EXTRACELLULAR RIBONUCLEASE FORMATION IN BACILLUS SUBTILIS AND ITS STIMULATION BY ACTINOMYCIN D

Microbial ribonucleases (RNases): production and application potential

Ribonuclease (RNase) is hydrolytic enzyme that catalyzes the cleavage of phosphodiester bonds in RNA. RNases play an important role in the metabolism of cellular RNAs, such as mRNA and rRNA or tRNA maturation. Besides their cellular roles, RNases possess biological activity, cell stimulating properties, cytotoxicity and genotoxicity. Cytotoxic effect of particular microbial RNases was comparable to that of animal derived counterparts. In this respect, microbial RNases have a therapeutic potential as anti-tumor drugs. The significant development of DNA vaccines and the progress of gene therapy trials increased the need for RNases in downstream processes. In addition, RNases are used in different fields, such as food industry for single cell protein preparations, and in some molecular biological studies for the synthesis of specific nucleotides, identifying RNA metabolism and the relationship between protein structure and function. In some cases, the use of bovine or other animal-derived RNases have increased the difficulties due to the safety and regulatory issues. Microbial RNases have promising potential mainly for pharmaceutical purposes as well as downstream processing. Therefore, an effort has been given to determination of optimum fermentation conditions to maximize RNase production from different bacterial and fungal producers. Also immobilization or strain development experiments have been carried out.

Physiological responses of bacteria to cytochalasin A: effects on growth, transport, and enzyme induction

Cytochalasin A at 5 to 25 microgram/ml (1.0 x 10(-5) to 5.2 x 10(-5) M) inhibited the growth of three gram-positive bacteria, Arthrobacter sialophilus, Staphyloccus aureus, and Bacillus amyloliquifaciens, but had little or no effect on the growth of three gram-negative bacteria, Excherichia coli, Pseudomonas maltophilia, and Aeromonas proteolytica. A. sialophilus and S. aureus recovered spontaneously from cytochalasin A-mediated growth inhibition after a considerable lag period, which was dependent on the drug dose. It was demonstrated that this long-term recovery did not involve selection of resistant variants. Cytochalasin A had no detrimental effect on cell viability in A. sialophilus or S. aureus, but caused lysis of B. amyloliquifaciens. The drug prevented enzyme inductions and inhibited transport of valine, uridine, and glucose in the gram-positive organisms. It had little or no effect on these processes in the gram-negative organisms. In studies with A. sialophilus, the drug inhbitied respiration of exogenous substrates, but did not depress endogenous respiration. These results constitute the first unequivocal evidence for the bacteriostatic properties of this class of compounds and indicate that cytochalasin A halts various physiological processes in gram-positive bacteria primarily by inhibiting solute transport.

Membrane phospholipid asymmetry in Bacillus amyloliquefaciens

The phospholipid distribution in the membrane of Bacillus amyloliquefaciens was studied by using phospholipase C (B. cereus), phospholipase A2 (Crotalus), and the nonpenetrating chemical probe trinitrobenzenesulfonic acid. After treatment of intact protoplasts of B. amyloliquefaciens with either phospholipase, about 70% of total membrane phospholipid was hydrolyzed; specifically, about 90, 90, and 30% of phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin, respectively. Under these conditions, protoplasts remained intact and sealed. However, when protoplasts that were permeabilized by cold-shock treatment were incubated with either of the phospholipases, up to 80% of cardiolipin was hydrolyzed and phosphatidylglycerol and phosphatidylethanolamine were hydrolyzed virtually to completion. In intact cells, 92% of the phosphatidylethanolamine could be labeled with trinitrobenzenesulfonic acid under conditions in which the reagent did not penetrate the membrane to any significant extent. These results indicate that 70% of total phospholipid of this bacillus exists in the outer half of the bilayer. The distribution of phosphatidylethanolamine in this bilayer is highly asymmetric with it being located predominantly in the outer half. The results with phospholipases suggest that the distributions of cardiolipin and phosphatidylglycerol are also asymmetric but independent confirmation of this is required.

Effect of brefeldin A and actinomycin D on culture growth and brefeldin A yield in Curvularia lunata

Cultures incorporated with increasing quantities of brefeldin A in the form of crude extracts of fungal metabolites prior to inoculation demonstrated reduced growth rate and no significant increase in brefeldin A content. On the other hand, cultures incubated with increasing levels of actinomycin D on the 8th day of cultivation showed slight stimulation of brefeldin A formation with insignificant effect on growth.

Comparison of the patterns of increased in alpha-toxin and total extracellular protein by Staphylococcus aureus (Wood 46) grown in media supporting widely differing growth characteristics

A comparison has been made of total exoprotein formation by Staphylococcus aureus (Wood 46) in a tryptone soya broth (TSB) medium and a casein hydrolysate-yeast extract-containing (CCY) medium in which exponential growth occurred with doubling times of 3.0 and 1.3 h, respectively. It was found that the differential rate of exoprotein formation was biphasic in each case, increasing after the cessation of exponential growth by a factor of 4 in TSB and 7 in CCY medium. Although this relative change was greater in CCY medium, the maximum value of the differential rate was less than 40% of that achieved in TSB medium. It was further shown that throughout the growth cycle, and in both cultures, alpha-toxin accounted for the same proportion of total extracellular protein.

Relationship between exoprotease secretion and the synthesis of ribonucleic acid and protein in Bacillus amyloliquefaciens

Studies with washed bacteria suspended in fresh medium, in which bacterial densities were altered by a factor of four so as to cause accelerated entry of exponential bacteria into the postexponential phase and to re-establish growth in postexponential bacteria, have been performed. Under all the conditions examined rifampin, at a concentration of 0.5 mug/ml, inhibited [(14)C]uracil incorporation into total ribonucleic acid (RNA) by 90 to 95%. The percentage of inhibition of incorporation of (14)C-labeled amino acids into total protein achieved in parallel experiments was less, being not more than 80%. These results suggested that non-translatable RNA synthesis was inhibited more than messenger RNA (mRNA) by the antibiotic. It was found that on slowing the growth of exponential-phase bacteria exoprotease was formed at a high rate without a lag. It was further observed that when postexponential bacteria were induced to grow, by resuspending them at a lower density, exoprotease mRNA synthesis was switched off. The only synthesis of exoprotease which occurred in this case was accountable to pre-existing mRNA during its decay. Exoenzyme formation was found to be less susceptible to rifampin than total protein synthesis.

Effect of boseimycin on some enzyme systems of Bacillus subtilis

The effect of boseimycin on the in vitro activity and in vivo synthesis of alkaline phosphatase, aconitase and lactate, isocitrate, glutamate and alanine dehydrogenases was studied in Bacillus subtilis. At a subinhibitory concentration, synthesis of glutamate dehydrogenase was stimulated but alkaline phosphatase, lactate dehydrogenase and aconitase synthesis was inhibited. On the contrary, boseimycin inhibited slightly the activity of lactate dehydrogenase in cell-free extracts. Glutamate dehydrogenase and aconitase activities were not affected.

A study of the nature of the immediate precursor of the extracellular -amylase of Bacillus amyloliquefaciens. A reappraisal

1. A defined medium was devised for use in washed-cell experiments with post-exponential-phase cultures of Bacillus amyloliquefaciens. The medium allowed alpha-amylase to be secreted, bacterial concentration to increase and l-[U-(14)C]valine to be incorporated into protein at a linear rate, which was the same as in a post-exponential-phase culture, for up to 6h. 2. Determination of the specific radioactivity of l-[U-(14)C]valine in the medium, the intracellular amino acid pool, the cellular protein and the isolated alpha-amylase, after a 3h incubation of washed cells in the defined medium, showed that at least 76% of the alpha-amylase secreted was synthesized de novo. 3. By isolating the alpha-amylase formed during a 6h incubation in the presence of l-[U-(14)C]valine it was shown that the specific radioactivity of the N-terminal valine, within the limits of experimental error, was the same as that of the total valine residues from the complete alpha-amylase molecule. 4. A consideration of these results in relation to the whole literature on the subject strongly supports the idea that there is no reason to suppose that extracellular alpha-amylase is formed from a high-molecular-weight precursor in B. amyloliquefaciens and closely related organisms with identical characteristics of exoenzyme secretion.

Regulation of staphylococcal enterotoxin B

Several factors influenced the formation of enterotoxin B by Staphylococcus aureus strain S-6. In the standard casein hydrolysate medium, toxin was not produced in detectable quantities during exponential growth; it was produced during the post-exponential phase when total protein synthesis was arithmetic. The rate of toxin synthesis was much greater than the rate of total protein synthesis. The appearance of enterotoxin was inhibited by chloramphenicol; thus, the presence of toxin was dependent on de novo protein synthesis. When low concentrations of glucose (<0.30%) were added to the casein hydrolysate medium, growth was diauxic; glucose was completely metabolized during the first growth period. During the second growth period, enterotoxin was synthesized. In unbuffered casein hydrolysate medium containing excess glucose, toxin synthesis was completely repressed. The absence of toxin production under such conditions might be explained by the low (4.6) pH resulting from the acid end products of glucose metabolism. At pH <5.0, little or no toxin was produced. Toxin synthesis was initiated in the presence of glucose when the medium were buffered at any pH above 5.6. In such media, the differential rates of toxin synthesis, with respect to the rates of total protein synthesis, were lower than the differential rates in casein hydrolysate medium alone. Addition of glucose to a culture synthesizing toxin resulted in an immediate decrease in the differential rate without any change in pH. Thus, toxin synthesis appeared to be regulated by catabolite repression.

Effect of streptomycin on some enzyme systems of Bacillus subtilis

Streptomycin slightly inhibited lactic and malic dehydrogenases of Bacillus subtilis, and inhibited isocitric dehydrogenase to about 60%. The formation of lactic dehydrogenase, glutamic dehydrogenase, alpha-alanine dehydrogenase, and succinic dehydrogenase was stimulated by the antibiotic at a concentration causing 50% inhibition of bacterial growth. Streptomycin had practically no influence on the formation of malic dehydrogenase, but the antibiotic produced 48% inhibition of the synthesis of isocitric dehydrogenase.

Flagellar synthesis in Salmonella typhimurium: requirement for ribonucleic acid synthesis

The micro-complement-fixation assay has been demonstrated to be a sensitive assay for flagella which occur in nanogram amounts. By use of this assay, it was found that flagellar synthesis occurs during starvation of Salmonella typhimurium for tryptophan, an amino acid not present in flagellar protein. Under these conditions net ribonucleic acid (RNA) synthesis was reduced to approximately 10% of the control rate. Less than 1 mug of actinomycin D per ml further reduced RNA synthesis to less than 1% of the control rate in a culture sensitized by prior treatment for 5 min at 37 C with 5 x 10(-4)m ethylenediaminetetraacetate in 0.33 m tris(hydroxymethyl)aminomethane-chloride (pH 8.0). In the presence of actinomycin D, no synthesis of flagellar protein could be detected. Analysis of fractions of RNA separated by zone centrifugation indicated that actinomycin D reduces the production of template RNA as well as of ribosomal RNA. This suggests that in S. typhimurium the production of flagellar protein requires the concomitant synthesis of RNA. There is no evidence that a stable messenger RNA specific for flagellar synthesis is present.