Growth dynamics and transcriptional responses of a Red SeaProchlorococcus strain to varying temperatures

Abstract

Prochlorococcus play a crucial role in the ocean's biogeochemical cycling, but it remains controversial how they will respond to global warming. Here we assessed the response to temperature (22–30°C) of the growth dynamics and gene expression profiles of a Red Sea Prochlorococcus strain (RSP50) in a non‐axenic culture. Both the specific growth rate (0.55–0.80 day−1) and cell size (0.04–0.07 μm3) of Prochlorococcus increased significantly with temperature. The primary production released extracellularly ranged from 20% to 34%, with humic‐like fluorescent compounds increasing up to fivefold as Prochlorococcus reached its maximum abundance. At 30°C, genes involved in carbon fixation such as CsoS2 and CsoS3 and photosynthetic electron transport including PTOX were downregulated, suggesting a cellular homeostasis and energy saving mechanism response. In contrast, PTOX was found upregulated at 22°C and 24°C. Similar results were found for transaldolase, related to carbon metabolism, and citrate synthase, an important enzyme in the TCA cycle. Our data suggest that in spite of the currently warm temperatures of the Red Sea, Prochlorococcus can modulate its gene expression profiles to permit growth at temperatures lower than its optimum temperature (28°C) but is unable to cope with temperatures exceeding 30°C.

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“…The thermophiles, which have reached suitable growth conditions within the given temperature range in this study, their abundance showed a signi cant trend of increasing with temperature. The selective effect caused by rising temperature causes some microbes to be dormant even extinction, such as Prochlorococcus [57], cannot adapt to the high temperature environment, which further led to the decline of the alpha diversity of genes. However, this effect was not observed in the experimental groups.…”