Analysis of the relative abundance of different types of bacteria capable of toluene degradation in a compost biofilter

A microbial community of a compost biofilter treating toluene vapors was in vestigated using serum-bottle assays and mineral-agar plates. Toluene was n ot consumed in the absence of oxygen. However, filter-bed extracts exposed to toluene vapor as the only carbon source produced distinct colony types ( phenotypic groups) that were counted separately. Strains from each group we re isolated and checked for toluene-degradation activity in serum bottles. Only 15% of colonies were true toluene degraders. This population was divid ed into 11 genotypic groups based on DNA fingerprints. Identification of a member of each group using 16S rRNA gene-sequence comparison showed that th ey belonged to seven genera: Acinctohncter, Azoarcus! Mycobacterium , Nevsk ia, Pseudomonas, Pseudonocardia and Rhodococcus. Together, members of the g enera Pseudonocardia and Rhodococcus were 34 times more numerous than all t he others. We hypothesized that these two organisms are K-strategists (adap ted to a resource and crowded environment) and that the compost biofilter i s a K-environment. This would explain why they are not outnumbered by faste r growers like Pseudomonas or Acinetobacter species, which would be r-strat egists (adapted to a resource-abundant and uncrowded environment).