The diversity of extradiol dioxygenase (edo) genes in cresol degrading rhodococci from a creosote-contaminated site that express a wide range of degradative abilities

Analysis of the bacterial population of soil surface samples from a creosot e-contaminated site showed that up to 50% of the culturable micro-organisms detected were able to utilise a mixture of cresols. From fifty different m icrobial isolates fourteen that could utilise more than one cresol isomer w ere selected and identified by 16S rRNA analysis. Eight isolates were Rhodo coccus strains and six were Pseudomonas strains. In general, the Rhodococcu s strains exhibited a broader growth substrate range than the Pseudomonas s trains. The distribution of various extradiol dioxygenase (edo) genes, prev iously associated with aromatic compound degradation in rhodococci, was det ermined for the Rhodococcus strains by PCR detection and Southern-blot hybr idization. One strain, Rhodococcus sp. I1 exhibited the broadest growth sub strate range and possessed five different edo genes. Gene disruption experi ments indicated that two genes (edoC and edoD) were associated with isoprop ylbenzene and naphthalene catabolism respectively. The other Rhodococcus st rains also possessed some of the edo genes and one (edoB) was present in al l of the Rhodococcus strains analysed. None of the rhodococcal edo genes an alysed were present in the Pseudomonas strains isolated from the site. It w as concluded that individual strains of Rhodococcus possess a wide degradat ive ability and may be very important in the degradation of complex mixture s of substrates found in creosote.