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.

A new staphylococcal phage, P4-2, which could convert the capability of producing staphylokinase, was isolated. The phage is different from the phage reported by Winkler and co-workers [Nature(London) 195:407-408, 1962; J. Gen. Microbiol. 39:321-333, 1965]. The former is a single-converting phage belonging to serotype B, but the latter is a serotype F phage capable of converting not only staphylokinase but also beta-hemolysin. Staphylokinase, i.e., the fibrinolysin produced by Staphylococcus aureus, therefore, can now be classified into three types. One is controlled by the genes on the bacterial chromosome, and the other two are mediated by lysogenic conversion by prophage PO-2 and the classical phage reported by Winkler and co-workers.It has become well known since the reports of Winkler and co-workers (2, 10) that staphylococcal phage belonging to serotype F can convert two biological characteristics of lysogenized cells (2, 10). One characteristic is production of beta-hemolysin (,8H) and the other is production of fibrinolysin, or the so-called staphylokinase (SAK). The former is converted from positive to negative, whereas the latter is converted from negative to positive.We have recently devised a simple and effective method to remove prophage from lysogenic staphylococci (5, 7). It is comprised of ultraviolet (UV) irradiation of the strain in question followed by treatment with ethidium bromide or acriflavine.As is widely known, almost all the clinically isolated strains of Staphylococcus aureus are lysogenic, a majority of which produce SAK but not ,1H. Since the strain carrying a prophage of the Winkler type should present the same pattern of characteristics as mentioned above, it is also likely that there are many staphylococcal strains lysogenic to a phage of this type in the clinical strains.The new phage in this paper was detected during the course of testing, by means of the delysogenization method, whether our above assumption is correct.The present paper describes details of the process of isolating this phage and the results of characterization of the phage and SAK production under the control of this phage. MATERIALS AND METHODSBacterial strains. S. aureus 20 and 406 were chiefly used. The former strain was kindly supplied by the