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Cyanobacteria are some of the primary producers in extremely cold biospheres such as the Arctic, Antarctic, and vast ice sheets. Many genera of cyanobacteria are identified from these harsh environments, but their specific mechanisms for cold adaptation are not fully understood. Nostoc sp. strain SO-36 is a cyanobacterium isolated in Antarctica more than 30 years ago and regarded as a psychrotolelant species. To determine whether the strain is psychrotolelant or psychrophilic, it was first grown at 30 °C and 10 °C. The cells grew exponentially at 30 °C, but their growth stopped at 10 °C, indicating that the strain is only psychrotolerant. Microscopic analysis revealed that the morphology of the cells grown at 30 °C was filamentous and differentiated heterocysts, which are specialized cells for gaseous nitrogen fixation under nitrogen-deprived conditions, indicating that the strain can grow diazotrophically. The cells grown at 10 °C have a smaller size, shortened filament length and decreased chlorophyll content per cell. At 10 °C, the cells are aggregated with extracellular polymeric substrates (EPSs), which is a common mechanism to protect cells from ultraviolet light. These results imply that segmentation into short filaments was induced by photodamage at low temperatures. To fully understand the adaptation mechanisms of Nostoc sp. strain SO-36 for low-temperature conditions, next-generation sequencing analyses were conducted. Complete genome sequence of the strain revealed that it has one main chromosome of approximately 6.8 Mbp with 4 plasmids, including 6855 coding sequences, 48 tRNA genes, 4 copies of rRNA operons, and 5 CRISPR regions. Putative genes for EPS biosynthesis were found to be conserved in Nostocaceae regardless of their habitat. These results provide basic information to understand the adaptation mechanisms at low temperatures, and the strain can be a model organism to analyze adaptation to extreme environments.

Currently, there are only six species in the genus Seonamhaeicola, i.e., Seonamhaeicola aphaedonensis, S. algicola, S. marinus, S. acroporae, S. maritimus, and S. sediminis. These bacteria have typical yellow or orange color. Among the identified strains, only S. marinus that had been reported to have a yellow polyene flexirubin pigment. However, the presence of carotenoid pigments has not been reported in this genus. Recently, we successfully isolated a new strain, S. algicola strain CC1, bacterium that was found in association with a red seaweed, Halymenia sp., collected from the coast of South Malang, Indonesia. The strain was grown well in the Zobell marine agar 2216E producing yellowish pigments. According to the 16S rRNA sequencing analysis and BLAST search, the strain is closely related to S. algicola strain Gy8, with 99.78% identity. The pigment composition was separated and analyzed by a high-performance liquid chromatography with tandem mass spectrometry detection (HPLC-MS/MS) and the strain was found to produce zeaxanthin as the major component, which appeared at a retention time (tR) of 28.89 min, showing a typical mass spectrum with a molecular ion at m/z 568.5 [M]+ and four product ions at m/z 261.4 [M−307]+, 476.6 [M−92]+, 429.3 [M−139]+, and 536.5 [M− 32]+. Other carotenoids, including zeaxanthin cis isomers, β-cryptoxanthin, β-carotene cis isomer, and β-carotene, are as minor components. The novel and noteworthy finding of this report is the identification of a Seonamhaeicola species that produces carotenoids and can be used as a source of zeaxanthin.

The lipid composition of thylakoid membranes is conserved from cyanobacteria to green plants. However, the biosynthetic pathways of galactolipids, the major components of thylakoid membranes, are known to differ substantially between cyanobacteria and green plants. We previously reported on a transformant of the unicellular rod-shaped cyanobacterium Synechococcus elongatus PCC 7942, namely SeGPT, in which the synthesis pathways of the galactolipids monogalactosyldiacylglycerol and digalactosyldiacylglycerol are completely replaced by those of green plants. SeGPT exhibited increased galactolipid content and could grow photoautotrophically, but its growth rate was slower than that of wild-type S. elongatus PCC 7942. In the present study, we investigated pleiotropic effects that occur in SeGPT and determined how its increased lipid content affects cell proliferation. Microscopic observations revealed that cell division and thylakoid membrane development are impaired in SeGPT. Furthermore, physiological analyses indicated that the bioenergetic state of SeGPT is altered toward energy storage, as indicated by increased levels of intracellular ATP and glycogen. We hereby report that we have identified a new promising candidate as a platform for material production by modifying the lipid synthesis system in this way.

Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the major components of thylakoid membranes and well-conserved from cyanobacteria to chloroplasts. However, cyanobacteria and chloroplasts synthesize these galactolipids using different pathways and enzymes, but they are believed to share a common ancestor. This fact implies that there was a replacement of the cyanobacterial galactolipid biosynthesis pathway during the evolution of a chloroplast. In this study, we first replaced the cyanobacterial MGDG biosynthesis pathway in a model cyanobacterium, Synechococcus elongatus PCC 7942, with the corresponding plant-type pathway. No obvious phenotype was observed under the optimum growth condition, and the content of membrane lipids was not largely altered in the transformants. We next replaced the cyanobacterial DGDG biosynthesis pathway with the corresponding plant-type pathway using the strain described above and isolated the strain harboring the replaced plant-type pathway instead of the whole galactolipid biosynthesis pathway. This transformant, SeGPT, can grow photoautotrophically, indicating that cyanobacterial galactolipid biosynthesis pathways can be functionally complemented by the corresponding plant-type pathways and that the lipid products MGDG and DGDG, and not biosynthesis pathways, are important. While SeGPT does not show strong growth retardation, the strain has low cellular chlorophyll content but it retained a similar oxygen evolution rate per chlorophyll content compared with the wild type. An increase in total membrane lipid content was observed in SeGPT, which was caused by a significant increase in DGDG content. SeGPT accumulated carotenoids from the xanthophyll groups. These results suggest that cyanobacteria have the capacity to accept other pathways to synthesize essential components of thylakoid membranes.

Heterocysts are the specialized cells for nitrogen fixation in some filamentous cyanobacteria. To protect the oxygen labile nitrogen fixing enzyme, nitrogenase, heterocysts keep their inner environment microoxic by developing layers of barrier on the outside of their outer membranes. Heterocyst specific glycolipids (Hgls) are constituents of the layer of barrier and amphipathic compounds, synthesized from a very long chain fatty alcohol as a hydrophobic tail and a sugar as a polar head. In the model heterocystous cyanobacterium Anabaena sp. PCC 7120, Hgls are made of fatty alcohol with 26 carbons and a glucose, linked by an ether bond in alpha configuration. The fatty alcohol is synthesized via reactions of a polyketide synthase, HglEA. In Anabaena sp. PCC 7120, another polyketide synthase HglE2 shared more than 50% identity in an amino acid sequence with HglEA and is expected to be involved in Hgls synthesis. However, no direct evidence has been reported. Here, we experimentally show that HglEA is the contributor of Hgls synthesis, and that HglE2 is not involved in the development of the heterocyst specific glycolipid layer.

Algae are ecologically important organisms and are widely used for basic research, with a focus on for example photosynthesis, evolution, and lipid metabolism. Many biosynthetic pathways of algal lipids have been deciphered using available genomic information. Here we describe methods for lipid analyses from three representative algae, including Archaeplastida, the SAR lineage (Stramenopiles, Alveolata, Rhizaria), and Excavata. Archaeplastida acquired their plastids by primary endosymbiosis, and the others by secondary endosymbiosis with a Rhodophyceae-type plastid in SAR and a Chlorophyceae-type plastid in Excavata (Euglenozoa). Analytical methods for these algae are described for membrane lipids and neutral lipids including triacylglycerol and wax esters.

Algae are ecologically important organisms and are widely used for basic research, with a focus on for example photosynthesis, evolution, and lipid metabolism. Many biosynthetic pathways of algal lipids have been deciphered using available genomic information. Here we describe methods for lipid analyses from three representative algae, including Archaeplastida, the SAR lineage (Stramenopiles, Alveolata, Rhizaria), and Excavata. Archaeplastida acquired their plastids by primary endosymbiosis, and the others by secondary endosymbiosis with a Rhodophyceae-type plastid in SAR and a Chlorophyceae-type plastid in Excavata (Euglenozoa). Analytical methods for these algae are described for membrane lipids and neutral lipids including triacylglycerol and wax esters.

Cyanobacteria and chloroplasts are believed to share a common ancestor, but synthetic pathways for membrane lipids are different. Lyso-phosphatidic acid (lyso-PA) is the precursor for the synthesis of all membrane lipids and synthesized by an acyl-ACP dependent glycerol-3-phosphate acyltransferase (GPAT) in chloroplasts. In cyanobacteria, GPAT genes are not found and, instead, genes coding for enzymes in the acyl-phosphate dependent lyso-PA synthetic pathway (plsX and plsY) are conserved. We report that the PlsX/Y dependent lyso-PA synthetic pathway is essential in cyanobacteria, but can be replaced by acyl-ACP dependent GPAT from Escherichia coli (plsB) and Arabidopsis thaliana (ATS1). Cyanobacteria thus display the capacity to accept enzymes from other organisms to synthesize essential components. This ability may have enabled them to evolve into current chloroplasts from their ancestral origins.

Heterocysts are the specialized cells for nitrogen fixation in some filamentous cyanobacteria. To protect the oxygen labile nitrogen fixing enzyme, nitrogenase, heterocysts keep their inner environment microoxic by developing layers of barrier on the outside of their outer membranes. Heterocyst specific glycolipids (Hgls) are constituents of the layer of barrier and amphipathic compounds, synthesized from a very long chain fatty alcohol as a hydrophobic tail and a sugar as a polar head. In the model heterocystous cyanobacterium Anabaena sp. PCC 7120, Hgls are made of fatty alcohol with 26 carbons and a glucose, linked by an ether bond in alpha configuration. The fatty alcohol is synthesized via reactions of a polyketide synthase, HglE

Lipid biosynthesis within the chloroplast, or more generally plastids, was conventionally called “prokaryotic pathway,” which produces glycerolipids bearing C18 acids at the sn-1 position and C16 acids at the sn-2 position, as in cyanobacteria such as Anabaena and Synechocystis. This positional specificity is determined during the synthesis of phosphatidate, which is a precursor to diacylglycerol, the acceptor of galactose for the synthesis of galactolipids. The first acylation at sn-1 is catalyzed by glycerol-3-phosphate acyltransferase (GPAT or GPT), whereas the second acylation at sn-2 is performed by lysophosphatidate acyltransferase (LPAAT, AGPAT, or PlsC). Here we present comprehensive phylogenomic analysis of the origins of various acyltransferases involved in the synthesis of phosphatidate, as well as phosphatidate phosphatases in the chloroplasts. The results showed that the enzymes involved in the two steps of acylation in cyanobacteria and chloroplasts are entirely phylogenetically unrelated despite a previous report stating that the chloroplast LPAAT (ATS2) and cyanobacterial PlsC were sister groups. Phosphatidate phosphatases were separated into eukaryotic and prokaryotic clades, and the chloroplast enzymes were not of cyanobacterial origin, in contrast with another previous report. These results indicate that the lipid biosynthetic pathway in the chloroplasts or plastids did not originate from the cyanobacterial endosymbiont and is not “prokaryotic” in the context of endosymbiotic theory of plastid origin. This is another line of evidence for the discontinuity of plastids and cyanobacteria, which has been suggested in the glycolipid biosynthesis.

Erythrobacter flavus strain KJ5 (formerly called Erythrobacter sp. strain KJ5) is a yellowish marine bacterium that was isolated from a hard coral Acropora nasuta in the Karimunjawa Islands, Indonesia. The complete genome sequence of the bacterium has been reported recently. In this study, we examined the carotenoid composition of this bacterium using high-performance liquid chromatography coupled with ESI-MS/MS. We found that the bacterium produced sulfur-containing carotenoids, i.e., caloxanthin sulfate and nostoxanthin sulfate, as the most abundant carotenoids. A new carotenoid zeaxanthin sulfate was detected based on its ESI-MS/MS spectrum. The unique presence of sulfated carotenoids found among the currently known species of the Erythrobacter genus were discussed.

Erythrobacter flavus strain KJ5 (formerly called Erythrobacter sp. strain KJ5) is a yellowish marine bacterium that was isolated from a hard coral in the Karimunjawa Islands of Indonesia., Erythrobacter flavus strain KJ5 (formerly called Erythrobacter sp. strain KJ5) is a yellowish marine bacterium that was isolated from a hard coral in the Karimunjawa Islands of Indonesia. Here, we report the complete genome sequence of the bacterium and provide a useful resource for studies of the biosynthetic pathways of its unique carotenoids.

Microalgal lipids and fatty acids are important components for achieving biofuel because of their potential high productivity. Although fatty acids that have a hydroxy group adjacent to the end of the acyl chain might be an important chemical feedstock, most algae do not accumulate it. To produce (ω−1)-hydroxy fatty acids from 3-hydroxybutylyl-CoA, an intermediate for polyhydroxybutylate biosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, we expressed a gene for the promiscuous 3-ketoacyl-ACP synthase III from Alicyclobacillus acidocalderius (aaKASIII) by the cpc560 promoter. To supply 3-hydroxybutyryl-CoAs for aaKASIII, the phaC gene for polyhydroxybutylate polymerase was deleted, and the phaAB genes for 3-hydroxybutyryl-CoA synthesis from Cupriavidus necator were overexpressed. The genetically modified strain synthesized 15-hydroxyhexadecanoic acid, 17-hydroxyoctadecanoic acid, and 17-hydroxyoctadec-9-enoic acid, and accumulated approximately 2.1 mol% of (ω−1)-hydroxy fatty acids in total fatty acids under illumination with 70 μmol photons m−2 s−1, although its growth was severely retarded. Under weak light (35 μmol photons m−2 s−1) conditions, the strain grew as well as the wild-type and showed lower hydroxy fatty acids (0.04 mol%) accumulation than that at higher illumination levels. The photosynthetic activity of this strain was lower than that of wild-type cells, suggesting that high light conditions enhanced hydroxy fatty acids production and inhibited photosynthesis. (ω−1)-Hydroxy fatty acids were not predominantly observed in the galactolipids from thin-layer chromatography, which are the major lipid classes in cyanobacteria. To the best of our knowledge, this is the first report on photoautotrophic production of fatty acids possessing a functional group near the end of the acyl chain in cyanobacteria.

Glycolipids constitute the majority of membrane components in oxygenic photosynthetic organisms, whereas they are minor lipids in other organisms. In cyanobacteria, three glycolipids comprise ~90 mol% of the total lipids in thylakoid membranes, where photosynthetic electron transport occurs. Among these glycolipids, 80 mol% are galactolipids (monogalactosyldiacylglycerol and digalactosyldiacylglycerol). Galactolipids are well conserved in oxygenic photosynthetic organisms and are believed to be essential for the integrity of the membrane system. It remains unclear, however, which part(s) of the galactolipid structure is the key factor for their function, e.g., the sugar moiety and/or the anomeric configuration. To address this issue, several bacterial membrane glycolipid synthase genes have been introduced into cyanobacteria to test for complementation of knocked-out genes involved in galactolipid biosynthesis. In this review, we summarize recent advances in the analyses of sugar species and configurations of glycolipids heterologously synthesized in the thylakoid membrane and discuss their functional importance.

The first ever cyanobacterial genome sequence was determined two decades ago and CyanoBase (http://genome.microbedb.jp/cyanobase), the first database for cyanobacteria was simultaneously developed to allow this genomic information to be used more efficiently. Since then, CyanoBase has constantly been extended and has received several updates. Here, we describe a new large-scale update of the database, which coincides with its 20th anniversary. We have expanded the number of cyanobacterial genomic sequences from 39 to 376 species, which consists of 86 complete and 290 draft genomes. We have also optimized the user interface for large genomic data to include the use of semantic web technologies and JBrowse and have extended community-based reannotation resources through the re-annotation of Synechocystis sp. PCC 6803 by the cyanobacterial research community. These updates have markedly improved CyanoBase, providing cyanobacterial genome annotations as references for cyanobacterial research.

Digalactosyldiacylglycerol (DGDG) is a major component of thylakoid membranes, occupying approximately 20% of the membrane system. This lipid composition is conserved from cyanobacteria to the chloroplasts of terrestrial plants, suggesting that DGDG is important for the function of photosynthetic membranes. Here we isolated the gene for DGDG synthase in the cyanobacterium Synechococcus elongatus PCC 7942 (7942dgdA) and found that this gene is essential for this species. 7942dgdA could be knocked out only when genes for cyanobacterial or plant DGDG synthases were expressed, indicating that the important factor was not the specific synthetic pathway but the lipid product. Lack of DGDG could not be compensated by the other membrane lipids in S. elongatus PCC 7942 or by glucosylgalactosyldiacylglycerol synthesized by the β-GlcT gene of Chloroflexus aurantiacus. These results reveal that DGDG has an indispensable role in S. elongatus PCC 7942 and that the second galactose molecule is key. Conservation and distribution of the galactolipid synthetic pathway among oxygenic phototrophs is discussed. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Background Exposure of the American bullfrog Lithobates catesbeianus tadpoles to low temperature affects many biological processes including lipid metabolism and the thyroid hormone (TH) signaling pathway, resulting in arrest of TH-induced metamorphosis. To clarify what molecular events occur in this phenomenon, we investigated the glycerophospholipid and fatty acid (FA) compositions, the activities of mitochondrial enzymes and the transcript levels of related genes in the liver of control (26 °C) and cold-treated (4 °C) tadpoles with or without 5 nM 3,3′,5-triiodothyronine (T3). Results Exposure to T3 decreased the tail height and polyunsaturation of FAs in the glycerophospholipids, and increased plasma glucose levels and transcript levels of primary TH-response genes including TH receptor, and some energy metabolic (cox4, srebp1 and fas) and FA chain elongase genes (elovl3 and elovl5). However, these T3-induced responses were abolished at 4 °C. Exposure to cold temperature enhanced plasma glucose, triglyceride and free FA levels, monounsaturation of FAs, mitochondrial enzymes activities (cytochrome c oxidase and carnitine palmitoyltransferase; U/g liver), with the upregulation of the genes involved in glycogenolysis (pygl), gluconeogenesis (pck1 and g6pc2), FA β-oxidation (acadl), and cholesterol uptake and synthesis (hmgcr, srebp2 and ldlr1), glycerophospholipids synthesis (pcyt1, pcyt2, pemt, and pparg), and FA monounsaturation (scd1) and chain elongation (elovl1 and elovl2). T3 had little effect on the cold-induced changes. Conclusions Our study demonstrated that exposures to T3 and cold temperature exert different effects on lipid metabolism, resulting in changes in the FA composition in glycerophospholipids, and suggests that a cold-induced signal may block TH-signaling pathway around primary TH-response genes. Electronic supplementary material The online version of this article (doi:10.1186/s13578-016-0087-5) contains supplementary material, which is available to authorized users.

Cyanobacteria carry out oxygenic photosynthesis and share many features with chloroplasts, including thylakoid membranes, which are mainly composed of membrane lipids and protein complexes that mediate photosynthetic electron transport. Although the functions of the various thylakoid protein complexes have been well characterized, the details underlying the biogenesis of thylakoid membranes remain unclear. Galactolipids are the major constituents of the thylakoid membrane system, and all the genes involved in galactolipid biosynthesis were recently identified. In this chapter, I summarize recent advances in our understanding of the factors involved in thylakoid development, including regulatory proteins and enzymes that mediate lipid biosynthesis.