Lawrence Berkeley National Laboratory

The mechanisms of Desulfovibrio vulgaris Hildenborough responses to long-term NaCl exposure were studied by global transcriptional and metabolite analyses. The growth of D. vulgaris was inhibited by high salinity, and salt inhibition could be relieved by an addition of amino acids (e.g., glutamate, alanine) or yeast extract. Salt shock (sudden increase in salt concentration) and salt adaptation (inoculating cells in the medium containing high concentrations of salt) showed a significant difference in respective transcriptomes. Salt adaptation induced expression of genes involved in amino acid biosynthesis and transportation, electron transfer, hydrogen oxidation, and general stress responses (e.g., heat shock proteins, phage shock proteins, and oxidative stress response proteins). Genes involved in energy metabolism, cell motility, and phage structures were repressed. Genes involved in Na+/H+ transport, K+ uptake and transportation, and proline biosynthesis and transportation were not significantly affected. Metabolite assays and external addition of amino acids into the growth medium of D. vulgaris suggest that amino acids, such as glutamate and alanine may accumulate as osmoprotectants in D. vulgaris. A conceptual model is proposed to link our observed results to currently available knowledge for further understanding the mechanisms of adaptation of D. vulgaris to sodium chloride.