Utilization of the compatible solutes sucrose and trehalose by purple sulfur and nonsulfur bacteria

Owing to their ubiquity as compatible solutes, sucrose and trehalose and th eir constituent monosaccharides, glucose and fructose, may represent a sign ificant source of carbon for the growth of other bacteria. We investigated sugar utilization by 34 strains of purple sulfur and nonsulfur bacteria iso lated from coastal lagoons. Amongst the purple nonsulfur bacteria, sugar ut ilization was common with almost all strains utilizing the tested monosacch arides and 70 and 50% of strains utilizing sucrose and trehalose, respectiv ely. Sugar utilization was rarer amongst the purple sulfur bacteria, with n one of the strains using glucose or trehalose. Fructose, was utilized by 50 % of isolates and sucrose was utilized only by strains of Thiorhodococcus. Surprisingly, although unable to use glucose directly, Thiorhodococcus stra ins used both the glucose and fructose moieties of sucrose and utilized glu cose slowly in the presence of fructose, indicating that these strains may be impaired in glucose transport, rather than glucose metabolism per se. Di saccharide metabolism was dependent on sugar uptake and none of the strains produced trehalases or sucrases. Efficacy of sugar utilization varied wide ly with specific growth yield between 0.09 and 0.78 g dry weight-g sugar(-1 ), and was dependent upon both the sugar and the strain. Similarly, specifi c growth rates were highly variable with strain and the sugar present and r anged between 5.4 and 0.5 x 10(-2) .h(-1). Overall, data indicate that in natural high salinity ecosystems, purple sul fur and particularly purple nonsulfur bacteria may be able to efficiently e xploit compatible solutes released to the environment by other members of t he bacterial community.