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

Abstract

Owing to their ubiquity as compatible solutes, sucrose and trehalose and their constituent monosaccharides, glucose and fructose, may represent a significant source of carbon for the growth of other bacteria. We investigated sugar utilization by 34 strains of purple sulfur and nonsulfur bacteria isolated from coastal lagoons. Amongst the purple nonsulfur bacteria, sugar utilization was common with almost all strains utilizing the tested monosaccharides and 70 and 50% of strains utilizing sucrose and trehalose, respectively. Sugar utilization was rarer amongst the purple sulfur bacteria, with none 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 strains used both the glucose and fructose moieties of sucrose and utilized glucose slowly in the presence of fructose, indicating that these strains may be impaired in glucose transport, rather than glucose metabolism per se. Disaccharide metabolism was dependent on sugar uptake and none of the strains produced trehalases or sucrases. Efficacy of sugar utilization varied widely 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, specific growth rates were highly variable with strain and the sugar present and ranged between 5.4 and 0.5 × 10-2·h-1.Overall, data indicate that in natural high salinity ecosystems, purple sulfur and particularly purple nonsulfur bacteria may be able to efficiently exploit compatible solutes released to the environment by other members of the bacterial community.Key words: Chromatiaceae, purple sulfur bacteria, purple nonsulfur bacteria, sugar utilization.