Salt adaptation in pseudomonads: Characterization of glucosylglycerol-synthesizing isolates from brackish coastal waters and the rhizosphere

The compatible solute glucosylglycerol (GG) is widespread among cyanobacter ia, bur, until now, has been reported for only two species of heterotrophic bacteria. About 120 bacterial isolates from coastal regions of the Baltic Sea were screened by HPLC for their ability to synthesize GG. Positive isol ates (26) were grouped by SDS-PAGE of whole-cell proteins and representativ e strains of each group were investigated by sequencing their 16S rRNA gene s and phenotypic characterization. All GG-synthesizing isolates were shown to belong to the genus Pseudomonas (sensu stricto) and were assigned to 4 d istinct groups, although none of the GG-synthesizing isolates could be unam biguously assigned to described species. The identity of GG was verified by C-13 NMR analysis and enzymatic digestion with alpha- and beta-glucosidase s. Besides GG, salt adapted cultures of the aquatic isolates accumulated th e dipeptide N-acetylglutaminylglutamine amide (NAGGN) and glutamate. The ac cumulation of noncharged compatible solutes was also tested in previously i dentified pseudomonads isolated from the rhizosphere of oilseed rape and po tato. The majority of these strains were fluorescent species of the genus P seudomonas and accumulated trehalose and NAGGN when grown under salt stress conditions. However, rhizosphere isolates of Stenotrophomonas maltophilia synthesized GG and trehalose or only trehalose in a strain-dependent manner . These data indicate that the ability to synthesize GG is widely distribut ed among slightly or moderately halotolerant pseudomonads.