Complete sequence of Bacillus subtilis plasmid p1414 and comparison with seven other plasmid types found in Russian...

We determined the complete sequence of a cryptic 7949-bp plasmid isolated from naturally occurring Bacillus subtilis found in Russian soil from Moscow. We found 15 putative open reading frames (ORFs), all of which were preceded by a ribosome binding site. One encodes the gene (rep) which should be essential for vegetative rolling circle replication (RCR). The putative double-stranded origin as well as a palT1-like single-stranded origin was also identified. The predicted product of another ORF showed similarity to a moblization protein while a third showed similarity to a ubiquitous family of small proteins whose members have so far been associated with stress response. We used fragments with these latter ORFs to probe representatives of seven other groups of cryptic RCR plasmids from geographically related B. subtilis isolates. All plasmids carried the mob function, suggesting a common ancestor for the rep/mob region but the putative hsp was present only on some of the plasmids. This suggests that the putative hsp gene is not an essential plasmid component and may therefore be present as a phenotypic marker-perhaps providing response to stress. This adds weight to the growing evidence that these small Bacillus plasmids may not be cryptic but may provide an adaptive advantage for the host in its natural environment.