Journal
FRONTIERS IN MICROBIOLOGY
Volume 12, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fmicb.2021.620915
Keywords
Crocosphaera subtropica (former Cyanothece sp; ATCC 51142); Cyanothece; photosynthesis; carbon fixation; nitrogen fixation; nanoSIMS; TEM
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Funding
- Netherlands Organization for Scientific Research (NWO) [175.010.2009.011]
- Czech Ministry of Education, Youth and Sport through the BioImaging Research Infrastructure project [LM2015062]
- Hungarian Academic Foundation (OTKA) [K128950]
- Ministry of Education, Youth and Sports of the Czech Republic (OP RDE) [CZ.02.1.01/0.0/0.0/16-026/0008413]
- Czech Science Foundation (GA CR) [18-24397S]
- LEFE-INSU funding program
- Czech Science Foundation [GACR 20-17627S, 20-02827Y]
- ILES (Illuminating Lake Ecosystem) project through the Leibniz Competition [SAW-2015-IGB-1]
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Unicellular nitrogen fixing cyanobacteria (UCYN) are abundant in marine phytoplankton communities and can shift their strategies of intracellular N and C allocation under different N availabilities. This study revealed detailed mechanisms in Cyanothece for C and N management, including subpopulations fixing nitrogen at different times and the impact of external and internal nitrogen assimilation sources on cyanophycin synthesis. The prioritization of cyanophycin synthesis when N assimilation rates are highest was observed, along with the bypassing of cyanophycin synthesis in favor of protein synthesis once a cyanophycin quota is met.
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 (N-2 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 C-13-labeled CO2 and N-15-labeled N-2 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 N-2 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 N-2 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.
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