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Purple sulfur bacteria (PSB) are capable of anoxygenic photosynthesis via oxidizing reduced sulfur compounds and are considered key drivers of the sulfur cycle in a range of anoxic environments. In this study, we show that Allochromatium vinosum (a PSB species) is capable of autotrophic growth using pyrite as the electron and sulfur source. Comparative growth profile, substrate characterization, and transcriptomic sequencing data provided valuable insight into the molecular mechanisms underlying the bacterial utilization of pyrite and autotrophic growth. Specifically, the pyrite-supported cell cultures ("py"') demonstrated robust but much slower growth rates and distinct patterns from their sodium sulfide-amended positive controls. Up to ~200-fold upregulation of genes encoding various c- and b-type cytochromes was observed in "py," pointing to the high relevance of these molecules in scavenging and relaying electrons from pyrite to cytoplasmic metabolisms. Conversely, extensive downregulation of genes related to LH and RC complex components indicates that the electron source may have direct control over the bacterial cells' photosynthetic activity. In terms of sulfur metabolism, genes encoding periplasmic or membrane-bound proteins (e.g., FccAB and SoxYZ) were largely upregulated, whereas those encoding cytoplasmic proteins (e.g., Dsr and Apr groups) are extensively suppressed. Other notable differentially expressed genes are related to flagella/fimbriae/pilin(+), metal efflux(+), ferrienterochelin(-), and [NiFe] hydrogenases(+). Characterization of the biologically reacted pyrite indicates the presence of polymeric sulfur. These results have, for the first time, put the interplay of PSB and transition metal sulfide chemistry under the spotlight, with the potential to advance multiple fields, including metal and sulfur biogeochemistry, bacterial extracellular electron transfer, and artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Earlier, it was suggested that carotenoids in light-harvesting complexes 2 (LH2) can generate singlet oxygen, further oxidizing bacteriochlorophyll to 3-acetyl-chlorophyll. In the present work, it was found that illumination of isolated LH2 preparations of purple sulfur bacterium Ectothiorhodospira haloalkaliphila with light in the carotenoid absorption region leads to the photoconsumption of molecular oxygen, which is accompanied by the formation of hydroperoxides of organic molecules in the complexes. Photoformation of two types of organic hydroperoxides were revealed: highly lipophilic (12 molecules per one LH2) and relatively hydrophobic (68 per one LH2). It has been shown that illumination leads to damage to light-harvesting complexes. On the one hand, photobleaching of bacteriochlorophyll and a decrease in its fluorescence intensity are observed. On the other hand, the photoinduced increase in the hydrodynamic radius of the complexes, the reduction in their thermal stability, and the change in fluorescence intensity indicate conformational changes occurring in the protein molecules of the LH2 preparations. Inhibition of the processes described above upon the addition of singlet oxygen quenchers (L-histidine, Trolox, sodium L-ascorbate) may support the hypothesis that carotenoids in LH2 preparations are capable of generating singlet oxygen, which, in turn, damage to protein molecules.

The composition and structure of the anoxygenic phototrophic bacterial (APB) community in the water column of meromictic Lake Bol'shie Khruslomeny during winter were investigated. The community developed at the depth of 4.25 m, and its activity in the ice-cover period was very low (6.2 µmol C L–1 day–1). The water in the zone of highest development of phototrophic bacteria was of an unusual lemon-yellow color, probably due to the production and accumulation of polysulfides. The near-bottom water was also of lemon-yellow color and was resistant to oxidation by the air oxygen. In the zone of peak APB development the content of BChl d from green-colored green sulfur bacteria was considerably higher than that of BChl e from brown-colored green sulfur bacteria: 77 and 23%, respectively. The cultures of green and purple sulfur bacteria were isolated from lake water, and their physiological and genetic characteristics were determined. Two strains of green sulfur bacteria (brown-colored BrKhr17 and green-colored GrKhr17) contained gas vacuoles in their cells. Phylogenetically they were most closely related to the green-colored strain Chlorobium phaeovibrioides DSM 265 and were identified as new strains of the species Chlorobium phaeovibrioides. [ABSTRACT FROM AUTHOR]

In the pursuit of cultivating anaerobic anoxygenic phototrophs with unusual absorbance spectra, a purple sulfur bacterium was isolated from the shoreline of Baltrum, a North Sea island of Germany. It was designated strain 970, due to a predominant light harvesting complex (LH) absorption maximum at 963–966 nm, which represents the furthest infrared-shift documented for such complexes containing bacteriochlorophyll a. A polyphasic approach to bacterial systematics was performed, comparing genomic, biochemical, and physiological properties. Strain 970 is related to Thiorhodovibrio winogradskyi DSM 6702T by 26.5, 81.9, and 98.0% similarity via dDDH, ANI, and 16S rRNA gene comparisons, respectively. The photosynthetic properties of strain 970 were unlike other Thiorhodovibrio spp., which contained typical LH absorbing characteristics of 800–870 nm, as well as a newly discovered absorption band at 908 nm. Strain 970 also had a different photosynthetic operon composition. Upon genomic comparisons with the original Thiorhodovibrio strains DSM 6702T and strain 06511, the latter was found to be divergent, with 25.3, 79.1, and 97.5% similarity via dDDH, ANI, and 16S rRNA gene homology to Trv. winogradskyi, respectively. Strain 06511 (=DSM 116345T) is thereby described as Thiorhodovibrio litoralis sp. nov., and the unique strain 970 (=DSM 111777T) as Thiorhodovibrio frisius sp. nov. [ABSTRACT FROM AUTHOR]

When oxidizing reduced sulfur compounds, the phototrophic sulfur bacterium Allochromatium vinosum forms spectacular sulfur globules as obligatory intracellular–but extracytoplasmic–intermediates. The globule envelope consists of three extremely hydrophobic proteins: SgpA and SgpB, which are very similar and can functionally replace each other, and SgpC which is involved in the expansion of the sulfur globules. The presence of a fourth protein, SgpD, was suggested by comparative transcriptomics and proteomics of purified sulfur globules. Here, we investigated the in vivo function of SgpD by coupling its carboxy-terminus to mCherry. This fluorescent protein requires oxygen for chromophore maturation, but we were able to use it in anaerobically growing A. vinosum provided the cells were exposed to oxygen for one hour prior to imaging. While mCherry lacking a signal peptide resulted in low fluorescence evenly distributed throughout the cell, fusion with SgpD carrying its original Sec-dependent signal peptide targeted mCherry to the periplasm and co-localized it exactly with the highly light-refractive sulfur deposits seen in sulfide-fed A. vinosum cells. Insertional inactivation of the sgpD gene showed that the protein is not essential for the formation and degradation of sulfur globules. [ABSTRACT FROM AUTHOR]

Given the wide usage of Roundup, a common herbicide, the impacts of its presence in ecological communities are of great interest. Many studies have investigated the effects of glyphosate, the active ingredient in Roundup, on different factions of an ecosystem including on animals, plants, microorganisms, and nutrients. The current study expanded upon these works using Roundup instead of glyphosate to provide a realistic application in which to observe the development of microbial assemblages and nutrient composition in two different habitats. Winogradsky columns were prepared using benthic material from a ditch and a pond. Varying concentrations of Roundup were introduced to the columns at the beginning of the study and microbial growth and nutrient compositions from each column were measured weekly. The results indicate that the presence of Roundup has varying effects on microorganisms and nutrients. While photosynthetic microbes were negatively impacted, a shift in the microbial composition to heterotrophic microbes indicates that these microorganisms were able to utilize some ingredients in Roundup as a nutrient source. Additionally, the temporal analysis of nutrient compositions indicated that microbes metabolize glyphosate starting with the phosphate moiety even when the other compounds in Roundup are present. While these trends were observed in both benthic habitats, the composition of the ecological community can affect its ability to utilize the ingredients in Roundup as a nutrient source.

Several strains of a Gram-negative, anaerobic photoautotrophic, motile, rod-shaped bacterium, designated as B14B, A-7R, and A-7Y were isolated from biofilms of low-mineralized soda lakes in central Mongolia and Russia (southeast Siberia). They had lamellar stacks as photosynthetic structures and bacteriochlorophyll a as the major photosynthetic pigment. The strains were found to grow at 25–35 °C, pH 7.5–10.2 (optimum, pH 9.0), and with 0–8% (w/v) NaCl (optimum, 0%). In the presence of sulfide and bicarbonate, acetate, butyrate, yeast extract, lactate, malate, pyruvate, succinate, and fumarate promoted growth. The DNA G + C content was 62.9–63.0 mol%. While the 16S rRNA gene sequences confirmed that the new strains belonged to the genus Ectothiorhodospira of the Ectothiorhodospiraceae, comparison of the genome nucleotide sequences of strains B14B, A-7R, and A-7Y revealed that the new isolates were remote from all described Ectothiorhodospira species both in dDDH (19.7–38.8%) and in ANI (75.0–89.4%). The new strains are also genetically differentiated by the presence of a nitric oxide reduction pathway that is lacking from all other Ectiothiorhodospiraceae. We propose to assign the isolates to the new species, Ectothiorhodospira lacustris sp. nov., with the type strain B14BT (=DSM 116064T = KCTC 25542T = UQM 41491T). [ABSTRACT FROM AUTHOR]

In this study, three metagenome-assembled genomes of a sediment sample were constructed. A Bin1 (JB001) genome was identified as a photo-litho-auto/heterotroph (purple sulfur bacteria) bacterium with the ability to fix nitrogen, tolerate salt, and to produce bacteriochlorophyll a. It has a genome length of 4.1 Mb and a G + C content of 64.9%. Phylogenetic studies based on concatenated 92 core genes and photosynthetic genes (pufLM and bchY) showed that Bin JB001 is related to Thiococcus pfennigii, "Thioflavicoccus mobilis" and to the Lamprocystis purpurea lineage. Bin JB001 and its closely related members were subjected to the genome-based study of phenotypic and phylogenomic analysis. Genomic similarity indices (dDDH and ANI) showed that Bin JB001 could be defined as a novel species. The average amino acid identity (AAI) and percentage of conserved proteins (POCP) values were below 60 and 50%, respectively. The pan-genome analysis indicated that the pan-genome was an open type wherein Bin JB001 had 855 core genes. This study shows that the binned genome, Bin JB001 could represent a novel species of a new genus under the family Chromatiaceae, for which the name "Candidatus Thioaporhodococcus sediminis" gen. nov. sp. nov. is proposed. [ABSTRACT FROM AUTHOR]

Given the wide usage of Roundup, a common herbicide, the impacts of its presence in ecological communities are of great interest. Many studies have investigated the effects of glyphosate, the active ingredient in Roundup, on different factions of an ecosystem including on animals, plants, microorganisms, and nutrients. The current study expanded upon these works using Roundup instead of glyphosate to provide a realistic application in which to observe the development of microbial assemblages and nutrient composition in two different habitats. Winogradsky columns were prepared using benthic material from a ditch and a pond. Varying concentrations of Roundup were introduced to the columns at the beginning of the study and microbial growth and nutrient compositions from each column were measured weekly. The results indicate that the presence of Roundup has varying effects on microorganisms and nutrients. While photosynthetic microbes were negatively impacted, a shift in the microbial composition to heterotrophic microbes indicates that these microorganisms were able to utilize some ingredients in Roundup as a nutrient source. Additionally, the temporal analysis of nutrient compositions indicated that microbes metabolize glyphosate starting with the phosphate moiety even when the other compounds in Roundup are present. While these trends were observed in both benthic habitats, the composition of the ecological community can affect its ability to utilize the ingredients in Roundup as a nutrient source. [ABSTRACT FROM AUTHOR]

The mechanism of bacteriochlorophyll photooxidation in light-harvesting complexes of a number of purple photosynthetic bacteria when the complexes are excited into the carotenoid absorption bands remains unclear for many years. Here, using narrow-band laser illumination we measured action spectrum of this process for the spectral ranges of carotenoid and bacteriochlorophyll. It is shown that bacteriochlorophyll excitation results in almost no photooxidation of these molecules, while carotenoid excitation leads to oxidation with quantum yield of about 0,0003. Low value of the yield enabled an assumption that the studied process is initiated by the triplet states of the main carotenoids of the complexes with the number of conjugated double-bond chain length of N = 11. Interaction of these states with oxygen facilitates formation, though with low efficiency, of the excited singlet oxygen, which oxidizes bacteriochlorophylls. The carotenoid triplet states are formed in the process of the earlier studied singlet-triplet fission. The obtained results point at the necessity of reconsidering the functions of carotenoids in the light-harvesting complexes of purple bacteria. [ABSTRACT FROM AUTHOR]

In the pursuit of cultivating anaerobic anoxygenic phototrophs with unusual absorbance spectra, a purple sulfur bacterium was isolated from the shoreline of Baltrum, a North Sea island of Germany. It was designated strain 970, due to a predominant light harvesting complex (LH) absorption maximum at 963–966 nm, which represents the furthest infrared-shift documented for such complexes containing bacteriochlorophyll a. A polyphasic approach to bacterial systematics was performed, comparing genomic, biochemical, and physiological properties. Strain 970 is related to Thiorhodovibrio winogradskyi DSM 6702T by 26.5, 81.9, and 98.0% similarity via dDDH, ANI, and 16S rRNA gene comparisons, respectively. The photosynthetic properties of strain 970 were unlike other Thiorhodovibrio spp., which contained typical LH absorbing characteristics of 800–870 nm, as well as a newly discovered absorption band at 908 nm. Strain 970 also had a different photosynthetic operon composition. Upon genomic comparisons with the original Thiorhodovibrio strains DSM 6702T and strain 06511, the latter was found to be divergent, with 25.3, 79.1, and 97.5% similarity via dDDH, ANI, and 16S rRNA gene homology to Trv. winogradskyi, respectively. Strain 06511 (=DSM 116345T) is thereby described as Thiorhodovibrio litoralis sp. nov., and the unique strain 970 (=DSM 111777T) as Thiorhodovibrio frisius sp. nov.

When oxidizing reduced sulfur compounds, the phototrophic sulfur bacterium Allochromatium vinosum forms spectacular sulfur globules as obligatory intracellular–but extracytoplasmic–intermediates. The globule envelope consists of three extremely hydrophobic proteins: SgpA and SgpB, which are very similar and can functionally replace each other, and SgpC which is involved in the expansion of the sulfur globules. The presence of a fourth protein, SgpD, was suggested by comparative transcriptomics and proteomics of purified sulfur globules. Here, we investigated the in vivo function of SgpD by coupling its carboxy-terminus to mCherry. This fluorescent protein requires oxygen for chromophore maturation, but we were able to use it in anaerobically growing A. vinosum provided the cells were exposed to oxygen for one hour prior to imaging. While mCherry lacking a signal peptide resulted in low fluorescence evenly distributed throughout the cell, fusion with SgpD carrying its original Sec-dependent signal peptide targeted mCherry to the periplasm and co-localized it exactly with the highly light-refractive sulfur deposits seen in sulfide-fed A. vinosum cells. Insertional inactivation of the sgpD gene showed that the protein is not essential for the formation and degradation of sulfur globules.

Several strains of a Gram-negative, anaerobic photoautotrophic, motile, rod-shaped bacterium, designated as B14B, A-7R, and A-7Y were isolated from biofilms of low-mineralized soda lakes in central Mongolia and Russia (southeast Siberia). They had lamellar stacks as photosynthetic structures and bacteriochlorophyll a as the major photosynthetic pigment. The strains were found to grow at 25–35 °C, pH 7.5–10.2 (optimum, pH 9.0), and with 0–8% (w/v) NaCl (optimum, 0%). In the presence of sulfide and bicarbonate, acetate, butyrate, yeast extract, lactate, malate, pyruvate, succinate, and fumarate promoted growth. The DNA G + C content was 62.9–63.0 mol%. While the 16S rRNA gene sequences confirmed that the new strains belonged to the genus Ectothiorhodospira of the Ectothiorhodospiraceae, comparison of the genome nucleotide sequences of strains B14B, A-7R, and A-7Y revealed that the new isolates were remote from all described Ectothiorhodospira species both in dDDH (19.7–38.8%) and in ANI (75.0–89.4%). The new strains are also genetically differentiated by the presence of a nitric oxide reduction pathway that is lacking from all other Ectiothiorhodospiraceae. We propose to assign the isolates to the new species, Ectothiorhodospira lacustris sp. nov., with the type strain B14BT (=DSM 116064T = KCTC 25542T = UQM 41491T).

We describe a new species of purple sulfur bacteria (Chromatiaceae, anoxygenic phototrophic bacteria) isolated from a microbial mat in the sulfidic geothermal outflow of a hot spring in Rotorua, New Zealand. This phototroph, designated as strain NZ, grew optimally near 45 °C but did not show an absorption maximum at 915 nm for the light-harvesting-reaction center core complex (LH1-RC) characteristic of other thermophilic purple sulfur bacteria. Strain NZ had a similar carotenoid composition as Thermochromatium tepidum, but unlike Tch. tepidum, grew photoheterotrophically on acetate in the absence of sulfide and metabolized thiosulfate. The genome of strain NZ was significantly larger than that of Tch. tepidum but slightly smaller than that of Allochromatium vinosum. Strain NZ was phylogenetically more closely related to mesophilic purple sulfur bacteria of the genus Allochromatium than to Tch. tepidum. This conclusion was reached from phylogenetic analyses of strain NZ genes encoding 16S rRNA and the photosynthetic functional gene pufM, from phylogenetic analyses of entire genomes, and from a phylogenetic tree constructed from the concatenated sequence of 1090 orthologous proteins. Moreover, average nucleotide identities and digital DNA:DNA hybridizations of the strain NZ genome against those of related species of Chromatiaceae supported the phylogenetic analyses. From this collection of properties, we describe strain NZ here as the first thermophilic species of the genus Allochromatium, Allochromatium tepidum NZT, sp. nov. [ABSTRACT FROM AUTHOR]

The complete genome sequence of the thermophilic purple sulfur bacterium Thermochromatium tepidum strain MCT (DSM 3771T) is described and contrasted with that of its mesophilic relative Allochromatium vinosum strain D (DSM 180T) and other Chromatiaceae. The Tch. tepidum genome is a single circular chromosome of 2,958,290 base pairs with no plasmids and is substantially smaller than the genome of Alc. vinosum. The Tch. tepidum genome encodes two forms of RuBisCO and contains nifHDK and several other genes encoding a molybdenum nitrogenase but lacks a gene encoding a protein that assembles the Fe–S cluster required to form a functional nitrogenase molybdenum-iron cofactor, leaving the phototroph phenotypically Nif–. Tch. tepidum contains genes necessary for oxidizing sulfide to sulfate as photosynthetic electron donor but is genetically unequipped to either oxidize thiosulfate as an electron donor or carry out assimilative sulfate reduction, both of which are physiological hallmarks of Alc. vinosum. Also unlike Alc. vinosum, Tch. tepidum is obligately phototrophic and unable to grow chemotrophically in darkness by respiration. Several genes present in the Alc. vinosum genome that are absent from the genome of Tch. tepidum likely contribute to the major physiological differences observed between these related purple sulfur bacteria that inhabit distinct ecological niches. [ABSTRACT FROM AUTHOR]

ABSTRACT In summer 2019, a large, bright pink microbial mat was visible on top of macroalgal deposits in muddy sediments of an urban beach (Playa do Adro, Vigo). In order to characterize the dominant organisms in these colored mats, results from microscopic observations, photosynthetic pigments, and molecular analysis were gathered. Light microscopy examination revealed pinkish microbial aggregates with minor contributions of larger protists and cyanobacteria. High-performance liquid chromatography (HPLC) pigment analysis documented the dominance of bacteriochlorophyll a and carotenoids whose spectra were compatible with those described in photosynthetic purple bacteria. 16S rRNA gene amplicon sequencing confirmed that the vast majority of reads belonged to Proteobacteria (73.5%), and among them, nearly 88% of those reads belonged to purple sulfur bacteria (Gammaproteobacteria). A single family, Chromatiaceae, constituted the bulk of this assemblage, including the genera Thiohalocapsa (32%), Marichromatium (12.5%), Phaeochromatium (5%), and Halocromatium (2%) as main contributors. Nonetheless, a considerable number of sequences could not be assigned to a particular genus, stressing the large biological diversity in these microbial mats and the potential presence of novel taxa of purple sulfur bacteria. IMPORTANCE Urban beaches are valuable recreational areas particularly vulnerable to human disturbance. In these areas, the intertidal sediments harbor a diverse community of microorganisms, including virus, bacteria, fungi, and protozoa. In this sense, pollution events can introduce pathogenic allochthonous microbes which may constitute a human health risk. Visual and sensory observations, such as a weird color or bad smell, are usually appreciated as a warning by beachgoers and authorities, as indeed was the case at do Adro beach in 2019. The observed proliferation seems to be common in summertime, but its dimension alerted beachgoers and media. The obtained results allowed for the identification of purple sulfur bacteria as responsible for the pink-violet top layer staining the intertidal zone. These blooms have never been associated with public health risks. Beyond solving the sanitary concern, other important findings were its diversity and large proportion of novel taxa, illustrating the complexity of these ecosystems.

The review considers the role of purple sulfur bacteria in the global cycles of hydrogen and sulfur, as well as the ecology and physiology of these bacteria in relation to the metabolism of sulfur and hydrogen. Information is presented on five types of hydrogenases involved in consumption or production of hydrogen, as well as on various enzymes involved in the oxidation/reduction of sulfur compounds. Advances in the biochemistry and genetics of the enzymes from these microorganisms make it possible to analyze the interconnection of processes at a new level. [ABSTRACT FROM AUTHOR]

Lake Uchum is a newly defined meromictic lake in Siberia with clear seasonal changes in its mixolimnion. This study characterized the temporal dynamics and vertical profile of bacterial communities in oxic and anoxic zones of the lake across all four seasons: October (autumn), March (winter), May (spring), and August (summer). Bacterial richness and diversity in the anoxic zone varied widely between time points. Proteobacteria was the dominant bacterial phylum throughout the oxic and anoxic zones across all four seasons. Alphaproteobacteria (Loktanella) and Gammaproteobacteria (Aliidiomarina) exhibited the highest abundance in the oxic and anoxic zone, respectively. Furthermore, there was a successional shift in sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria in the anoxic zone across the seasons. The most dominant SRB, Desulfonatronovibrio sp., is likely one of the main producers of hydrogen sulfide (H2S) and typically accumulates the most H2S in winter. The representative anoxygenic phototrophic bacterial group in Lake Uchum was purple sulfur bacteria (PSB). PSB were dominant (60.76%) in summer, but only had 0.2–1.5% relative abundance from autumn to spring. Multivariate analysis revealed that the abundance of these SRB and PSB correlated to the concentration of H2S in Lake Uchum. Taken together, this study provides insights into the relationships between changes in bacterial community and environmental features in Lake Uchum. [ABSTRACT FROM AUTHOR]

In a conserved culture of the purple sulfur bacterium Thiospirillum jenense DSM216T, cells of this species were easily recognized by cell morphology, large-size spirilla and visible flagellar tuft. The Tsp. jenense genome is 3.22 Mb in size and has a GC content of 48.7 mol%. It was readily identified as a member of the Chromatiaceae by the complement of proteins in its genome. A whole genome comparison clearly placed Tsp. jenense near Thiorhodovibrio and Rhabdochromatium species and somewhat more distant from Thiohalocapsa and Halochromatium species. This relationship was also found with the sequences of the photosynthetic reaction center protein PufM. The genome sequence supported important properties of this bacterium: the presence of ribulose-bisphosphate carboxylase and enzymes of the Calvin cycle of autotrophic carbon dioxide fixation but the absence of carboxysomes, an incomplete tricarboxylic acid cycle and the lack of malate dehydrogenase, the presence of a sulfur oxidation pathway including adenylylsulfate reductase (aprAB) but absence of assimilatory sulfate reduction, the presence of hydrogenase (hoxHMFYUFE), nitrogenase and a photosynthetic gene cluster (pufBALMC). The FixNOP type of cytochrome oxidase was notably lacking, which may be the reason that renders the cells highly sensitive to oxygen. Two minor phototrophic contaminants were found using metagenomic binning: one was identified as a strain of Rhodopseudomonas palustris and the second one has an average nucleotide identity of 82% to the nearest neighbor Rhodoferax antarcticus. It should be considered as a new species of this genus and Rhodoferax jenense is proposed as the name. [ABSTRACT FROM AUTHOR]

The Ectothiorhodospiraceae family represents purple sulfur bacteria of the Gammaproteobacteria found primarily in alkaline soda lakes of moderate to extremely high salinity. The main microscopically visible characteristic separating them from the Chromatiaceae is the excretion of the intermediate elemental sulfur formed during oxidation of sulfide prior to complete oxidation to sulfate rather than storing it in the periplasm. We present a comparative study of 38 genomes of all species of phototrophic Ectothiorhodospiraceae. We also include a comparison with those chemotrophic bacteria that have been assigned to the family previously and critically reevaluate this assignment. The data demonstrate the separation of Halorhodospira species in a major phylogenetic branch distant from other Ectothiorhodospiraceae and support their separation into a new family, for which the name Halorhodospiraceae fam. nov. is proposed. In addition, the green-colored, bacteriochlorophyll-containing species Halorhodospira halochloris and Halorhodospira abdelmalekii were transferred to the new genus Halochlorospira gen. nov. of this family. The data also enable classification of several so far unclassified isolates and support the separation of Ectothiorhodospira shaposhnikovii and Ect. vacuolata as well as Ect. mobilis and Ect. marismortui as distinct species.

Forecasting the abundance of phototrophic sulfur bacteria in lakes is very important because 1) these bacteria are major consumers of hydrogen sulfide, and 2) fossil carotenoids of these bacteria are retrospective biomarkers of limnological conditions. Therefore, understanding the factors controlling the dynamics of the abundance of phototrophic sulfur bacteria in a lake is necessary both for the prediction of hydrogen sulfide content and for paleo-limnological reconstruction. Based on long-term monitoring of the abundance of purple sulfur bacteria (PSB) in the saline meromictic Lake Shira (South Siberia, Khakassia), we proposed a hypothesis that relatively small changes in water temperature in the cold deep chemocline affect the PSB abundance in the lake. We tested this hypothesis experimentally. The purple sulfur bacterium Thiocapsa sp. Shira_1 (Chromatiaceae) from Lake Shira (South Siberia, Russia) was grown on a sulfide-containing synthetic medium under anoxic conditions in batch culture at low temperatures, from -1ºC to +8ºC, which were similar to in situ temperatures observed in the chemocline of Lake Shira. The cell growth rate at +8ºC was similar to the growth rate at room temperature, whereas there was no growth at -1ºC and +5ºC. Therefore, the variations in the biomass of purple sulfur bacteria (PSB) observed in Lake Shira could be caused by variations in chemocline temperature. The high correlation between chemocline temperature and PSB biomass supported this conclusion

Long-term measurements show that the sedimentation dynamics of okenone (a carotenoid of purple sulfur bacteria) reflects the abundance of purple sulfur bacteria, the hydrogen sulfide content, and the stratification stability in the closed saline meromictic Shira Lake (Southern Siberia, Russia). The profile of fossil okenone in bottom sediments has been compared with the data on the water surface level in the lake over the last 100 years. The peaks of okenone correspond to lake transgressions, and the drops in the okenone content coincide with periods of stable or decreasing water level. Our observations show that fossil okenone may be used as a qualitative proxy of meromictic conditions and as a quantitative proxy of the water level dynamics in closed stratified lakes. Therefore, okenone can be used for qualitative reconstructions of the water balance and climate humidity in arid zones. [ABSTRACT FROM AUTHOR]

Earlier, it was suggested that carotenoids in light-harvesting complexes 2 (LH2) can generate singlet oxygen, further oxidizing bacteriochlorophyll to 3-acetyl-chlorophyll. In the present work, it was found that illumination of isolated LH2 preparations of purple sulfur bacterium Ectothiorhodospira haloalkaliphila with light in the carotenoid absorption region leads to the photoconsumption of molecular oxygen, which is accompanied by the formation of hydroperoxides of organic molecules in the complexes. Photoformation of two types of organic hydroperoxides were revealed: highly lipophilic (12 molecules per one LH2) and relatively hydrophobic (68 per one LH2). It has been shown that illumination leads to damage to light-harvesting complexes. On the one hand, photobleaching of bacteriochlorophyll and a decrease in its fluorescence intensity are observed. On the other hand, the photoinduced increase in the hydrodynamic radius of the complexes, the reduction in their thermal stability, and the change in fluorescence intensity indicate conformational changes occurring in the protein molecules of the LH2 preparations. Inhibition of the processes described above upon the addition of singlet oxygen quenchers (L-histidine, Trolox, sodium L-ascorbate) may support the hypothesis that carotenoids in LH2 preparations are capable of generating singlet oxygen, which, in turn, damage to protein molecules., Competing Interests: The authors declare there are no competing interests., (©2024 Yanykin et al.)

The thermophilic purple sulfur bacterium Thermochromatium tepidum possesses four main water-soluble redox proteins involved in the electron transfer behavior. Crystal structures have been reported for three of them: a high potential iron-sulfur protein, cytochrome c′, and one of two low-potential cytochrome c552 (which is a flavocytochrome c) have been determined. In this study, we purified another low-potential cytochrome c552 (LPC), determined its N-terminal amino acid sequence and the whole gene sequence, characterized it with absorption and electron paramagnetic spectroscopy, and solved its high-resolution crystal structure. This novel cytochrome was found to contain five c-type hemes. The overall fold of LPC consists of two distinct domains, one is the five heme-containing domain and the other one is an Ig-like domain. This provides a representative example for the structures of multiheme cytochromes containing an odd number of hemes, although the structures of multiheme cytochromes with an even number of hemes are frequently seen in the PDB database. Comparison of the sequence and structure of LPC with other proteins in the databases revealed several characteristic features which may be important for its functioning. Based on the results obtained, we discuss the possible intracellular function of this LPC in Tch. tepidum. [ABSTRACT FROM AUTHOR]

Marine cyanobacterial mats were cultured on coastal sediments (Nivå Bay, Øresund, Denmark) for over three years in a closed system. Carbonate particles formed in two different modes in the mat: (i) through precipitation of submicrometer-sized grains of Mg calcite within the mucilage near the base of living cyanobacterial layers, and (ii) through precipitation of a variety of mixed Mg calcite/aragonite morphs in layers of degraded cyanobacteria dominated by purple sulfur bacteria. The d13C values were about 2‰ heavier in carbonates from the living cyanobacterial zones as compared to those generated in the purple bacterial zones. Saturation indices calculated with respect to calcite, aragonite, and dolomite inside the mats showed extremely high values across the mat profile. Such high values were caused by high pH and high carbonate alkalinity generated within the mats in conjunction with increased concentrations of calcium and magnesium that were presumably stored in sheaths and extracellular polymer substances (EPS) of the living cyanobacteria and liberated during their post-mortem degradation. The generated CaCO3 morphs were highly similar to morphs reported from heterotrophic bacterial cultures, and from bacterially decomposed cyanobacterial biomass emplaced in Ca-rich media. They are also similar to CaCO3 morphs precipitated from purely inorganic solutions. No metabolically (enzymatically) controlled formation of particular CaCO3 morphs by heterotrophic bacteria was observed in the studied mats. The apparent alternation of in vivo and post-mortem generated calcareous layers in the studied cyanobacterial mats may explain the alternation of fine-grained (micritic) and coarse-grained (sparitic) laminae observed in modern and fossil calcareous cyanobacterial microbialites as the result of a probably similar multilayered mat organization.

Traditional methods to combat disease with antimicrobial agents in aquaculture have caused serious concern and alternative approaches using probiotics have been sought. A photosynthetic purple sulfur bacteria Marichromatium purpuratum RuA2 that thrives at salt concentrations of 0.5% to 5.0% and has a more temperate tolerance for oxygen was isolated from a marine fish pond located on the southwestern shore of Qigu, Taiwan. The effects of M. purpuratum RuA2 on the water quality parameters, the occurrence of the sulfonamide resistance gene sul1 and the microbial community were investigated in situ. Supplementation with strain RuA2 resulted in an increased removal rate of total organic carbon and nitrate ions, as well as a lower occurrence of sul1 , in the bacterial community. The abundance and diversity of the bacterial community in the control and M. purpuratum RuA2 -supplemented water samples were investigated. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Planctomycetes were identified to be the top five predominant phyla in the control and M. purpuratum RuA2-supplemented water samples. However, supplementation with M. purpuratum RuA2 increased the diversity of the bacterial community composition. Fourteen unique genera were detected solely in strain RuA2-supplemented water samples and the relative abundance of seven shared genera was associated with supplementation with strain RuA2. In conclusion, M. purpuratum RuA2 showed a desirable capacity for improving water quality, reducing the occurrence of the resistance gene sul1 and advantageous effects on the microbial community structure. Tolerant to salinity and oxygen, M. purpuratum RuA2 exhibits an attractive potential for resolving the challenges facing aquaculture today. [ABSTRACT FROM AUTHOR]

Abstract: The carbon and nitrogen isotopic signatures of chloropigments and porphyrins from the sediments of redox‐stratified lakes and marine basins reveal details of past biogeochemical nutrient cycling. Such interpretations are strengthened by modern calibration studies, and here, we report on the C and N isotopic composition of pigments and nutrients in the water column and surface sediment of redox‐stratified Fayetteville Green Lake (FGL; New York). We also report δ13C and δ15N values for pyropheophytin a (Pphe a) and bacteriochlorophyll e (Bchl e) deposited in the Black Sea during its transition to a redox‐stratified basin ca. 7.8 ka. We propose a model for evolving nutrient cycling in the Black Sea from 7.8 to 6.4 ka, informed by the new pigment data from FGL. The seasonal study of water column nutrients and pigments at FGL revealed population dynamics in surface and deep waters that were also captured in the sediments. Biomass was greatest near the chemocline, where cyanobacteria, purple sulfur bacteria (PSB), and green sulfur bacteria (GSB) had seasonally variable populations. Bulk organic matter in the surface sediment, however, was derived mainly from the oxygenated surface waters. Surface sediment pigment δ13C and δ15N values indicate intact chlorophyll a (Chl a) was derived from near the chemocline, but its degradation product pheophytin a (Phe a) was derived primarily from surface waters. Bacteriopheophytin a (Bphe a) and Bchl e in the sediments came from chemocline populations of PSB and GSB, respectively. The distinctive δ13C and δ15N values for Chl a, Phe a, and Bphe a in the surface sediment are inputs to an isotopic mixing model that shows their decomposition to a common porphyrin derivative can produce non‐specific sedimentary isotope signatures. This model serves as a caveat for paleobiogeochemical interpretations in basins that had diverse populations near a shallow chemocline. [ABSTRACT FROM AUTHOR]

Sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria drive major transformations in the sulfur cycle, and play vital roles in oxic--anoxic transitions in lakes and coastal waters. However, information on the succession of these sulfur bacteria in seasonally stratified lakes using molecular biological techniques is scarce. Here, we used 16S rRNA gene amplicon sequencing to study the spatio-temporal dynamics of sulfur bacteria during oxic--anoxic regime shifts in Lake Vechten. Oxygen and sulfate were mixed throughout the water column in winter and early spring. Meanwhile, SRB, green sulfur bacteria (GSB), purple sulfur bacteria (PSB), and colorless sulfur bacteria (CSB) exclusively inhabited the sediment. After the water column stratified, oxygen and nitrate concentrations decreased in the hypolimnion and various SRB species expanded into the anoxic hypolimnion. Consequently, sulfate was reduced to sulfide, stimulating the growth of PSB and GSB in the metalimnion and hypolimnion during summer stratification. When hypoxia spread throughout the water column during fall turnover, SRB and GSB vanished from the water column, whereas CSB (mainly Arcobacter) and PSB (Lamprocystis) became dominant and oxidized the accumulated sulfide under micro-aerobic conditions. Our results support the view that, once ecosystems have become anoxic and sulfidic, a large oxygen influx is needed to overcome the anaerobic sulfur cycle and bring the ecosystems back into their oxic state. [ABSTRACT FROM AUTHOR]

Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a , organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira. [ABSTRACT FROM AUTHOR]

The phototrophic bacteria were isolated from water and silt of Saki lake (AR Crimea). The were brown-red coloured. This bacteria used hydrogen sulfide in anaerobic photosyntetical process and stored elemental sulfur inside the cells. According to physiological, biochemical, morphological properties, this bacteria was ascribed to Chromatiaceaе family. The 16S DNA gene sequence analysis based on using Blastn program revealed that investigated consecution has 94% similarity to Thiohalocapsa halophila, Thiorhodococcus bheemlicus, Marinimicrobium koreense, Marichromatium bheemlicum, and 93% similarity to Thiorhodococcus minor, Thiorhodovibrio winogradsky of Gammaproteo­bacteria domein. Based on the study of morphological, physiological characteristics and 16S rRNA nucleotide gene sequences, phototrophic purple bacteria of Sа-2010/А strain from water of Saki lake (AR Crimea) belong to Thiorhodococcus genus.

The photosynthetic purple sulfur bacteria were isolated from lakes Yavorivske (Lviv region) and Sakske (AR Crimea). The purple sulfur bacteria use reduced sulfur compounds as electron donors for anoxygenic photosynthesis. The elemental sulfur produced by these microorganisms as intermediate in the oxidation of thiosulfate or hydrogen sulfide to sulfate. The bacteria strains Ya2008/С and Sa2008/D with highest intracellular sulfur content have been choose for next investigation. Their morphophysiology characteristics, pigment content, the resistances to hydrogen sulfide, utilization of H2S and intracellular sulfur during photolitoautotrophic growth were investigated. Strains Ya2008/С and Sa2008/D according to their morphophysiology characteristics were identified to genus Chromatium.

The ability of the purple sulfur bacteria Thiocapsa sp. to use acetate and pyruvate in the anoxygenic photosyntetical process was studied. We assume that Thiocapsa sp. able to carry photoorganoheterotrophic way of life, because of investigated bacteria grew well on the medium with organic components in a presence of sulfide as electron donor and when it wasn’t added. The dynamics of intracellular sulfur content changes was observed. A high removablility of value of reserved sulfur in cells was revealed. The highest sulfur content Thiocapsa sp. was in cells when bacteria grew photolitoautotrophically and photolitoheterotrophically.