Proteome Expression in a Marine Photoheterotroph under Carbon and Nitrogen Limitation

In the oligotrophic ocean, microbes experience extended periods of nutrient starvation and enter phases of slow growth or dormancy [1] under these unfavorable environmental conditions. Some aquatic microbes have acquired genes that enable light-driven metabolism, thought to supplement heterotrophy during times of nutrient stress. One such form of photoheterotrophy is based on proteorhodopsin (PR), a light activated proton pump that can generate a proton motive force for ATP synthesis, flagellar movement, or nutrient uptake. PR is increasingly recognized as a potentially important contributor to the energy budget of microbial communities due to its prevalence across taxa and environments [2].

Here we explore marine photoheterotrophy by using PR-containing model organism Vibrio campbelli to study the effects of carbon and nitrogen limitation on the proteome’s transition during growth from exponential to stationary phase in both light and dark conditions. The proteome was quantified using in vitro isotopic peptide terminal labeling [3]. Proteome expression patterns were generally similar between C- versus N-rich media during exponential growth phase, but did differ in stationary phase, suggesting some protein expression response given the limiting nutrient. There is little effect of light on the overall proteome. Overall, protein-level PR expression was higher under carbon limitation conditions, but there was no survival or growth advantage conferred by PR.

[1] Lennon, J. T. & Jones, S. E. (2011) Nature Rev. Microbiol. 9, 119–130 [2] Pinhassi, J., et al (2016) Microbiol. Mol. Biol. Rev. 80, 929–954 [3] Waldbauer, J., et. al (2017) Anal. Chem. 89, 11498–11504