Cyanobacterial pigments have attracted considerable attention in industry due to their bioactive potential and natural origin. In the present study, the growth dynamics and pigment composition, in terms of chlorophyll a, total carotenoids and phycobiliprotein content, of four cyanobacterial strains isolated from thermal springs, namely Oscillatoria subbrevis CZS 2201, Phormidium ambiguum CZS 2205, Nostoc calcicola TSZ 2203, and Synechococcus sp. CZS 2204, were investigated. The analysis revealed that the maximum quantity of chlorophyll a and total carotenoids was observed in Oscillatoria subbrevis CZS 2201 (26.49 and 3.44 µg mL-1), followed by Phormidium ambiguum CZS 2205 (18.64 and 2.32 µg mL-1), whereas a minimum amount was detected in Synechococcus sp. CZS 2204 (12.13 and 1.24 µg mL-1), respectively. In addition, Oscillatoria subbrevis CZS 2201 showed higher quantity of phycobiliproteins, especially C-phycocyanin (45.81 mg g-1), C-phycoerythrin (64.17 mg g-1) and C-allophycocyanin (27.45 mg g-1). Moreover, carotenoid derivatives of Oscillatoria subbrevis CZS 2201 were also identified, among which β-carotene was the dominant form (1.94 µg mL-1), while the accumulation of zeaxanthin and myxoxanthophyll was relatively high (0.53 and 0.41 µg mL-1, respectively) compared with echinenone and cryptoxanthin (0.34 and 0.23 µg mL-1, respectively). The study revealed that Oscillatoria subbrevis CZS 2201 was a potent producer of secondary carotenoids, including myxoxanthophyll.

• Keywords
• biological activities, carotenoids, chromatography, cyanobacteria, extraction of pigments, identification, myxoxanthophyll,
• Publication type
• Journal Article MeSH

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality remains underexplored. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes that fine-tune light capture, such as state transitions, or the efficiency of energy transfer from phycobilisomes to photosystems (PS). We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the plastoquinone (PQ) pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

• Keywords
• Cyanobacteria, Light harvesting, Light quality, Photomorphogenesis, Photosynthesis, State transitions,
• MeSH
• Acclimatization * MeSH
• Photosynthesis * physiology   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Light * MeSH
• Synechocystis * physiology   radiation effects   metabolism   growth & development   MeSH
• Electron Transport MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH

Photosynthetic organisms harvest light using pigment-protein complexes. In cyanobacteria, these are water-soluble antennae known as phycobilisomes (PBSs). The light absorbed by PBS is transferred to the photosystems in the thylakoid membrane to drive photosynthesis. The energy transfer between these complexes implies that protein-protein interactions allow the association of PBS with the photosystems. However, the specific proteins involved in the interaction of PBS with the photosystems are not fully characterized. Here, we show in Synechocystis sp. PCC 6803 that the recently discovered PBS linker protein ApcG (sll1873) interacts specifically with PSII through its N-terminal region. Growth of cyanobacteria is impaired in apcG deletion strains under light-limiting conditions. Furthermore, complementation of these strains using a phospho-mimicking version of ApcG causes reduced growth under normal growth conditions. Interestingly, the interaction of ApcG with PSII is affected when a phospho-mimicking version of ApcG is used, targeting the positively charged residues interacting with the thylakoid membrane, suggesting a regulatory role mediated by phosphorylation of ApcG. Low-temperature fluorescence measurements showed decreased PSI fluorescence in apcG deletion and complementation strains. The PSI fluorescence was the lowest in the phospho-mimicking complementation strain, while the pull-down experiment showed no interaction of ApcG with PSI under any tested condition. Our results highlight the importance of ApcG for selectively directing energy harvested by the PBS and imply that the phosphorylation status of ApcG plays a role in regulating energy transfer from PSII to PSI.

• MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Phycobilisomes metabolism   MeSH
• Energy Transfer physiology   MeSH
• Synechocystis * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Phycobilisomes MeSH

Unicellular nitrogen fixing cyanobacteria (UCYN) are abundant members of phytoplankton communities in a wide range of marine environments, including those with rapidly changing nitrogen (N) concentrations. We hypothesized that differences in N availability (N2 vs. combined N) would cause UCYN to shift strategies of intracellular N and C allocation. We used transmission electron microscopy and nanoscale secondary ion mass spectrometry imaging to track assimilation and intracellular allocation of 13C-labeled CO2 and 15N-labeled N2 or NO3 at different periods across a diel cycle in Cyanothece sp. ATCC 51142. We present new ideas on interpreting these imaging data, including the influences of pre-incubation cellular C and N contents and turnover rates of inclusion bodies. Within cultures growing diazotrophically, distinct subpopulations were detected that fixed N2 at night or in the morning. Additional significant within-population heterogeneity was likely caused by differences in the relative amounts of N assimilated into cyanophycin from sources external and internal to the cells. Whether growing on N2 or NO3, cells prioritized cyanophycin synthesis when N assimilation rates were highest. N assimilation in cells growing on NO3 switched from cyanophycin synthesis to protein synthesis, suggesting that once a cyanophycin quota is met, it is bypassed in favor of protein synthesis. Growth on NO3 also revealed that at night, there is a very low level of CO2 assimilation into polysaccharides simultaneous with their catabolism for protein synthesis. This study revealed multiple, detailed mechanisms underlying C and N management in Cyanothece that facilitate its success in dynamic aquatic environments.

• Keywords
• Crocosphaera subtropica (former Cyanothece sp. ATCC 51142), Cyanothece, TEM, carbon fixation, nanoSIMS, nitrogen fixation, photosynthesis,
• Publication type
• Journal Article MeSH

Phototrophic microorganisms are promising resources for green biotechnology. Compared to heterotrophic microorganisms, however, the cellular economy of phototrophic growth is still insufficiently understood. We provide a quantitative analysis of light-limited, light-saturated, and light-inhibited growth of the cyanobacterium Synechocystis sp. PCC 6803 using a reproducible cultivation setup. We report key physiological parameters, including growth rate, cell size, and photosynthetic activity over a wide range of light intensities. Intracellular proteins were quantified to monitor proteome allocation as a function of growth rate. Among other physiological acclimations, we identify an upregulation of the translational machinery and downregulation of light harvesting components with increasing light intensity and growth rate. The resulting growth laws are discussed in the context of a coarse-grained model of phototrophic growth and available data obtained by a comprehensive literature search. Our insights into quantitative aspects of cyanobacterial acclimations to different growth rates have implications to understand and optimize photosynthetic productivity.

• Keywords
• computational biology, growth model, infectious disease, light limitation, microbiology, photoinhibition, phototrophic growth laws, proteome allocation, resource allocation, systems biology,
• MeSH
• Biotechnology MeSH
• Photosynthesis genetics   MeSH
• Phototrophic Processes genetics   MeSH
• Proteome genetics   MeSH
• Cyanobacteria genetics   growth & development   metabolism   MeSH
• Light MeSH
• Synechocystis genetics   growth & development   MeSH
• Cell Size MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Proteome MeSH