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.