Dual roles of glycine betaine, dimethylglycine, and sarcosine as osmoprotectants and nutrient sources for <i>Vibrio natriegens</i>

Bacteria respond to osmotic stress by intracellularly accumulating low molecular weight compounds called compatible solutes, also known as osmolytes. Glycine betaine (<i>N</i>,<i>N</i>,<i>N</i>-trimethylglycine, GB) is a highly effective and widely available osmolyte used by bacteria, algae, and plants for abiotic stress protection. Here, we highlight the dual roles of GB, dimethyl glycine (DMG), and sarcosine for both osmoprotection and a less known role as sole carbon sources. First, we showed that the marine halophile <i>Vibrio natriegens</i> can grow in 1% to 7% NaCl and biosynthesize GB, ectoine, and glutamate and import GB, DMG, and sarcosine in response to osmotic stress. Betaine-carnitine-choline transporters (BCCTs) for the uptake of GB and DMG, but not sarcosine, were identified. Bioinformatics analyses uncovered homologs of GB, DMG, and sarcosine catabolism genes (<i>dgcAB_fixAB, gbcA, gbcB, purU, soxBDAG, glyA, glxA</i>) clustered in the <i>V. natriegens</i> genome, and these genes had a limited distribution among vibrios. We showed that <i>V. natriegens</i> ATCC 14048 grew on GB, DMG, and sarcosine as sole carbon sources, and gbcA and <i>dgcA</i> were required for growth. A contiguous catabolism cluster was present in a subset of <i>Vibrio fluvialis</i> strains, and we demonstrated the growth of <i>V. fluvialis</i> 2013V-1197 in DMG and sarcosine as sole carbon sources. Phylogenetic analysis revealed the catabolism cluster did not share a common ancestor among members of the family <i>Vibrionaceae</i>.IMPORTANCECompatible solutes are frequently the most concentrated organic components in marine organisms, allowing them to adapt to high saline environments as well as affording protection to other abiotic stresses. These organic compounds are significant energy stores that have been overlooked for their potential as abundant nutrient sources for bacteria. Our study characterized glycine betaine (GB), dimethyl glycine (DMG), and sarcosine catabolism genes and showed their efficient use as carbon and energy sources by marine halophilic vibrios.