Crocosphaera and Cyanothece are both unicellular, nitrogen-fixing cyanobacteria that prefer different environments. Whereas Crocosphaera mainly lives in nutrient-deplete, open oceans, Cyanothece is more common in coastal, nutrient-rich regions. Despite their physiological similarities, the factors separating their niches remain elusive. Here we performed physiological experiments on clone cultures and expand upon a simple ecological model to show that their different niches can be sufficiently explained by the observed differences in their photosynthetic capacities and rates of carbon (C) consumption. Our experiments revealed that Cyanothece has overall higher photosynthesis and respiration rates than Crocosphaera. A simple growth model of these microorganisms suggests that C storage and consumption are previously under-appreciated factors when evaluating the occupation of niches by different marine nitrogen fixers.

Balaton Limnological Research Institute Eötvös Loránd Research Network Tihany Hungary

Cellular Imaging Laboratory Biological Research Center Eötvös Loránd Research Network Szeged Hungary

Graduate School of Oceanography University of Rhode Island Narragansett RI 02882 USA

Institute of Microbiology The Czech Academy of Sciences Opatovický mlýn 37901 Třeboň Czech Republic

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The biogenesis and maintenance of PSII: Recent advances and current challenges