Composition of toluene-degrading microbial communities from soil at different concentrations of toluene

Toluene-degrading bacteria were isolated from hydrocarbon-contaminated soil by incubating liquid enrichment cultures and agar plate cultures in desicc ators in which the vapor pressure of toluene was controlled by dilution wit h vacuum pump oil. Incubation in desiccators equilibrated with either 100, 10, or 1% (wt/wt) toluene in vacuum pump oil and testing for genomic cross- hybridization resulted in four genomically distinct strains (standards) cap able of growth on toluene (strains Cstd1, Cstd2, Cstd5, and Cstd7). The opt imal toluene concentrations for growth of these standards on plating media differed considerably. Cstd1 grew best in an atmosphere equilibrated with 0 .1% (wt/wt) toluene, but Cstd5 failed to grow in this atmosphere, Conversel y, Cstd5 grew well in the presence of 10% (wt/wt) toluene, which inhibited growth of Cstd1. 16S ribosomal DNA sequencing and cross-hybridization analy sis indicated that both Cstd1 and Cstd5 are members of the genus Pseudomona s. An analysis of the microbial communities in soil samples that mere incub ated with 10% (wt/wt) toluene with reverse sample genome probing indicated that Pseudomonas strain Cstd5 was the dominant community member. However, i ncubation of soil samples with 0.1% (wt/wt) toluene resulted in a community that was dominated by Pseudomonas strain Q7, a toluene degrader that has b een described previously (Y. Shen, L. G. Stehmeier, and G. Voordouw, Appl. Environ. Microbiol. 64:637-645, 1998). Q7 was not able to grow by itself in an atmosphere equilibrated with 0.1% (wt/wt) toluene but grew efficiently in coculture with Cstd1, suggesting that toluene or metabolic derivatives o f toluene were transferred from Cstd1 to Q7.