Dataset of phage genes in Bacillus subtilis 168

Under unfavourable circumstances,
bacteriophages that have infected a bacterial cell will undergo the lysogeny
cycle. During this process, the phage genome is integrated into the host
genome, with the molecular logic that the phage genome would be excised by
excisionase when circumstances turn for the better as the phage enters the lytic
cycle. Phage genes integrated into the host genome do not serve a useful
function for the host cells, and are thus subjected to greater evolutionary
pressure compared to host genes. Progressive rounds of mutations and sequence
drift may thus abrogate the utility and function of the phage genes, which if
repeated to many genes in the phage genome, may lead to inactivation of the
prophage, with the understanding that they are no longer able to enter the
lytic cycle. Besides the above, random insertion of transposon also disrupt the
function of phage genes, and may even replace them with structural genes from
the host genome. This work sought to profile and categorize the phage genes
present in Bacillus subtilis 168 genome for understanding how
evolutionary forces have shaped the evolution of prophages and their host.
Examination of the annotated genome of B. subtilis 168 revealed the
presence of 5 prophages. In each set of phage genes, substantial amount of
evidence points to the disruption of phage genes by the action of transposons.
Such effects manifest in the form of insertion of insertion element (IS) into
phage genes, or the swapping of phage genes with structural genes from the
host. Given the substantial number of phage genes that have been disrupted or
replaced, many of the prophages in B. subtilis have been inactivated.
But, this does not mean the evolutionary story stops here, continued presence
of the phage genes in the genome of the bacterial host provides loci for the
movement of host structural genes, and may represent a source of gene
amplification that may have as-yet unknown effects on the host cell fitness in
particular environment.