Nucleoid-Associated Rok Differentially Affects Chromosomal Transformation On Bacillus Subtilis Recombination-Deficient Cells

Rok, a Bacillus subtilis nucleoid-associated protein (NAP), negatively regulates competence development and silences xenogeneic genes. We show that rok inactivation increases rpoB482 natural intraspecies chromosomal transformation (CT) and plasmid transformation to a different extent. In Delta addAB, Delta recO, recF15, Delta recU, Delta ruvAB or rec(+) cells intraspecies CT significantly increases, but the Delta recD2 mutation reduces, and the Delta recX, Delta radA or Delta dprA mutation further decreases CT in the Delta rok context when compared to rok(+) cells. These observations support the idea that rok inactivation, by altering the topology of the recipient DNA, differentially affects the integration of homologous DNA in rec-deficient strains, and in minor extent the competent subpopulation size. The impairment of other NAP (Hbsu or LrpC) also increased intra- and interspecies CT (nonself-DNA, ~8% nucleotide sequence divergence) in rec(+) cells, but differentially reduced both types of CTs in certain rec-deficient strains. We describe that rok inactivation significantly stimulates intra and interspecies CT but differentially reduces them in transformation-deficient cells, perhaps by altering the nucleoid architecture. We extend the observation to other NAPs (Hbsu, LrpC).