lyase in marine bacteria, and the deduced dddP gene product is abundant in marine metagenomic data sets. However, DddP belongs to the M24 peptidase family according to sequence alignment. Peptidases hydrolyze C-N bonds, but DddP is deduced to cleave C-S bonds. Mechanisms responsible for this striking functional shift are currently unknown. We determined the structures of DMSP lyase RlDddP (the DddP from Ruegeria lacuscaerulensis ITI_1157) bound to inhibitory 2-(N-morpholino) ethanesulfonic acid or PO4 (3-) and of two mutants of RlDddP bound to acrylate. Based on structural, mutational and biochemical analyses, we characterized a new ion-shift catalytic mechanism of RlDddP for DMSP cleavage. Furthermore, we suggested the structural mechanism leading to the loss of peptidase activity and the subsequent development of DMSP lyase activity in DddP. This study sheds light on the catalytic mechanism and the divergent evolution of DddP, leading to a better understanding of marine bacterial DMSP catabolism and global DMS production.

A novel Gram-stain-negative, aerobic, orange-pigmented, non-flagellated, gliding, rod-shaped bacterium, designated strain SM1354T was isolated from surface seawater of the Atlantic Ocean. The strain hydrolysed gelatin and DNA but did not reduce nitrate. It grew at 4–40 °C and with 0.5–11 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene sequences revealed that strain SM1354T belonged to the genus Marivirga with 96.0–96.2 % sequence similarities to known species of the genus Marivirga . The major fatty acids of strain SM1354T were iso-C15 : 0, iso-C15 : 1 G, iso-C17 : 03-OH and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 02-OH). Polar lipids of strain SM1354T included phosphatidylethanolamine, three unidentified lipids and one unidentified aminolipid and aminophospholipid. The major respiratory quinone of strain SM1354T was menaquinone 7 (MK-7). The genomic DNA G+C content of strain SM1354T was 33.9±0.4 mol%. On the basis of the results of the polyphasic characterization in this study, it is proposed that strain SM1354T represents a novel species of the genus Marivirga , namely Marivirga atlantica sp. nov. The type strain of Marivirga atlantica is SM1354T ( = CCTCC AB 2014242T = JCM 30305T). An emended description of the genus Marivirga is also proposed.

Although bacteriobenthos play a major role in the degradation of particulate organic matter in marine sediment, knowledge of the sediment-adapted lifestyles of bacteriobenthos is still scarce. Here, the particle-associated, swimming and swarming lifestyles of the benthonic bacterium Pseudoalteromonas sp. SM9913 (SM9913) were illustrated. SM9913 had a clay particle-associated lifestyle, and its exopolysaccharide played an important role in this lifestyle. SM9913 also had swimming and swarming motilities, indicating that it may have swimming and swarming lifestyles in the sediment. The lateral flagella were responsible for the swarming motility, and the polar flagella were responsible for the swimming motility. Iron limitation was an indispensable inductive signal of the swarming motility. An analysis of the motilities of SM9913 and its mutants in clay demonstrated that SM9913 moved in clay by both swimming and swarming motilities. Genomic analysis suggests that having two flagella systems is most likely a common adaptation of some bacteriobenthos to the sediment environment. Our results reveal the lifestyles of benthonic SM9913, providing a better understanding of the environmental adaptation of benthonic bacteria.

Halotolerant enzymes are beneficial for industrial processes requiring high salt concentrations and low water activity. Most halophilic proteins are evolved to have reduced hydrophobic interactions on the surface and in the hydrophobic cores for their haloadaptation. However, in this study, we improved the halotolerance of a thermolabile esterase, E40, by increasing intraprotein hydrophobic interactions. E40 was quite unstable in buffers containing more than 0.3 M NaCl, and its k cat and substrate affinity were both significantly reduced in 0.5 M NaCl. By introducing hydrophobic residues in loop 1 of the CAP domain and/or α7 of the catalytic domain in E40, we obtained several mutants with improved halotolerance, and the M3 S202W I203F mutant was the most halotolerant. (“M3” represents a mutation in loop 1 of the CAP domain in which residues R22-K23-T24 of E40 are replaced by residues Y22-K23-H24-L25-S26 of Est2.) Then we solved the crystal structures of the S202W I203F and M3 S202W I203F mutants to reveal the structural basis for their improved halotolerance. Structural analysis revealed that the introduction of hydrophobic residues W202 and F203 in α7 significantly improved E40 halotolerance by strengthening intradomain hydrophobic interactions of F203 with W202 and other residues in the catalytic domain. By further introducing hydrophobic residues in loop 1, the M3 S202W I203F mutant became more rigid and halotolerant due to the formation of additional interdomain hydrophobic interactions between the introduced Y22 in loop 1 and W204 in α7. These results indicate that increasing intraprotein hydrophobic interactions is also a way to improve the halotolerance of enzymes with industrial potential under high-salt conditions. IMPORTANCE Esterases and lipases for industrial application are often subjected to harsh conditions such as high salt concentrations, low water activity, and the presence of organic solvents. However, reports on halotolerant esterases and lipases are limited, and the underlying mechanism for their halotolerance is still unclear due to the lack of structures. In this study, we focused on the improvement of the halotolerance of a salt-sensitive esterase, E40, and the underlying mechanism. The halotolerance of E40 was significantly improved by introducing hydrophobic residues. Comparative structural analysis of E40 and its halotolerant mutants revealed that increased intraprotein hydrophobic interactions make these mutants more rigid and more stable than the wild type against high concentrations of salts. This study shows a new way to improve enzyme halotolerance, which is helpful for protein engineering of salt-sensitive enzymes.

Sea ice is one of the most frigid environments for marine microbes. In contrast to other ocean ecosystems, microbes in permanent sea ice are space confined and subject to many extreme conditions, which change on a seasonal basis. How these microbial communities are regulated to survive the extreme sea ice environment is largely unknown. Here, we show that filamentous phages regulate the host bacterial community to improve survival of the host in permanent Arctic sea ice. We isolated a filamentous phage, f327, from an Arctic sea ice Pseudoalteromonas strain, and we demonstrated that this type of phage is widely distributed in Arctic sea ice. Growth experiments and transcriptome analysis indicated that this phage decreases the host growth rate, cell density and tolerance to NaCl and H2O2, but enhances its motility and chemotaxis. Our results suggest that the presence of the filamentous phage may be beneficial for survival of the host community in sea ice in winter, which is characterized by polar night, nutrient deficiency and high salinity, and that the filamentous phage may help avoid over blooming of the host in sea ice in summer, which is characterized by polar day, rich nutrient availability, intense radiation and high concentration of H2O2. Thus, while they cannot kill the host cells by lysing them, filamentous phages confer properties advantageous to host survival in the Arctic sea ice environment. Our study provides a foremost insight into the ecological role of filamentous phages in the Arctic sea ice ecosystem.

A Gram-stain-negative, aerobic, oxidase- and catalase-positive, flagellated, rod-shaped bacterial strain, designated SM1222T, was isolated from the deep-sea sediment of the South China Sea. The strain grew at 4–35 °C and with 0.5–8 % NaCl (w/v). Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain SM1222T was affiliated with the genus Oceanisphaera in the class Gammaproteobacteria . It shared the highest sequence similarity with the type strain of Oceanisphaera ostreae (96.8 %) and 95.4–96.6 % sequence similarities with type strains of other species of the genus Oceanisphaera with validly published names. Strain SM1222T contained summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH), C18 : 1ω7c, C16 : 0, C12 : 0 and summed feature 2 (C14 : 0 3-OH and/or iso-C16 : 1 I) as the major fatty acids and ubiquinone Q-8 as the predominant respiratory quinone. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The genomic DNA G+C content of strain SM1222T was 51.5 mol%. On the basis of the evidence presented in this study, strain SM1222T represents a novel species of the genus Oceanisphaera , for which the name Oceanisphaera profunda sp. nov. is proposed. The type strain of Oceanisphaera profunda is SM1222T ( = CCTCC AB 2013241T = KCTC 32510T). An emended description of the genus Oceanisphaera Romanenko et al. 2003 emend. Choi et al. 2011 is also proposed.

Traditional frequency power and test equipment cannot meet the requirements. This paper discusses in detail the composition of FM type series resonance test device, technical principles, characteristics and advantages. And also introduces wiring method, test methods, test standard. The instance proves that discharge test of large transformer using the FM series resonance device is convenient and accurate.

The microbial cleavage of dimethylsulfoniopropionate (DMSP) generates volatile DMS through the action of DMSP lyases and is important in the global sulfur and carbon cycles. When released into the atmosphere from the oceans, DMS is oxidized, forming cloud condensation nuclei that may influence weather and climate. Six different DMSP lyase genes are found in taxonomically diverse microorganisms, and dddQ is among the most abundant in marine metagenomes. Here, we examine the molecular mechanism of DMSP cleavage by the DMSP lyase, DddQ, from Ruegeria lacuscaerulensis ITI_1157. The structures of DddQ bound to an inhibitory molecule 2-(N-morpholino)ethanesulfonic acid and of DddQ inactivated by a Tyr131Ala mutation and bound to DMSP were solved. DddQ adopts a β-barrel fold structure and contains a Zn2+ ion and six highly conserved hydrophilic residues (Tyr120, His123, His125, Glu129, Tyr131, and His163) in the active site. Mutational and biochemical analyses indicate that these hydrophilic residues are essential to catalysis. In particular, Tyr131 undergoes a conformational change during catalysis, acting as a base to initiate the β-elimination reaction in DMSP lysis. Moreover, structural analyses and molecular dynamics simulations indicate that two loops over the substrate-binding pocket of DddQ can alternate between “open” and “closed” states, serving as a gate for DMSP entry. We also propose a molecular mechanism for DMS production through DMSP cleavage. Our study provides important insight into the mechanism involved in the conversion of DMSP into DMS, which should lead to a better understanding of this globally important biogeochemical reaction.

D-Spacing is the most significant topographic feature of type I collagen fibril, and it is important for our understanding of the structure and function in collagens. Traditionally, the D-spacing of type I collagen fibril was shown to have a singular value of 67 nm, but recent works indicated that the D-spacing values have a large distribution of up to 10 nm when measured by atomic force microscopy. We found that this large distribution of D-spacing values mainly resulted from image drift during measurement. Note that the D-spacing was homogeneous in a single type I collagen fibril. Our statistical analysis indicated that the D-spacing values of type I collagen fibrils exhibited only a narrow distribution of 2.5 nm around the value of 67 nm. In addition, the D-spacing values of the collagen fibrils were nearly identical not only within a single fibril bundle, but also in different fibril bundles. The measurement of the D-spacing values of collagen may provide important structural information in many research areas such as collagen related diseases, construction of molecular model of collagen, and collagen fibrogenesis.

A number of proteases in the subtilisin family derived from environmental or pathogenic microorganisms have been reported to be collagenolytic serine proteases. However, their collagen degradation mechanisms remain unclear. Here, the degradation mechanism of type I collagen fibres by the S8 collagenolytic protease MCP-01, from Pseudoalteromonas sp. SM9913, was studied. Atomic force microscopy observation and biochemical analysis confirmed that MCP-01 progressively released single fibrils from collagen fibres and released collagen monomers from fibrils mainly by hydrolysing proteoglycans and telopeptides in the collagen fibres. Structural and mutational analyses indicated that an enlarged substrate-binding pocket, mainly composed of loops 7, 9 and 11, is necessary for collagen recognition and that the acidic and aromatic residues on these loops form a negatively charged, hydrophobic environment for collagen binding. MCP-01 displayed a non-strict preference for peptide bonds with Pro or basic residues at the P1 site and/or Gly at the P1' site in collagen. His211 is a key residue for the P1-basic-residue preference of MCP-01. Our study gives structural and mechanistic insights into collagen degradation of the S8 collagenolytic protease, which is helpful in developing therapeutics for diseases with S8 collagenolytic proteases as pathogenic factors and in studying environmental organic nitrogen degradation mechanisms.