Alternative Sigma Factor B in Bovine Mastitis-Causing : Characterization of Its Role in Biofilm Formation, Resistance to Hydrogen Peroxide Stress, Regulon Members

This study examines treatments of the bacterial pathogen , namely, in the context of its being a major cause of subclinical bovine mastitis. Such infections caused by among dairy cows are difficult to detect and can easily become chronic, leading to reduced productivity and large losses for dairy manufacturers. In this study, the role of alternative sigma factor B (σ), which has been shown to be a global regulator for infections, was explored in a mastitis-causing strain, RF122. For comparison with the wild-type strain, a null (Δ) mutant was constructed and analyzed for its phenotypes and transcriptome. Our study found that σ is essential for biofilm formation as the Δ mutant strain produced significantly less biofilm than did the wild-type strain at 48 h. σ is involved in response to HO stress. However, σ plays a minor or no role in resistance to antiseptics (e.g., povidone-iodine and chlorhexidine), resistance to tested antibiotics, hemolysin activity, and invasion ability. RNA sequencing identified 225 σ-dependent genes, of which 171 are positively regulated and 54 are negatively regulated. The identified genes are involved in stress response, pathogenesis, and metabolic mechanisms. Quantitative TaqMan RT-PCR was performed to verify the RNA sequencing results; i.e., σ is a positive regulator for , and expressions. In the RF122 strain, σ plays a role in biofilm formation, general stress response (e.g., HO), and regulation of virulence factors and virulence-associated genes.