Genetic exchange in soil between introduced chlorobenzoate degraders and indigenous biphenyl degraders

Abstract

Pseudomonas aeruginosa JB2, a chlorobenzoate degrader, was inoculated into soil having indigenous biphenyl degraders but no identifiable 2-chlorobenzoate (2CBa) or 2,5-dichlorobenzoate (2,5DCBa) degraders. The absence of any indigenous chlorobenzoate degraders was noted by the failure to obtain enrichment cultures with the addition of 2CBa, 3CBa, or 2,5DCBa and by the failure of soil DNA to hybridize to the tfdC gene, which encodes ortho fission of chlorocatechols. In contrast, DNA extracted from inoculated soils hybridized to this probe. Bacteria able to utilize both biphenyl and 2CBa as growth substrates were absent in uninoculated soil, but their presence increased with time in the inoculated soils. This increase was related kinetically to the growth of biphenyl degraders. Pseudomonas sp. strain AW, a dominant biphenyl degrader, was selected as a possible parental strain. Eight of nine recombinant strains, chosen at random, had high phenotypic similarity (90% or more) to the inoculant; the other, strain JB2-M, had 78% similarity. Two hybrid strains, P. aeruginosa JB2-3 and Pseudomonas sp. JB2-M, were the most effective of all strains, including strain AW, in metabolizing polychlorinated biphenyls (Aroclor 1242). Repetitive extragenic palindromic-PCR analysis of putative parental strains JB2 and AW and the two recombinant strains JB2-3 and JB2-M showed similar fragments among the recombinants and JB2 but not AW. These results indicate that the bph genes were transferred to the chlorobenzoate-degrading inoculant from indigenous biphenyl degraders.

Catabolic mobile genetic elements and their potential use in bioaugmentation of polluted soils and waters

“…It is however unknown until now if plasmids from non-culturable bacterial hosts have indeed been retrieved by using this method. One example of recruitment of indigenous catabolic genes in situ was reported by Focht et al [9]. They observed in situ acquisition of biphenyl degradation genes in soil by a chlorobenzoate degrading inoculant, yielding a polychlorinated biphenyl (PCB) degrader.…”

Characterization of chlorobenzoate degraders isolated from polychlorinated biphenyl-contaminated soil and sediment in the Czech Republic

“…The significance of the CB metabolic pathway for the degradation of PCBs has already been indicated (Fava et al 1993;Hickey et al 1993;Focht et al 1996). In our recent experiment focusing on the degradation of commercial PCB mixture Delor 103 by co-metabolizing biphenyl degraders we have noticed the accumulation of high amounts of orthochlorinated benzoates, namely 2,5-DCB, in a reaction mixture.…”

“…In particular, Brunsbach and Reineke (1993) showed that soils require inoculation with chlorobenzene degraders before the degradation will take place. Other studies showed that the inoculation of soil with chlorobenzoate degraders increased the mineralization of PCBs in soil more than the addition of chlorobiphenyl-co-metabolizing strains (Hickey et al 1993;Focht et al 1996). To our knowledge, there has not yet been a comprehensive study reflecting the diversity of the chlorobenzoate-degrading population on PCB-contaminated sites.…”

Effect of inoculation of a TOL plasmid containing mycorrhizosphere bacterium on development of Scots pine seedlings, their mycorrhizosphere and the microbial flora in m-toluate-amended soil

“…Conjugation in soil (and rhizosphere) between introduced donor and indigenous bacteria has been shown to occur in many studies (for review, see [10]). However, only in several studies, the transfer of catabolic genes and plasmids between introduced bacteria and indigenous soil bacteria [7,8,11,12] has been followed. None of these was performed in the rhizosphere.…”