Low-Frequency Horizontal Transfer of an Element Containing the Chlorocatechol Degradation Genes from Pseudomonas sp. Strain B13 to Pseudomonas putida F1 and to Indigenous Bacteria in Laboratory-Scale Activated-Sludge Microcosms

Abstract

The possibilities for low-frequency horizontal transfer of the self-transmissible chlorocatechol degradative genes (clc) from Pseudomonas sp. strain B13 were investigated in activated-sludge microcosms. When the clc genes were transferred into an appropriate recipient bacterium such as Pseudomonas putida F1, a new metabolic pathway for chlorobenzene degradation was formed by complementation which could be selected for by the addition of mono-or 1,4-dichlorobenzene (CB). Under optimized conditions with direct donor-recipient filter matings, very low transfer frequencies were observed (approximately 3.5 ؋ 10 ؊8 per donor per 24 h). In contrast, in matings on agar plate surfaces, transconjugants started to appear after 8 to 10 days, and their numbers then increased during prolonged continuous incubation with CB. In activated-sludge microcosms, CB-degrading (CB ؉ ) transconjugants of strain F1 which had acquired the clc genes were detected but only when strain B13 cell densities of more than 10 5 CFU/ml could be maintained by the addition of its specific growth substrate, 3-chlorobenzoate (3CBA). The CB ؉ transconjugants reached final cell densities of between 10 2 and 10 3 CFU/ml. When strain B13 was inoculated separately (without the designated recipient strain F1) into an activated-sludge microcosm, CB ؉ transconjugants could not be detected. However, in this case a new 3CBA-degrading strain appeared which had acquired the clc genes from strain B13. The effects of selective substrates on the survival and growth of and gene transfer between bacteria degrading aromatic pollutants in a wastewater ecosystem are discussed.

Enhanced degradation of phenoxyacetic acid in soil by horizontal transfer of the tfdA gene encoding a 2,4-dichlorophenoxyacetic acid dioxygenase

“…[1,21,22]). The feasibility of complementing degradative pathways has been demonstrated by us [7,8] and others [23,24] with pure cultures but to the best of our knowledge only one other study has demonstrated an enhanced degradation rate of new compounds following complementation of existing pathways in situ [4]. Ravatn et al [4] showed that in situ horizontal transfer of chlorocatechol degradative genes to a toluene degrading recipient strain resulted in a new metabolic pathway for degradation of chlorobenzene.…”

“…The feasibility of complementing degradative pathways has been demonstrated by us [7,8] and others [23,24] with pure cultures but to the best of our knowledge only one other study has demonstrated an enhanced degradation rate of new compounds following complementation of existing pathways in situ [4]. Ravatn et al [4] showed that in situ horizontal transfer of chlorocatechol degradative genes to a toluene degrading recipient strain resulted in a new metabolic pathway for degradation of chlorobenzene. These results together with those presented here suggest that complementing catabolic capabilities by horizontal transfer of additional genes to indigenous microbial communities in contaminated sites is a possible approach to bioremediation that warrants further investigation and development.…”

RAPD-PCR typing of Acinetobacter isolates from activated sludge systems designed to remove phosphorus microbiologically

“…It is likely to be high, and strains resistant to other antibiotics are probably present there too. The opportunities for horizontal gene transfer must be present (Ravatn et al 1998), especially with plasmid DNA readily detected in activated sludge (e.g. Bauda et al 1995).…”

Dispersal of plasmid pJP4 in unsaturated and saturated 2,4-dichlorophenoxyacetic acid contaminated soil

“…In addition, enhanced remediation of contaminated soils as a result of such transfers has been documented [1,9,11,12]. Complementation of catabolic pathways via horizontal transfer of additional genes to indigenous microbial communities has also been shown to result in enhanced degradation [13,14]. However, these studies were generally conducted in batch microcosms with little work done to evaluate the transport, or dispersal, of introduced genes.…”