Sigma factor and sporulation genes in Clostridium

Abstract

The genus Clostridium, represented by Gram-positive, anaerobic, spore-forming bacteria, is well known for its clinical importance and considerable biotechnological potential. Recently, evidence for a functional role of the transcription factors σ A, σ E, σ G, and σ K in this genus was provided by cloning and sequencing these genes from C. acetobutylicum. In C. kluyveri, a partially sequenced open reading frame was found to encode the N terminus of the putative σ factor L with significant similarity to members of the σ 54 family. The identification of sequences with high similarity to the Bacillus σ F ( C. acetobutylicum), σ H (several clostridial species), and σ D ( C. thermocellum)-controlled consensus promoters renders the existence of these transcription factors in clostridia very likely. These data are in agreement with information obtained by RNA transcript mapping ( σ A, σ H), heterologous DNA hybridization ( σ D, σ H), and immuno characterization of purified proteins ( σ A) from various clostridial species. Thus, the picture emerges that a fundamental similarity exists at the genetic level between the regulation of various cellular responses, in particular sporulation, in the genera Bacillus and Clostridium. The different induction patterns of sporulation in Bacillus spp. (nutrient starvation) and many clostridial species (cessation of growth or exposure to oxygen in the presence of excess nutrients) are most interestingly not reflected in the general regulatory features of this developmental process.