Sigma factors are initiation factors that promote the attachment of RNA polymerase (RNAP) to specific initiation sites and are then released. Sigma B is not essential for sporulation; rather it is required for maximal expression of ctc and csbA which are transcribed in the early stationary phase under conditions inimical to sporulation. May play a role in the ability of the bacterium to adapt to various stresses but is not essential for its survival under these conditions. Positively regulates expression of its own operon. The second most abundant sigma factor, it associates with RNAP core under all growth phases (PubMed:21710567). Interacts transiently with the RNAP core. By heat shock, salt stress, oxidative stress, glucose limitation, oxygen limitation and entry into stationary phase. Association with RNAP core increases during alcohol, NaOH, NaCl stress and during sporulation (at protein level) (PubMed:21710567). Belongs to the sigma-70 factor family. SigB subfamily.