The response and adaptation of bacteria to environmental stress are known to be mostly regulated at the level of transcription initiation. This regulation primarily involves alternative sigma factors, which recruit RNA polymerase and facilitate specific promoter recognition and transcription initiation (Paget & Helmann, 2003). Extracytoplasmic function (ECF) sigma factor, the largest group of alternative sigma factors, plays a key role in adaption to environmental conditions (Staron et al., 2009). Furthermore, because bacteria–host Tacrolimus mw interaction via surface structures is important in bacterial pathogenesis, ECF sigma factors also regulate

virulence factors (Staron et al., 2009). This is well documented in Mycobacterium tuberculosis (Hahn et al., 2005), Staphylococcus aureus (Shaw et al., 2008), Pseudomonas aeruginosa (Llamas et al., 2009; Wood & Ohman, 2009), and Enterococcus faecalis (Le et al., 2010). Porphyromonas gingivalis, an anaerobic gram-negative bacterium, is an important etiological agent in adult chronic periodontitis. This

organism possesses several cell surface-associated virulence factors (e.g. hydrolytic enzymes, fimbriae, hemagglutinin, capsule, and lipopolysaccharide) that can directly or indirectly affect the periodontium (Yoshimura et al., 2009). In addition, to survive in the microenvironment of an advanced periodontal pocket, it is necessary that the bacteria have the capacity to respond to environmental changes including temperature, pH, the concentration of some nutrients, and oxygen tension. To date, little is known about the relationship between the regulation of adaptive mechanisms, virulence, and sigma factors in P. Bioactive Compound Library order gingivalis. The P. gingivalis W83 genome encodes eight sigma factors, six of which belong to the ECF sigma factor subfamily (PG0162, PG0214,

PG0985, PG1318, PG1660, and PG1827) (Nelson et al., 2003). The PG1318 ECF sigma factor was recently shown to be involved in the regulation of mutation frequency in P. gingivalis (Kikuchi et al., 2009). In this study, we used a PCR-based linear transformation strategy to inactivate the remaining five putative ECF sigma factors, GNAT2 and analyzed the virulence-related characteristics of these proteins in P. gingivalis W83. We now report that several of the ECF sigma factors may play a role in virulence regulation and adaptation to oxidative stress. ECF sigma factors encoded by the PG0162 and PG1660 genes are likely involved in the post-transcriptional regulation of the gingipains. The strains and plasmids used in this study are listed in Table 1. Porphyromonas gingivalis strains were grown in a Brain–Heart Infusion (BHI) broth supplemented with 0.5% yeast extract (Difco Laboratories, Detroit, MI), hemin (5 μg mL−1), vitamin K (0.5 μg mL−1), and cysteine (0.1%) (Sigma-Aldrich, St. Louis, MO). Porphyromonas gingivalis strains were maintained in an anaerobic chamber (Coy Manufacturing, Ann Arbor, MI) in 10% H2, 10% CO2, and 80% N2 at 37 °C. The growth rates for P.