COMPARATIVE-STUDY OF 5 POLYCYCLIC AROMATIC HYDROCARBON-DEGRADING BACTERIAL STRAINS ISOLATED FROM CONTAMINATED SOILS

Five polycyclic aromatic hydrocarbon (PAH) degrading bacterial strains , Pseudomonas putida 34, Pseudomonas fluorescens 62, Pseudomonas aerug inosa 57, Sphingomonas sp. strain 107, and the unidentified strain PL1 , were isolated from two contaminated soils and characterized for spec ific features regarding PAH degradation. Degradation efficiency was de termined by the rapidity to form clearing zones around colonies when s prayed with different PAH solutions and the growth in liquid medium wi th different PAHs as sole source of carbon and energy. The presence of plasmids, the production of biosurfactants, the effect of salicylate on PAH degradation, the transformation of indole to indigo indicating the presence of an aromatic ring dioxygenase activity, and the hybridi zation with the SphAb probe representing a sequence highly homologous to the naphthalene dioxygenase ferredoxin gene nahAb were examined. Th e most efficient strain in terms of substrate specificity and rapidity to degrade different PAHs was Sphingomonas sp. strain 107, followed b y strain PL1 and P. aeruginosa 57. The less efficient strains were P. putida 34 and P. fluorescens 62. Each strain transformed indole to ind igo, except strain PL1. Biosurfactants were produced by P. aeruginosa 57 and P. putida 34, and a bioemulsifier was produced by Sphingomonas sp. strain 107. The presence of salicylate in solid medium has acceler ated the formation of clearing zones and the transformation of indole by Sphingomonas sp. strain 107 and P. aeruginosa 57 colonies. Plasmids were found in Sphingomonas sp. strain 107 and strain PL1. The SphAb p robe hybridized with DNA extracted from each strain. However, hybridiz ation signals were detected only in the plasmidic fraction of Sphingom onas sp. strain 107 and strain PL1. Using a polymerase chain reaction (PCR) approach, we determined that several genes encoding enzymes invo lved in the upper catabolic pathway of naphthalene were present in eac h strain. Sequencing of PCR DNA fragments revealed that, for all the f ive strains, these genes are highly homologous with respective genes f ound in the pah, dox, and nah operons, and are arranged in a polycistr onic operon. Results suggest that these genes are ordered in the five selected strains like the pah, nah, and dox operons.