Molecular Mechanism for the Spontaneous Generation of Pigmentless Porphyromonas gingivalis Mutants

Porphyromonas gingivalis is one of the pathogens associated with periodontal diseases, and its protease activity has been implicated as an important virulence factor. Kgp is the major Lys-gingipain protease of P. gingivalis and appears to be involved not only in enzyme activity but also in hemagglutination and the pigmented phenotype due to heme accumulation and/or hemoglobin binding. However, little information concerning the molecular mechanism for the spontaneous generation of pigmentless P. gingivalis mutants is currently available. In this study, several spontaneous pigmentless mutants of P. gingivalis were isolated and characterized. The results revealed that a portion of the kgp gene had been deleted from the chromosomes of the pigmentless mutants. This deletion appears to result from recombination between the highly homologous DNA sequences encoding the adhesin domains of the tandemly arranged hagA and kgp genes on the chromosomes of P. gingivalis strains.