Frequency of horizontal gene transfer of a large catabolic plasmid (pJP4) in soil

Abstract

Limited work has been done to assess the bioremediation potential of transfer of plasmid-borne degradative genes from introduced to indigenous organisms in the environment. Here we demonstrate the transfer by conjugation of the catabolic plasmid pJP4, using a model system with donor and recipient organisms. The donor organism was Alealigenes eutrophus JMP134 and the recipient organism was Variovorax paradoxus isolated from a toxic waste site. Plasmid pJP4 contains genes for mercury resistance and 2,4-dichlorophenoxyacetic (2,4-D) acid degradation. A transfer frequency of approximately 1/103 donor and recipient cells (parent cells) was observed on solid agar media, decreasing to 1/105 parent cells in sterile soil and finally 1/106 parent cells in 2,4-D-amended, nonsterile soil. Presumptive transconjugants were confirmed to be resistant to Hg, to be capable of degrading 2,4-D, and to contain a plasmid of size comparable to that of pJP4. In addition, we confirmed the transfer through PCR amplifications of the tfdB gene. Although transfer of pJP4 did occur at a high frequency in pure culture, the rate was significantly decreased by the introduction of abiotic (sterile soil) and biotic (nonsterile soil) stresses. An evaluation of the data from this model system implies that the reliance on plasmid transfer from a donor organism as a remediative strategy has limited potential.

Long-term dynamics of catabolic plasmids introduced to a microbial community in a polluted environment: a mathematical model

“…Therefore, as a bioaugmentation strategy, the horizontal transfer of catabolic plasmids from an introduced donor host into actively growing indigenous bacteria via conjugation, and the subsequent gene expression have been widely studied since the early 1990s (Fulthorpe & Wyndham, 1991;Bathe et al, 2004aBathe et al, , 2005. Most previous studies have focussed on the conditions required for an initial increase in transconjugants (for a review see van Elsas & Bailey, 2002): a nonsterile environment for rapid growth of recipient and donor bacteria to promote frequent conjugation (Top et al, 1990;Neilson et al, 1994), a sufficiently high transfer rate per conjugation (Neilson et al, 1994), a broad host range for plasmids Bathe et al, 2004b), effective gene expression in transconjugants (Kinkle et al, 1993), and a high concentration of the pollutant to create a selective advantage for plasmid-bearing bacteria over other indigenous bacteria (Top et al, 1998;Hohnstock et al, 2000;de Lipthay et al, 2001). These conditions are indicated by the short-term dynamics of plasmids after the introduction of extrinsic donor bacteria; the short-term dynamics of plasmids result in a decrease in the introduced donor bacteria and an increase in transconjugants because of competition and a reduction in the concentration of the xenobiotic (e.g.…”

System to study horizontal gene exchange among microorganisms without cultivation of recipients

“…Although it is well established that plasmids and transposons play a critical role in moving functional gene blocks between bacteria (Neilson et al, 1994), the evolution of such gene blocks encoding new activities is poorly understood. Experimentally, it is reasonably straightforward to clone appropriate genes from different organisms, to select variants of such genes that confer new phenotypes, to combine the genes in appropriate sequences under the control of effective regulatory circuits and to fine-tune their expression .…”

High phylogenetic diversity of transconjugants carrying plasmid pJP4 in an activated sludge-derived microbial community

“…Fig. 1 shows a phylogenetic tree constructed from partial 16S rDNA sequences of transconjugants isolated in this study, closely related sequences and sequences of previously described pJP4 transconjugant species [1,5,[19][20][21][22][23][24][25]. The pJP4 transconjugants isolated and sequenced in this experiment showed a broad taxonomic distribution within the a-, b-, cb-, and c-Proteobacteria, and belonged mainly to Rhizobiaceae, Comamonadaceae families, and genus Stenotrophomonas.…”