Natural transformation of indigenous marine bacteria
has been demonstrated by Frischer et al. (1994) using
plasmid multimers of pQSR50. Plasmid multimers were
used to ensure internal homology and thus provide a site
for self-homologous recombination. The ambient microbial
communities in water column samples (20 L) or coral
mucus (1 L) were first concentrated to approx. 50 ml and 1
ml used in filter transformation assays. For sediments and
bacteria in sponge tissue, the bacteria were extracted
mechanically and then used in filter transformation assays.
Transformation was assessed as expression of the
antibiotic resistance genes encoded by the plasmid in
combination with confirmation by molecular probing.
However, certain environments contained indigenous
marine bacteria that possessed sequences that hybridized
with the probe used and any such environments were not
considered further. Positive transformation was found in 5
of 13 experiments, with transfer frequencies ranging from
3.6x10-6 to 1.13x10-9. In all cases of plasmid transfer to
the natural community, restriction profiles from
transformants were altered when compared to the parent
plasmid. Differences in the recovered transformant
plasmids were accounted for by difference in methylation
compared to the parent plasmid, as well as some genetic
rearrangement (Williams et al., 1997). Thus, transfer to
the indigenous flora, at least when considering plasmid
DNA, can result in rearrangement and alteration of the
DNA, contributing to plasmid and recipient evolution.