Mycobacterium diversity and pyrene mineralization in petroleum-contaminated soils

Degradative strains of fast-growing Mycobacterium spp. are commonly isolate d from polycyclic aromatic hydrocarbon (PAH)-contaminated soils. Little is known, however, about the ecology and diversity of indigenous populations o f these fast-growing mycobacteria in contaminated environments, In the pres ent study 16S rRNA genes were PCR amplified using Mycobacterium-specific pr imers and separated by temperature gradient gel electrophoresis (TGGE), and prominent bands were sequenced to compare the indigenous Mycobacterium com munity structures in four pairs of soil samples taken from heavily contamin ated and less contaminated areas at four different sites. Overall, TGGE pro files obtained from heavily contaminated soils were less diverse than those from less contaminated soils. This decrease in diversity may be due to tox icity, since significantly fewer Mycobacterium phylotypes were detected in soils determined to be toxic by the Microtox assay than in nontoxic soils. Sequencing and phylogenetic analysis of prominent TGCE bands indicated that novel strains dominated the soil Mycobacterium community, Mineralization s tudies using [C-14]pyrene added to four petroleum-contaminated soils, with and without the addition of the known pyrene degrader Mycobacterium sp, str ain RJGII-135, indicated that inoculation increased the level of degradatio n in three of the four soils. Mineralization results obtained from a steril ized soil inoculated with strain RJGII-135 suggested that competition with indigenous microorganisms may be a significant factor affecting biodegradat ion of PAHs. Pyrene-amended soils, with and without inoculation with strain RJGII-135, experienced both increases and decreases in the population size s of the inoculated strain and indigenous Mycobacterium populations during incubation.