Identification of aerobic heterotrophic bacteria from the photic zone of a hypersaline microbial mat

Aerobic heterotrophic bacteria inhabiting microbial mats play an important role in carbon-cycling, yet information about their identity is scarce. We used the most probable number technique combined with denaturing gradient gel electrophoresis (DGGE) to identify apparent numerically important populations of aerobic heterotrophic bacteria in a hypersaline microbial mat. At high dilutions, populations related to the genera Rhodobacter and Roseobacter and to the genera Marinobacter and Halomonas dominated glycolate and yeast extract-amended enrichment cultures respectively. Three selected isolates of aerobic heterotrophic bacteria were obtained from glycolate-amended enrichments and found to relate phylogenetically to species of the genus Roseobacter. These strains were found to grow, in addition to glycolate, on several other photosynthetic compounds known to be produced by cyanobacteria suggesting that they specialize in mineralizing photosynthetic excretion products. Our study demonstrates that aerobic heterotrophs, which are phylogenetically affiliated to genera such as Rhodobacter, Roseobacter, Marinobacter and Halomonas, are important in hypersaline microbial mats, and that their specific in situ role in the carbon cycle needs to be further investigated.