Porphyromonas gingivalis mutant defective in a putative extracytoplasmic function sigma factor shows a mutator phenotype.
BACKGROUND
Porphyromonas gingivalis is implicated as a major pathogen in the development and progression of chronic periodontitis. P. gingivalis must possess the ability to tolerate stress signals outside the cytoplasmic membrane by transcriptional activation of genes encoding proteins involved in defense or repair processes. Some bacteria utilize a distinct subfamily of sigma factors to regulate extracytoplasmic function (hence termed the ECF subfamily).


METHODS
To elucidate their role in P. gingivalis, a chromosomal mutant carrying a disruption of an ECF sigma factor PG1318-encoding gene was constructed. Hemagglutination and proteolytic activities were measured in the PG1318-defective mutant. Reverse transcription-polymerase chain reaction (RT-PCR) analysis and southern blot analysis were used to assess transcription of kgp in the PG1318-defective mutant. Frequency of spontaneous mutation that conferred resistance to l-trifluoromethionine was measured in the PG1318-defective mutant.


RESULTS
The PG1318-defective mutant formed non-pigmented colonies on blood agar plates at a relatively high frequency. Arginine-specific and lysine-specific proteinase activities of the non-pigmented variants were remarkably decreased compared with those of the parent strain and the pigmented variants. RT-PCR analysis showed that kgp was not transcribed in some non-pigmented variants and southern blot analysis revealed that there was a deletion in their kgp region. Frequency of mutation conferring resistance to l-trifluoromethionine was significantly higher in the PG1318-defective mutant than in the wild-type.


CONCLUSIONS
These results suggest that PG1318 plays a role in the regulation of mutation frequency in the bacterium.
Kikuchi
Y
Y
Department of Oral Microbiology, Matsumoto Dental University, Shiojiri, Japan.
Ohara
N
N
Ueda
O
O
Hirai
K
K
Shibata
Y
Y
Nakayama
K
K
Fujimura
S
S
D018829:Adhesins, Bacterial / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D015139:Blotting, Southern; D055113:Chronic Periodontitis / Q000382:microbiology; D003546:Cysteine Endopeptidases / Q000235:genetics; D000080867:Gingipain Cysteine Endopeptidases; D006388:Hemagglutinins / Q000235:genetics; D006801:Humans; D008715:Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D016966:Porphyromonas gingivalis / Q000187:drug effects / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012808:Sigma Factor / Q000235:genetics*
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D000080867:Gingipain Cysteine Endopeptidases; D006388:Hemagglutinins; D012808:Sigma Factor; C037646:trifluoromethionine; D008715:Methionine; D003546:Cysteine Endopeptidases; C117151:KGP-381 protein, Porphyromonas gingivalis