Analysis of Kytococcus sedentarius Strain Isolated from a Dehumidifier Operating in a University Lecture Theatre: Systems for Aerobic Respiration, Resisting Osmotic Stress, and Sensing Nitric Oxide

A strain of Kytococcus sedentarius was isolated from a dehumidifier operating in a university lecture theatre. Genome analysis and phenotypic characterisation showed that this strain, K. sedentarius MBB13, was a moderately halotolerant aerobe with a branched aerobic electron transport chain and genes that could contribute to erythromycin resistance. The major compatible solute was glycine betaine, with ectoine and proline being deployed at higher osmolarities. Actinobacteria possess multiple WhiB-like (Wbl) regulatory proteins, and K. sedentarius MBB13 has four (WhiB1, WhiB2, WhiB3, and WhiB7). Wbls are iron-sulfur proteins that regulate gene expression through interactions with RNA polymerase sigma factors and/or other regulatory proteins. Bacterial two-hybrid analyses suggested that WhiB1 and WhiB2, but not WhiB3 and WhiB7, interact with the C-terminal domain of the major sigma factor, σ^A; no interaction was detected between any of the Wbl proteins and the only alternative sigma factors, σ^B, σ^H, or σ^J. The interaction between σ^A and WhiB1 or WhiB2 was disrupted in a heterologous system under growth conditions that produce nitric oxide and the iron-sulfur clusters of the isolated WhiB1 and WhiB2 proteins reacted with nitric oxide. Thus, K. sedentarius strain exhibits the major phenotypic characteristics of the type strain and a comprehensive examination of the interactions between its four Wbl proteins and four sigma factors suggested that the Wbl proteins all operate through interaction with σ^A.