Light-stimulated growth of proteorhodopsin-bearing sea-ice psychrophile Psychroflexus torquis is salinity dependent

• DOI: 10.1038/ismej.2013.97
• Publication Date: 2013-06-20T15:12:09Z
• Authors: Shi Feng; Shane M Powell; Richard Wilson; John P Bowman
• Keywords: 0301 basic medicine; Rhodopsin; Salinity; 03 medical and health sciences; Light; Stress, Physiological; Rhodopsins, Microbial; Original Article; Ice Cover; Gene Expression Regulation, Bacterial; Flavobacteriaceae

Abstract Proteorhodopsins (PRs) are commonly found in marine prokaryotes and allow microbes to use light as an energy source. In recent studies, it was reported that PR stimulates growth and survival under nutrient-limited conditions. In this study, we tested the effect of nutrient and salinity stress on the extremely psychrophilic sea-ice bacterial species Psychroflexus torquis, which possesses PR. We demonstrated for the first time that light-stimulated growth occurs under conditions of salinity stress rather than nutrient limitation and that elevated salinity is related to increased growth yields, PR levels and associated proton-pumping activity. PR abundance in P. torquis also is post-transcriptionally regulated by both light and salinity and thus could represent an adaptation to its sea-ice habitat. Our findings extend the existing paradigm that light provides an energy source for marine prokaryotes under stress conditions other than nutrient limitation.