Changes in the Vibrio harveyi Cell Envelope Subproteome During Permanence in Cold Seawater

Previous work demonstrated that physiological, morphological, and gene expression changes as well as the time-dependent entry into the viable but not culturable (VBNC) state are used by Vibrio species to survive and cope with diverse stress conditions including seasonal temperature downshifts and starvation. To learn more about the nature and specific contribution of membrane proteins to cell adaptation and survival, we analyzed variations in the protein composition of cell envelope and related them to morphological and physiological changes that were taking place during the long-term permanence of Vibrio harveyi in seawater microcosm at 4 °C. We found that after 21 days of permanence, nearly all population (ca. 99 %) of V. harveyi acquired the VBNC phenotype. Although the size of V. harveyi cells gradually decreased during the incubation time, we found that this morphological change was not directly related to their entry into the VBNC state. Our proteomic study revealed that the level of membrane proteins playing key roles in cellular transport, maintenance of cell structure, and in bioenergetics processes remained unchanged along starvation at low temperature, thus suggesting that V. harveyi might need these proteins for the long-term survival and/or for the resuscitation process. On a contrary, the level of two proteins, elongation factor Tu (EF-TU) and bacterioferritin, greatly increased reaching the maximal values by the end of the incubation period. We further discuss the above data with respect to the putative roles likely exerted by membrane proteins during transition to and maintaining of the VBNC state.