A copper-transporting P-type ATPase found in the thylakoid membrane of the cyanobacterium Synechococcus species PCC7942

P-type ATPases constitute a large family of cation pumps that play crucial physiological roles in many organisms, including bacteria, plants and mammals. They are postulated to play important roles in a variety of environmental adaptation systems. Recently, we cloned two distinct putative P-type ATPase genes (pacS and pacL) from a photosynthetic cyanobacterium, Synechococcus species PCC7942. in this study, one of the gene products (named PacS) was found to possess a putative metal-binding motif (Gly-Met-X-Cys-X-X-Cys) in its N-terminal portion. Thus we supposed that this ATPase may function as a metal pump. Indeed, the results of Northern blotting analysis showed that pacS-mRNA specifically increases upon addition of copper or silver to the growth medium. The results of Western blotting analysis confirmed the view that PacS accumulates in copper-treated Synechococcus cells. Thus we concluded that the expression of PacS ATPase is regulated in response to the change in concentration of external metals, namely copper and silver. Consistent with this, an insertional inactivation mutant of pacS exhibited hypersensitivity in terms of growth to these potentially toxic metals, it was also revealed that PacS was mainly located in the thylakoid membrane, in which the photosynthetic reactions take place. This P-type ATPase in the thylakoid membrane is implicated as a copper-transporting system that may be involved in copper-homeostasis crucial to the photosynthetic thylakoid function.     

Functional phycobilisome core structures in a phycocyanin-less mutant of cyanobacterium Synechococcus sp. PCC 7942

We have constructed a mutant Synechococcus sp. PCC 7942, termed R2HECAT, in which the entire phycobilisome rod operon has been deleted. In the whole cell absorption spectra of R2HECAT, the peak corresponding to phycocyanin (PC), max620 nm, could not be detected. However, a single pigment-protein fraction with max=654 nm could be isolated on sucrose gradients from R2HECAT. Analysis of this pigment-protein fraction by non-denaturing PAGE indicates an apparent molecular mass of about 1200–1300 kDa. On exposure to low temperature, the isolated pigment-protein complex dissociated to a protein complex with a molecular mass of about 560 kDa. When analysed by SDS-PAGE, the pigment-protein fraction was found to consist of the core polypeptides but lacked PC, 27, 33, 30, and the 9 kDa polypeptides which are a part of the rods. All the chromophore bearing polypeptides of the core were found to be chromophorylated. CD as well as absorption spectra showed the expected maxima around 652 and 675 nm from allophycocyanin (APC) and allophycocyanin B (APC-B) chromophores. Low temperature fluorescence and excitation spectra also showed that the core particles were fully functional with respect to the energy transfer between the APC chromophores. We conclude that PC and therefore the rods are dispensable for the survival of Synechococcus sp. PCC 7942. The results indicate that stable and functional core can assemble in absence of the rods. These rod-less phycobilisome core is able to transfer energy to Photosystem II.Abbreviations PS II Photosystem II - PC phycocyanin - APC allophycocyanin - APC-B allophycocyanin B - PAGE polyacrylamide gel electrophoresis - Cml chloramphenicol - kbp kilobase pairs     

Dynamic responses of photosystem II and phycobilisomes to changing light in the cyanobacterium Synechococcus sp. PCC 7942

We have examined the molecular and photosynthetic responses of a planktonic cyanobacterium to shifts in light intensity over periods up to one generation (7 h). Synechococcus sp. PCC 7942 possesses two functionally distinct forms of the D1 protein, D1∶1 and D1∶2. Photosystem II (PSII) centers containing D1∶1 are less efficient and more susceptible to photoinhibition than are centers containing D 1∶2. Under 50 μmol photons· m^?2·s^?1, PSII centers contain D1∶1, but upon shifts to higher light (200 to 1000 μmol photons·m^?2·s^?1), D1∶1 is rapidly replaced by D 1∶2, with the rate of interchange dependent on the magnitude of the light shift. This interchange is readily reversed when cells are returned to 50 μmol photons·m^?2·s^?1. If, however, incubation under 200 μmol photons·m^?2·s^?1 is extended, D1∶1 content recovers and by 3 h after the light shift D1∶1 once again predominates. Oxygen evolution and chlorophyll (Chl) fluorescence measurements spanning the light shift and D1 interchanges showed an initial inhibition of photosynthesis at 200 μmol photons·m^?2·s^?1, which correlates with a proportional loss of total D1 protein and a cessation of growth. This was followed by recovery in photosynthesis and growth as the maximum level of D 1∶2 is reached after 2 h at 200 μmol photons·m^?2·s^?1. Thereafter, photosynthesis steadily declines with the loss of D1∶2 and the return of the less-efficient D1∶1. During the D1∶1/D1∶2 interchanges, no significant change occurs in the level of phycocyanin (PC) and Chl a, nor of the phycobilisome rod linkers. Nevertheless, the initial PC/Chl a ratio strongly influences the magnitude of photo inhibition and recovery during the light shifts. In Synechococcus sp. PCC 7942, the PC/Chl a ratio responds only slowly to light intensity or quality, while the rapid but transient interchange between D1∶1 and D 1∶2 modulates PSII activity to limit damage upon exposure to excess light.     

Cloning of the phycobilisome rod linker genes from the cyanobacterium Synechococcus sp. PCC 6301 and their inactivation in Synechococcus sp. PCC 7942

Coexpression of pairs of nonhaemolytic H1yA mutants in the recombination-deficient (recA) strain Escherichia coli HB101 resulted in a partial reconstitution of haemolytic activity, indicating that the mutation in one H1yA molecule can be complemented by the corresponding wild-type sequence in the other mutant HlyA molecule and vice versa. This suggests that two or more HlyA molecules aggregate prior to pore formation. Partial reconstitution of the haemolytic activity was obtained by the combined expression of a nonhaemolytic HlyA derivative containing a deletion of five repeat units in the repeat domain and several nonhaemolytic HlyA mutants affected in the pore-forming hydrophobic region. The simultaneous expression of two inactive mutant HlyA proteins affected in the region at which HlyA is covalently modified by HlyC and the repeat domain, respectively, resulted in a haemolytic phenotype on blood agar plates comparable to that of wild-type haemolysin. However, complementation was not possible between pairs of HlyA molecules containing site-directed mutations in the hydrophobic region and the modification region, respectively. In addition, no complementation was observed between HlyA mutants with specific mutations at different sites of the same functional domain, i.e. within the hydrophobic region, the modification region or the repeat domain. The aggregation of the HlyA molecules appears to take place after secretion, since no extracellular haemolytic activity was detected when a truncated but active HlyA lacking the C-terminal secretion sequence was expressed together with a non-haemolytic but transport-competent HlyA mutant containing a deletion in the repeat domain.     

Factors influencing the phycobilisome rod composition of the cyanobacterium Synechococcus sp. PCC 7942: Effects of reduced phycocyanin content, lack of rod-linkers, and over-expression of the rod-terminating linker

Four novel mutants with altered phycobilisomes were constructed in the cyanobacterium Synechococcus 7942 to study factors influencing the rod length and composition. These mutants show (1) reduced phycocyanin content, (2) reduced phycocyanin content combined with loss of the 33 kDa linker, (3) loss of the 30 kDa rod-linker and (4) overexpression of the 9 kDa rod terminating linker. For these mutants we determined the 33 to 27 kDa and 30 to 27 kDa linker ratios in the isolated phycobilisomes and compared these ratios with those in the wild type. The 30 kDa linker can be incorporated into the rods in absence of the 33 kDa linker. The incorporation of the 30 kDa linker is lower in absence of the 33 kDa linker. When the 30 kDa linker is missing, an increase in the level of the 33 kDa linker is seen, indicating that there could be an excess of the 33 kDa linker in the cells. Our results also show that a reduction in the phycocyanin content causes a decrease in the rod length simultaneously with a reduction of the 30/27 linker ratio, without altering the 33/27 ratio. Reduced phycocyanin content and absence of the 33 kDa linker cause a dramatic reduction in the incorporation of the 30 kDa linker into the rods in the mutant B2SMIKM. Over-expression of the 9 kDa linker results in a decreased incorporation of both the 33 and 30 kDa linkers into the rods, the effect being more pronounced for the 30 kDa linker. This result indicates that the level of the 9 kDa linker relative to those of the 33 and the 30 kDa linkers may be an important determinant of the phycobilisome rod length.     

HtpG,the prokaryotic homologue of Hsp90, stabilizes a phycobilisome protein in the cyanobacterium Synechococcus elongatus PCC 7942

HtpG, a homologue of HSP90, is essential for thermotolerance in cyanobacteria. It is not known how it plays this important role. We obtained evidence that HtpG interacts with linker polypeptides of phycobilisome in the cyanobacterium Synechococcus elongatus PCC 7942. In an htpG mutant, the 30 kDa rod linker polypeptide was reduced. In vitro studies with purified HtpG and phycobilisome showed that HtpG interacts with the linker polypeptide as well as other linker polypeptides to suppress their thermal aggregation with a stoichiometry of one linker polypeptide/HtpG dimer. We constructed various domain‐truncated derivatives of HtpG to identify putative chaperone sites at which HtpG binds linker polypeptides. The middle domain and the N‐terminal domain, although less efficiently, prevented the aggregation of denatured polypeptides, while the C‐terminal domain did not. Truncation of the C‐terminal domain that is involved in the dimerization of HtpG led to decrease in the anti‐aggregation activity, while fusion of the N‐terminal domain to the middle domain lowered the activity. In vitro studies with HtpG and the isolated 30 kDa rod linker polypeptide provided basically similar results to those with HtpG and phycobilisome. ADP inhibited the anti‐aggregation activity, indicating that a compact ADP conformational state provides weaker aggregation protection compared with the others.     

Interaction of ferredoxin:NADP+ oxidoreductase with phycobilisomes and phycobilisome substructures of the cyanobacterium Synechococcus sp. strain PCC 7002

The enzyme ferredoxin-NADP(+) oxidoreductase (FNR) from Synechococcus sp. PCC 7002 has an extended structure comprising three domains (FNR-3D) (Schluchter, W. M., and Bryant, D. A. (1992) Biochemistry 31, 3092-3102). Phycobilisome (PBS) preparations from wild-type cells contained from 1.0 to 1.6 molecules of FNR-3D per PBS, with an average value of 1.3 FNR per PBS. A maximum of two FNR-3D molecules could be specifically bound to wild-type PBS via the N-terminal, CpcD-like domain of the enzyme when exogenous recombinant FNR-3D (rFNR-3D) was added. To localize the enzyme within the PBS, the interaction of PBS and their substructures with rFNR-3D was further investigated. The binding affinity of rFNR-3D for phycocyanin (PC) hexamers, which contained a 22-kDa proteolytic fragment derived from CpcG, the L(RC)(27) linker polypeptide, was higher than its affinity for PC hexamers containing no linker protein. PBS from a cpcD3 mutant, which lacks the 9-kDa, PC-associated rod linker, incorporated up to six rFNR-3D molecules per PBS. PBS of a cpcC mutant, which has peripheral rods that contain single PC hexamers, also incorporated up to six rFNR-3D molecules per PBS. Direct competition binding experiments showed that PBS from the cpcD3 mutant bound more enzyme than PBS from the cpcC mutant. These observations support the hypothesis that the enzyme binds preferentially to the distal ends of the peripheral rods of the PBS. These data also show that the relative affinity order of the PC complexes for FNR-3D is as follows: (alpha(PC)beta(PC))(6)-L(R)(33) > (alpha(PC)beta(PC))(6)-L(RC)(27) > (alpha(PC)beta(PC))(6). The data suggest that, during the assembly of the PBS, FNR-3D could be displaced to the periphery according to its relative binding affinity for different PC subcomplexes. Thus, FNR-3D would not interfere with the light absorption and energy transfer properties of PC in the peripheral rods of the PBS. The implications of this localization of FNR within the PBS with respect to its function in cyanobacteria are discussed.     

Ultrastructure of cell wall and thylakoid membranes of the thermophilic cyanobacterium Synechococcus lividus under the influence of temperature shifts

The ultrastructure of the cell wall and the thylakoid membranes of the thermophilic cyanobacterium Synechococcus lividus was studied by freezefracture electron microscopy after temperature shifts. Different fracture faces of the outer, the cytoplasmic and the thylakoid membranes were demonstrated when the preparation-temperature was in the range of the optimal growth temperature at 52°C or after fixation at 52°C. In the outer membrane of the cell wall two fracture faces with holes and 7.5 nm intramembrane particles were detected. On both the outer (EF) and inner (PF) leaflet of the cytoplasmic membrane randomly distributed particles were demonstrated. The particle density on the PF-face was approx. three times that of the EF-face. The EF-face of the thylakoid membrane exposed rows of particles with an average diameter of 10 nm. The spacing between the particle rows was 35–50 nm. This regular particle arrangement on the EF-face was demonstrated only in a few cases. Mostly the intramembrane particles were distributed randomly on the thylakoid fracture faces. The particle density of thylakoids with a random distribution was approx. in the same range both on the EF-and PF-face. The EF-particles fall into four groups of 9,10,11, and 12.5 nm. The main particle class was the 10 nm class. The PF-face exposed smaller particles with two maxima at 8.5–9 nm and 10 nm. When Synechococcus lividus OH-53s was chilled to temperatures below 30–35°C before the freeze-etch preparation a phase transition took place after the temperature shift. On the fracture faces of the thylakoid and cytoplasmic membranes particle depleted areas occurred. The size of the areas were different in both membranes and dependent on the velocity of cooling. Contrary to Synechococcus lividus OH-53s in the mesophilic Synechococcus strain 6910 the phase transition point was 15°C. The lower phase transition point may be due to a higher content of unsaturated fatty acids.Dedicated to Prof. D. Peters (Hamburg) on the occasion of the 65th anniversary of his birthday     

Involvement of DnaK3, one of the three DnaK proteins of cyanobacterium Synechococcus sp. PCC7942, in translational process on the surface of the thylakoid membrane

The Synechococcus sp. PCC7942 strain carrying a missense mutation in the peptide-binding domain of DnaK3, one of the essential dnaK gene products, revealed temperature-sensitive growth. We also isolated suppressor mutants of this strain. One of the suppressors was mapped in the ribosomal protein gene rpl24 (syc1876), which encodes the 50S ribosomal protein L24. Subcellular localization of three DnaK proteins was determined, and the results indicated that a quantity of DnaK3 was dislocated from membrane-bound polysomes when dnaK3 temperature-sensitive mutant was incubated at non-permissive temperatures. Furthermore, we examined the photosystem II reaction center protein D1 and detected a translational intermediate polypeptide in membrane-bound polysome fractions prepared from dnaK3 temperature-sensitive cells grown at high temperature. These characteristic features of DnaK3 localizations and detection of D1 protein intermediate were not observed in the suppressor mutant even at high temperatures.     

Membrane lipid composition and restoration of photosynthesis during low temperature acclimation in Synechococcus sp. strain PCC 7942

We compared temperature acclimation of the cyanobacterium Synechococcus sp. strain PCC 7942 and two psbA inactivation mutants, R2K1 and R2S2C3, following shifts from 37 to 25°C. Wild-type cultures incubated in the dark at 25°C showed no chill-induction of lipid desaturation, probably because the lipid acclimation is dependent on photosynthesis. Incubation in the light at 25°C, however, induced considerable increases in membrane lipid desaturation, and within 24 h the monoenoic fatty acids increased from about 46 to about 57%. In parallel with this desaturation the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol (MGDG/DGDG) increased. Both of these lipid changes increase the repulsive forces of the hydrophobic chains of the membrane lipids and thereby alter the physical properties of the membrane. As expected, under irradiation this temperature shift also induced a reversible replacement of the constitutive photosystem II protein, D1:1, with an alternative stress form, D1:2. Photosynthesis decreased to 42% of the control level within the initial 2 h of cold incubation, but later recovered. The D1:2 protein accumulated to high levels between 2 and 4 h after the temperature shift, when desaturation of membrane lipids and MGDG/DGDG ratio had not yet increased significantly. Much of this accumulated D1:2 protein was in a higher molecular mass form, termed D1:2^*, which is probably an unprocessed precursor form of the protein. In contrast to the wild-type cells the psbA inactivation mutants, R2K1 and R2S2C3 did not accumulate any precursor form of D1 protein either at the optimal or low growth temperature. The R2S2C3 mutant strain expresses only the constitutive D1:1 protein and suffered severe photoinhibition following the temperature shift. Nevertheless, R2S2C3 eventually recovered some photosynthetic activity, induced lipid desaturation and slowly resumed growth at 25°C, thus demonstrating acclimation to the lower growth temperature. The R2K1 mutant synthesizes only the D1:2 stress form of D1 protein and maintained oxygen evolution at a high level (ca 70% of a control rate) after the low temperature shift. Chill-induced lipid desaturation and increase in MGDG/DGDG ratio did proceed but, for unknown reasons the strain did not resume growth at the lower temperature. The physical properties of the membrane lipids were not the limiting factor for growth resumption. Our results demonstrate that in the wild-type the chill-induced desaturation of membrane lipids follows after the exchange of the two forms of the D1 proteins, but the D1 exchange results in accumulation of unprocessed D1:2^* polypeptides until the lipid composition later acclimates. We also show that the lipid desaturation process in Synechococcus sp. strain PCC 7942 is dependent upon photosynthetic activity.     

Lipid diffusion in the thylakoid membranes of the cyanobacterium Synechococcus sp.: effect of fatty acid desaturation

Thylakoid membranes are crucial to photosynthesis in cyanobacteria and plants. In cyanobacteria, genetic modification of membrane lipid composition strongly influences cold tolerance and susceptibility to photoinhibition. We have used fluorescence recovery after photobleaching to measure the diffusion of a lipid-soluble fluorescent marker in cells of the cyanobacterium Synechococcus sp. PCC 7942. We have compared the wild-type strain with a transformant with an increased level of fatty acid unsaturation. The transformant showed a six-fold increase in the diffusion coefficient for the fluorescent marker at growth temperature. This is the first direct measurement of lipid diffusion in a photosynthetic membrane.     

Nutrient-associated elongation and asymmetric division of the cyanobacterium Synechococcus PCC 7942

While tightly regulated, bacterial cell morphology may change substantially in response to environmental cues. Here we describe such changes in the cyanobacterium Synechococcus sp. strain PCC7942. Once maintained in stationary phase, these rod-shaped organisms stop dividing and elongate up to 50-fold. Increase in cell length of a thymidine-auxotroph strain upon thymidine starvation implies that inhibition of DNA replication underlies cell elongation. Elongation occurs under conditions of limiting phosphorus but sufficient nitrogen levels. Once proliferative conditions are restored, elongated cells divide asymmetrically instead of exhibiting the typical fission characterized by mid-cell constriction. The progeny are of length characteristic of exponentially growing cells and are proficient of further proliferation. We propose that the ability to elongate under conditions of cytokinesis arrest together with the rapid induction of cell division upon nutrient repletion represents a beneficial cellular mechanism operating under specific nutritional conditions.     

Cloning and characterization of the secY gene from the cyanobacterium Synechococcus PCC7942.

The secY gene product is an essential component of the Escherichia coli cytoplasmic membrane, which mediates the protein translocation across the membrane. We found a gene homologous to secY in the genome of the cyanobacterium Synechococcus PCC7942. The deduced amino acid sequence, 439 amino acids long, shows 43% homology with that of the E. coli secY. The hydrophobic profile suggests that the Synechococcus SecY protein is an integral membrane protein containing ten membrane-spanning segments, which are closely related to the E. coli counterpart. The SecY protein may participate in the protein translocation across the cytoplasmic or thylakoid membrane in Synechococcus PCC7942.     

Cell surface composition,released polysaccharides,and ionic strength mediate fast sedimentation in the cyanobacterium Synechococcus elongatus PCC 7942

Cyanobacteria are photosynthetic prokaryotes of high ecological and biotechnological relevance that have been cultivated in laboratories around the world for more than 70 years. Prolonged laboratory culturing has led to multiple microevolutionary events and the appearance of a large number of ‘domesticated’ substrains among model cyanobacteria. Despite its widespread occurrence, strain domestication is still largely ignored. In this work we describe Synechococcus elongatus PCC 7942-KU, a novel domesticated substrain of the model cyanobacterium S. elongatus PCC 7942, which presents a fast-sedimenting phenotype. Under higher ionic strengths the sedimentation rate increased leading to complete sedimentation in just 12 h. Through whole genome sequencing and gene deletion, we demonstrated that the Group 3 alternative sigma factor F plays a key role in cell sedimentation. Further analysis showed that significant changes in cell surface structures and a three-fold increase in released polysaccharides lead to the appearance of a fast-sedimenting phenotype. This work sheds light on the determinants of the planktonic to benthic transitions and provides genetic targets to generate fast-sedimenting strains that could unlock cost-effective cyanobacterial harvesting at scale.     

Effect of iron and other nutrient limitations on the pattern of outer membrane proteins in the cyanobacterium Synechococcus PCC7942

When cells of Synechococcus PCC7942 were subjected to either iron or magnesium limitation, there was an appearance of specific proteins in the outer membrane (isolated as the cell wall fraction). Under iron limitation outer membrane polypeptides of M _r 92000, 48000–50000 and 35000 appeared. Specific iron-limited outer membrane proteins (IRMPs) of M _r 52000 and 36000 were also induced in iron-limited cultures of Synechocystis PCC6308. Under magnesium limitation polypeptides of M _r 80000, 67000, 62000, 50000, 28000 and 25000 appeared in the outer membrane. phosphate limitation caused minor changes in the outer membrane protein pattern, with polypeptides of M _r 32000 and one of over 100000 being induced, whereas calcium limitation had no apparent affect.Abbreviations EDDA ethylenediaminedihydroxyphenyl acetic acid - IRMP iron-regulated outer membrane protein - HEPES N-2-hydroxyethyl-piperazine-N-2-ethane sulphonic acid - SDS-PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - PMSF phenylmethylsulphonyl fluoride     

Molecular characterization and redox regulation of phosphoribulokinase from the cyanobacterium Synechococcus sp. PCC 7942

We isolated and characterized a gene encoding phosphoribulokinase (PRK) from Synechococcus sp. PCC 7942. The isolated sequence consisted of a 999 bp open reading frame encoding 333 amino acid residues of PRK. The PRK contained a pair of cysteinyl residues corresponding to Cys16 and Cys55 of spinach PRK regulated by a ferredoxin-thioredoxin system. However, there were seventeen amino acid residues lacking between the two cysteinyl residues compared with those of the chloroplastic enzyme in higher plants. The recombinant PRK of Synechococcus sp. PCC 7942 accounted for about 6-13% of the total soluble protein in the Escherichia coli. The specific activity of the enzyme was 230 micro mol min(-1) (mg protein)(-1). The enzyme activity was completely inactivated by treatment with 5,5'-dithiobis (2-nitrobenzoic acid) (cysteinyl residue-specific oxidant) or was decreased by treatment with H(2)O(2), but was more tolerant to oxidation than that of chloroplast. The oxidized PRK was fully activated by treatment with excessive dithiothreitol. Furthermore, incubation with 3 mM ATP protected the oxidation of the enzyme by either 5,5'-dithiobis (2-nitrobenzoic acid) or H(2)O(2). These results suggest Synechococcus sp. PCC 7942 PRK can be regulated by reversible oxidation/reduction in vitro, but might be resistant to oxidative inactivation in vivo.     

Adaptation of Synechococcus sp. PCC 7942 to phosphate starvation by glycolipid accumulation and membrane lipid remodeling

Organisms use various adaptive strategies against phosphate stress, including lipid remodeling. Here, the response of major membrane lipids to phosphate stress was analyzed in Synechococcus sp. PCC 7942. Unlike plants and eukaryotic microalgae, no significant increases in neutral lipids were found, whereas glycolipids content increased to as high as 6.13% (of dry cell weight, DCW) and phospholipids decreased to 0.34% (of DCW) after 16 days of cultivation without phosphate. Glycolipids accumulation were mainly attributed to the significant increase of digalactosyldiacylglycerol (DGDG) by 50% and sulfoquinovosyldiaclglycerol (SQDG) by 90%, both of which acted as complementary lipids for phosphatidylglycerol (PG) in the cyanobacterial membrane. Also, a notable increase in content (by 48%) of C18 fatty acids (especially C18:1) was observed in all glycolipids at the expense of C12 and C14 (72%). These changes may contribute to membrane fluidity and photosynthetic activity for basic cell metabolism and phosphate stress adaptation. Lipidomic analyses showed the reduction of PG 18:1/16: 0 (by 52%) with the increase of DGDG 18:1/16:0 (133%) and SQDG 18:1/16:0 (245%), strongly suggesting a direct conversion of PG to DGDG and SQDG. Moreover, the decreasing amount of monogalactosyldiacylglycerol (MGDG) 16:1/16:0 (22%) was consistent with the increase of free fatty acids (125%) on day 2 of phosphate absence, which suggested that MGDG is more likely to provide a pool of fatty acids for de novo synthesis of glycolipids. This study provides valuable insight into cyanobacteria adaptation strategies to phosphate stress by membrane lipid remodeling and unveils the underlying acyl chain fluxes into glycolipids.