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Abstract
Porphyromonas gingivalis is a bacterium frequently isolated from chronic periodontal lesions and is involved in the development of chronic periodontitis. To colonize the gingival crevice, P. gingivalis has to adapt to environmental stresses. Microbial gene expression is regulated by transcription factors such as those in two-component systems and extracytoplasmic function (ECF) sigma factors. ECF sigma factors are involved in the regulation of environmental stress response genes; however, the roles of individual ECF sigma factors are largely unknown. The purpose of this study was to investigate the functions, including autoaggregation, hemagglutination, gingipain activity, susceptibility to antimicrobial agents, and surface structure formation, of P. gingivalis ECF sigma factors encoded by SigP (PGN_0274), SigCH (PGN_0319), PGN_0450, PGN_0970, and SigH (PGN_1740). Various physiological aspects of the sigP mutant were affected; autoaggregation was significantly decreased at 60 min (p < 0.001), hemagglutination activity was markedly reduced, and enzymatic activities of Kgp and Rgps were significantly decreased (p < 0.001). The other mutants also showed approximately 50% reduction in Rgps activity. Kgp activity was significantly reduced in the sigH mutant (p < 0.001). No significant differences in susceptibilities to tetracycline and ofloxacin were observed in the mutants compared to those of the wild-type strain. However, the sigP mutant displayed an increased susceptibility to ampicillin, whereas the PGN_0450 and sigH mutants showed reduced susceptibility. Transmission electron microscopy images revealed increased levels of outer membrane vesicles formed at the cell surfaces of the sigP mutant. These results indicate that SigP is important for bacterial surface-associated activities, including gingipain activity, autoaggregation, hemagglutination, vesicle formation, and antimicrobial susceptibility.
Highlights
Bacteria are exposed to physiological stresses such as temperature, oxygen tension, and pH in natural environments that they inhabit
We compared the autoaggregation of wild-type cells and Extracytoplasmic function (ECF) sigma factor mutants to determine whether ECF sigma factors modulate cell wall architecture
We determined that autoaggregation, hemagglutination, gingipain activities, and outer membrane vesicles (OMVs) formation, which all contribute to P. gingivalis virulence, were altered in the sigP mutant
Summary
Bacteria are exposed to physiological stresses such as temperature, oxygen tension, and pH in natural environments that they inhabit. They adapt to these environmental stresses using multiple regulatory pathways [1, 2]. Porphyromonas gingivalis is a Gram-negative anaerobic bacterium frequently isolated, together with Treponema denticola and Tannerella forsythia, from human chronic periodontal lesions [6]. This microorganism produces cell surface-associated virulence factors, such as cysteine proteases (gingipains), lipopolysaccharides, and fimbriae [7,8,9], and can invade epithelial cells [10]. Six putative ECF sigma factors, namely, PGN_0274, PGN_0319, PGN_0450, PGN_0970, PGN_1108, and PGN_1740, were identified in the genome of P. gingivalis ATCC 33277 (GenBank: AP009380) [12]
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