Whereas the capability of DNA uptake has been well established for numerous
species and strains of bacteria grown in vitro, the broader distribution of natural
transformability within bacterial communities remains largely unexplored.
Here, we investigate the ability of bacterial isolates from the gut of grass
grub larvae (Costelytra zealandica (White); Coleoptera: Scarabaeidae) to develop natural genetic competence in vitro. A total
of 37 mostly species-divergent strains isolated from the gut of grass grub
larvae were selected for spontaneous rifampicin-resistance. Genomic DNA was
subsequently isolated from the resistant strains and exposed to sensitive
strains grown individually using established filter transformation
protocols. DNA isolated from wild-type strains was used as a control. None
of the 37 isolates tested exhibited a frequency of conversion to
rifampicin-resistance in the presence of DNA at rates that were
significantly higher than the rate of spontaneous mutation to
rifampicin-resistance in the presence of wild-type DNA (the limit of
detection was approximately < 1 culturable transformant per 109 exposed bacteria). To further examine if conditions were conducive to
bacterial DNA uptake in the grass grubs gut, we employed the competent
bacterium Acinetobacter baylyi strain BD413 as a recipient species for in vivo studies. However, no
transformants could be detected above the detection limit of 1 transformant
per 103 cells, possibly due to low population density and limited
growth of A. baylyi cells in grass grub guts. PCR analysis indicated that chromosomal Acinetobacter
DNA remains detectable by PCR for up to 3 days after direct inoculation into
the alimentary tract of grass grub larvae. Nevertheless, neither
transforming activity of the DNA recovered from the alimentary tract of
grass grubs larvae nor competence of bacterial cells recovered from
inoculated larvae could be shown.