Award: OCE-1343773

Intelectual Merit Diverse heterotrophic bacteria drive biogeochemical cycling in the ocean. The most abundant types of marine bacteria are oligotrophs with small, streamlined genomes. The metabolic controls that regulate the response of abundant oligotrophic bacteria to environmental conditions remain unclear. Our work revealed that low transcriptional control is one feature of a successful adaptive strategy of marine oligotrophic bacteria. Although responses of bacteria to environmental conditions are commonly regulated at the level of transcription, gene expression in the most abundant bacteria in the ocean appears to be regulated by mechanisms other than transcriptional control. This work obtained an unexpected result that advaced knowledge of the ecology of bacteria in the ocean. Bacteria respond to environmental stimuli using transcriptional control, but this does not appear to be the case for marine bacteria such as Candidatus Pelagibacter ubique, a cultivated representative of the SAR11 clade, the most abundant organism in the ocean. This bacterium has a small, streamlined genome and other genetic characteristics suggesting that transcriptional control is low in Pelagibacter and limits its response to environmental conditions. This research examined strains of bacteria that are closely related to the most abundant types of bacteria in the ocean. The results revealed that only 0.1% of protein-encoding genes appear to be under transcriptional control in Pelagibacter and in another oligotroph (SAR92) whereas >10% of genes were under transcriptional control in the copiotrophs Polaribacter MED152 and Ruegeria pomeroyi. The essence of the experimental results can be summed up as follows. When growth changed transcript levels remained steady in Pelagibacter and SAR92 but shifted in MED152 and Ruegeria. These observations suggest that low transcriptional control contributes to the adaptive strategy of Pelagibacter and possibly other oligotrophic microbes, which dominate microbial communities in the oceans. Broader Impacts This project supported a research scientist and provided samples and data for a M.S. student who successfully defended their M.S. thesis and published the outcomes of their work in a peer reviewed publication in 2016. Last Modified: 05/07/2017 Submitted by: Matthew T Cottrell