Alternative sigma factor σ(H )activates competence gene expression in Lactobacillus sakei

BACKGROUND: Alternative sigma factors trigger various adaptive responses. Lactobacillus sakei, a non-sporulating meat-borne bacterium, carries an alternative sigma factor seemingly orthologous to σ(H )of Bacillus subtilis, best known for its contribution to the initiation of a large starvation response ultimately leading to sporulation. As the role of σ(H)-like factors has been little studied in non-sporulating bacteria, we investigated the function of σ(H )in L. sakei. RESULTS: Transcription of sigH coding for σ(H )was hardly affected by entry into stationary phase in our laboratory conditions. Twenty-five genes potentially regulated by σ(H )in L. sakei 23 K were revealed by genome-wide transcriptomic profiling of sigH overexpression and/or quantitative PCR analysis. More than half of them are involved in the synthesis of a DNA uptake machinery linked to genetic competence, and in DNA metabolism; however, σ(H )overproduction did not allow detectable genetic transformation. σ(H )was found to be conserved in the L. sakei species. CONCLUSION: Our results are indicative of the existence of a genetic competence state activated by σ(H )in L. sakei, and sustain the hypothesis that σ(H)-like factors in non sporulating Firmicutes share this common function with the well-known ComX of naturally transformable streptococci.