The katX gene of Bacillus subtilis is under dual control of σ ^B and σ ^F

Abstract

The gene katX, which encodes a catalase in Bacillus subtilis, is transcribed by Eσ^F in the pre-spore. This catalase is responsible for the resistance to hydrogen peroxide shown by germinating and outgrowing spores. We demonstrated that katX is also a σ^B-dependent general stress gene, since it is strongly induced by heat, salt and ethanol stress, as well as by energy depletion. The −10 and −35 sequences of the σ^B- and σ^F-dependent promoters of katX overlap, and the transcriptional start points used by Eσ^B and Eσ^F differ by only one nucleotide. Our results indicate that the level of KatX level in outgrowing spores depends mainly on Eσ^F, because sigB mutants show normal KatX activity in dormant and outgrowing spores. katX mutants also develop the non-specific resistance to oxidative stress that is typical of glucose-starved cells. Therefore, the physiological role of σ^B-dependent katX expression remains obscure. The results indicate an overlap between the σ^B regulon and the σ^F regulon, and the physiological implications of this overlap are discussed.