Effect of purine and pyrimidine limitations on RNA synthesis in Bacillus subtilis.

The effects of varying the intracellular levels of GTP or UTP on the rate of RNA synthesis in Bacillus subtilis were studied. The levels of these nucleotides were manipulated by pyrimidine limitation in a pyr auxotroph, by purine limitation in a pur auxotroph, or by the addition of decoyinine , which specifically inhibits GMP synthesis. Decreased levels of UTP and GTP were accompanied by dramatically decreased synthesis and accumulation of stable RNAs (tRNA and rRNA), but mRNA synthesis was less affected. However, sporulation was initiated only when the intracellular level of GTP decreased.     

Regulation of polyglutamic acid synthesis by glutamate in Bacillus licheniformis and Bacillus subtilis

The synthesis of polyglutamic acid (PGA) was repressed by exogenous glutamate in strains of Bacillus licheniformis but not in strains of Bacillus subtilis, indicating a clear difference in the regulation of synthesis of capsular slime in these two species. Although extracellular gamma-glutamyltranspeptidase (GGT) activity was always present in PGA-producing cultures of B. licheniformis under various growth conditions, there was no correlation between the quantity of PGA and enzyme activity. Moreover, the synthesis of PGA in the absence of detectable GGT activity in B. subtilis S317 indicated that this enzyme was not involved in PGA biosynthesis in this bacterium. Glutamate repression of PGA biosynthesis may offer a simple means of preventing unwanted slime production in industrial fermentations using B. licheniformis.     

Regulation of synthesis of glutamine synthase in Bacillus subtilis

A study of the regulation of the synthesis of the enzyme glutamine synthase in Bacillus subtilis was initiated. An assay, based on the measurement of glutamo-hydroxamate, was used to characterize the enzyme in crude preparations and in toluene-treated cells. Determinations were made of the Michaelis constants for adenosine triphosphate, hydroxylamine, and glutamate (9 x 10(-3), 4 x 10(-3), and 2.2 x 10(-2)m, respectively), the pH optimum (7.6 to 7.7), and the stability. The differential rate of synthesis was determined under various growth conditions. The enzyme was found to be relatively insensitive to regulation. Partial repression was caused by glutamine, arginine, asparagine, and glutamate, or by carbon limitation in a chemostat. Derepression was caused by exhaustion of externally added amino acids or by nitrogen limitation in a chemostat.     

Catabolite-induced repression of sporulation in Bacillus subtilis

In response to nutrient limitations, Bacillus subtilis cells undergo a series of morphological and genetic changes that culminate in the formation of endospores. Conversely, excess catabolites inhibit sporulation. It has been demonstrated previously that excess catabolites caused a decrease in culture medium pH in a process that required functional AbrB. Culture medium acidification was also shown to inhibit sigmaH-dependent sporulation gene expression. The studies reported here investigate the effects of AbrB-mediated pH sensing on B. subtilis developmental competence. We have found that neither addition of a pH stabilizer, MOPS (pH 7.5), nor null mutations in abrB blocked catabolite repression of sporulation. Moreover, catabolite-induced culture medium acidification was observed in cultures of catabolite-resistant sporulation mutants, crsA47, rvtA11, and hpr-16, despite their efficient sporulation. These results suggest that AbrB-mediated pH sensing is not the only mechanism regulating catabolite repression of sporulation. The AbrB pathway may function to channel cells toward genetic competence, as opposed to other postexponential differentiation pathways.     

Partial nucleotide limitation induces phosphodiesterase I and 5'-nucleotidase in Bacillus subtilis.

Changes in the specific activity of enzymes involved in the degradation of RNA and nucleotides were measured in Bacillus subtilis under conditions of guanine deprivation, which initiates sporulation, and uracil deprivation, which does not initiate sporulation. Whereas the specific activities of most of the enzymes studied increased by less than a factor of 3, those of 5'-mononucleotide-producing phosphodiesterase and 5'-nucleotidase increased at least eightfold under both deprivation conditions.     

CcpA-independent carbon catabolite repression in Bacillus subtilis

The past decade has witnessed an exiting unveiling of numerous molecular mechanisms that characterize signal transduction by protein-protein interaction. The recent findings encouraged an increasing effort to understand the sequential metabolism of different sugars available as energy sources at the same time. It seems probable that at least three principle mechanisms which act together or separately, mediate carbon catabolite repression (CCR) depending on the system which is under metabolic control: i) by the main signal transducing chain via the ATP-dependent HPr-kinase, HPr(Ser46-P) or alternatively Crh via the central component CcpA and its interaction with cre, ii) by signals sensed from the specific regulators directly or via phosphorylation by HPr, iii) by inducer exclusion based on the concurrence of the enzyme IIA(Glc) domain of the glucose permease, and other PTS-dependent permeases composed only of the B and C domains and lacking the enzyme IIA domain.     

Regulation of glutamate dehydrogenase in Bacillus subtilis.

The activity of the nicotinamide adenine dinucleotide-dependent glutamate dehydrogenase in Bacillus subtilis was influenced by the carbon source, but not the nitrogen source, in the growth medium. The highest specific activity for this enzyme was found when B. subtilis was grown in a minimal or rich medium that contained glutamate as the carbon source. It is proposed that glutamate dehydrogenase serves a catabolic function in the metabolism of glutamate, is induced by glutamate, and is subject to catabolite repression.