Compatible solutes in luminescent bacteria of the genera Vibrio, Photobacterium and Photorhabdus (Xenorhabdus): occurrence of ectoine, betaine and glutamate

Abstract Marine luminescent bacteria of the genera Vibrio and Photobacterium as well as Photorhabdus (Xenorhabdus) luminescens , an enterobacterium mutualistically associated with insect pathogenic soil nematodes, display different levels of salt tolerance when grown on nutrient broth medium (5% w/v NaCl for marine species and 3% w/v for Prb. luminescens ). Osmolytes (compatible solutes) synthesized and/or accumulated for haloadaptation were identified using HPLC techniques and 13 C-NMR spectroscopy. All species investigated in this study accumulated betaine and ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) from the medium under elevated osmotic conditions. External supply of osmolytes improved both growth and salt tolerance. Only species belonging to the genus Vibrio were able to synthesize the compatible solute ectoine de novo. Glutamate also participated in osmoadaptation while trehalose was only found in V. fischeri species. In Prb. luminescens 13 C-NMR spectroscopy also revealed the presence of choline when grown on complex medium.