H. Derore et al., EVOLUTION OF HEAVY-METAL RESISTANT TRANSCONJUGANTS IN A SOIL ENVIRONMENT WITH A CONCOMITANT SELECTIVE PRESSURE, FEMS microbiology, ecology, 14(3), 1994, pp. 263-273
Conjugal transfer between Escherichia coli and Alcaligenes eutrophus o
f plasmid pDN705, containing genes encoding resistance against cadmium
, zinc and cobalt (czc genes) occurred in heavy metal polluted soil. T
he selective pressure from heavy metals (especially Zn2+) resulted in
an increased number of resistant transconjugants and higher respirator
y activities in sterile soil. As filter matings showed no or even a ne
gative effect of Zn2+ on plasmid transfer, the increase of the number
of transconjugants in polluted was probably due to growth rather than
stimulated transfer. High numbers of recipients inhibited extended gro
wth of transconjugants in sterile unpolluted soil. This intraspecific
competition was overcome in the presence of heavy metals. In non-steri
le soil, such an effect of heavy metals was not always, evident, and s
eemed to be related to the severity of the selective pressure and inve
rsely to the overall biological competition.