SIGMA-FACTOR AND SPORULATION GENES IN CLOSTRIDIUM

The genus Clostridium, represented by Gram-positive, anaerobic, spore- forming bacteria, is well known for its clinical importance and consid erable biotechnological potential. Recently, evidence for a functional role of the transcription factors sigma(A), sigma(E), sigma(G), and s igma(K) in this genus was provided by cloning and sequencing these gen es from C. acetobutylicum. In C. kluyveri, a partially sequenced open reading frame was found to encode the N terminus of the putative sigma factor L with significant similarity to members of the sigma(54) fami ly. The identification of sequences with high similarity to the Bacill us sigma(F) (C. acetobutylicum), sigma(H) (several clostridial species ), and sigma(D) (C. thermocellum)-controlled consensus promoters rende rs the existence of these transcription factors in clostridia very lik ely. These data are in agreement with information obtained by RNA tran script mapping (sigma(A), sigma(H)) heterologous DNA hybridization (si gma(D), sigma(H)), and immuno characterization of purified proteins (s igma(A)) from various clostridial species. Thus, the picture emerges t hat a fundamental similarity exists at the genetic level between the r egulation of various cellular responses, in particular sporulation, in the genera Bacillus and; Clostridium. The different induction pattern s of sporulation in Bacillus spp. (nutrient starvation) and many clost ridial species (cessation of growth or exposure to oxygen in the prese nce of excess nutrients) are most interestingly not reflected in the g eneral regulatory features of this developmental process.