ADP-ribosylation of proteins in Bacillus subtilis and its possible importance in sporulation

Endogenous ADP-ribosylation was detected in Bacillus subtilis, as determined in vitro with crude cellular extracts. The ADP-ribosylated protein profile changed during growth in sporulation medium, displaying a temporary appearance of two ADP-ribosylated proteins (36 and 58 kDa) shortly after the end of exponential growth. Mutants resistant to 3-methoxybenzamide, a known inhibitor of ADP-ribosyltransferase, were obtained, and a significant proportion (15%) were found to be defective in both sporulation and antibiotic production. These mutants failed to ADP-ribosylate the 36- and 58-kDa proteins. The parent strain also lost the ability to ADP-ribosylate these proteins when grown in the presence of 3-methoxybenzamide at a concentration at which sporulation but not cell growth was severely inhibited. Results from genetic transformations showed that the mutation conferring resistance to 3-methoxybenzamide, named brgA, was cotransformed with the altered phenotypes, i.e., defects in ADP-ribosylation and sporulation. spo0A and spo0F mutants displayed an ADP-ribosylation profile similar to that of the parent strain, but a spo0H mutant failed to ADP-ribosylate any proteins, including the 36- and 58-kDa proteins. The significance of protein ADP-ribosylation in sporulation was further indicated by the observation that ADP-ribosylation of the 36-kDa protein could be induced by treatment with decoyinine, an inhibitor of GMP-synthetase, and by amino acid limitation, both of which resulted in an immediate decrease in GTP pool size eventually leading to massive sporulation. We propose that a new sporulation gene, which presumably controls sporulation via ADP-ribosylation of certain functional proteins, exists.