Control of antibiotic biosynthesis

The glycerol utilization operon of Streptomyces coelicolor: genetic mapping of gyl mutations and the analysis of cloned gylDNA

Glycerol-3-phosphate dehydrogenase (gylB) mutations (which cause glycerol sensitivity), and presumed glycerol kinase (gylA) and/or regulatory mutations eliminating both glycerol-3-phosphate dehydrogenase and glycerol kinase activities, map close to the argA locus of Streptomyces coelicolor A3(2). Using the plasmid vector pIJ702 and restriction enzymes BglII and SstI, extensively overlapping S. coelicolor DNA fragments of 2.74 kb and 2.84 kb were isolated, either of which could restore the wild-type phenotype to gylB and some gylA mutants. Genetic and biochemical analyses of mutants carrying the cloned gyl DNA suggested that a functional gyl promoter had not been cloned, and that restoration of the Gyl+ phenotype was achieved by recombination between the cloned and chromosomal gyl DNA sequences. After subcloning parts of this DNA into the phage vector phi C31 KC400, "gene disruption" analysis was carried out, which confirmed the absence of the gyl promoter, and indicated that a polycistronic mRNA traverses gylA and then gylB.

Regulatory mutants of Streptomyces clavuligerus affected in free diaminopimelic acid content and antibiotic biosynthesis

The composition of intracellular free amino acid pools was determined in Streptomyces clavuligerus mutants possessing an altered aspartokinase which is insensitive to concerted feedback inhibition by threonine and lysine. These mutants contained total free amino acid pool contents that were considerably higher than those found in the wild-type strain. Diaminopimelic acid accounted for 10 to 20% of the total free amino acid pools, depending on the individual mutant and its culture growth phase, whereas diaminopimelic acid contained in the wild-type strain accounted for only 0.5% of the total free amino acid pool.

Effect of phosphate and amino acids on echinomycin biosynthesis by Streptomyces echinatus

Streptomyces echinatus produces only echinomycin (quinomycin A), in contrast to other streptomycetes, which produce families of quinoxaline antibiotics differing in the amino acid composition of the oligopeptide (quinomycins A, B, B0, C, D, and E) or the structure of the sulfur-containing cross bridge (triostins A, B, and C). Attempts were made to establish conditions for directed biosynthesis with S. echinatus. The lability of the peptide lactone to alkaline pH was obviated by using high levels of phosphate or HEPES [4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid] buffer in the production medium. Maintaining the pH below 7.5 resulted in an apparent stimulation of production. Amino acids which serve as structural components or as precursors of echinomycin were employed singly or in combination with nitrate in a chemically defined medium. Based on specific yield (micrograms of echinomycin per milligram of mycelia [dry weight]), D- and L-serine, D-alanine, L-valine, and L-phenylalanine produced equivalent yields of antibiotic which were approximately twofold greater than yields obtained with nitrate alone. In contrast, L-alanine, beta-alanine, and L-threonine produced a three- to fourfold stimulation of production. Although the other amino acids diminished antibiotic production, L-isoleucine, which ostensibly was inhibitory to production, supported the accumulation of a quinoxaline antibiotic in which the cross-bridge sulfur lacked a methyl group.

Bioreactors: Design and Operation

The bioreactor provides a central link between the starting feedstock and the product. The reaction yield and selectivity are determined by the biocatalyst, but productivity is often determined by the process technology; as a consequence, biochemical reaction engineering becomes the interface for the biologist and engineer. Developments in bioreactor design, including whole cell immobilization, immobilized enzymes, continuous reaction, and process control, will increasingly reflect the need for cross-disciplinary interaction in the biochemical process industry.

Regulation of hydrolase formation and phosphate release in turimycin fermentations

During the turimycin fermentation hydrolytic enzymes are excreted responsible for orthophosphate release from phosphate-containing dissolved and undissolved complex medium constituents. Following a phosphate-limited growth period the phosphate release leads to a second growth period (diauxic growth). Depending on the rate of phosphate release the length of the lag phase of diauxic growth changes in different fermentations. The resulting second growth period is correlated with a transient delay in the formation of turimycin, of phosphatases and of nucleases. The amylolytic activities are formed already within the first hours after the beginning of fermentations. Phosphatases, nucleases and protease are excreted parallel to turimycin formation after extracellular phosphate limitation in presence of ammonia and glucose. A special role of phosphate limitation initiating enzyme synthesis is proposed.

Production of Rosamicin: Improvement of Synthetic Medium

Rosamicin is one of the important macrolide antibiotics that has clinical efficacy and broad-spectrum antibacterial activity. Using a mutant strain of Micromonospora rosaria (NRRL 3718), a chemically defined medium was developed, and some fermentation conditions that are important to rosamicin biosynthesis were optimized to achieve rosamicin productivity of 230 μg/ml. Soluble starch and l -asparagine were found to be the best carbon and nitrogen sources, and a stimulative effect of magnesium and zinc ions was also found. The medium developed contains: soluble starch, 4%; l -asparagine, 0.15%; K 2 HPO 4 , 0.075%; CaCO 3 , 0.6%; MgSO 4 · 7H 2 O, 0.05%; FeSO 4 · 7H 2 O, 10 −4 M; CuSO 4 · 5H 2 O, 10 −5 M; ZnSO 4 · 7H 2 O, 10 −5 M; and MnSO 4 · (4-6)H 2 O, 10 −6 M. The required air supply was about 40 mmol of O 2 liter −1 · h −1 · atm −1 , and the favorable culture temperature was 28 to 29°C.

Chloramphenicol acetyltransferase: enzymology and molecular biology

Naturally occurring chloramphenicol resistance in bacteria is normally due to the presence of the antibiotic inactivating enzyme chloramphenicol acetyltransferase (CAT) which catalyzes the acetyl-S-CoA-dependent acetylation of chloramphenicol at the 3-hydroxyl group. The product 3-acetoxy chloramphenicol does not bind to bacterial ribosomes and is not an inhibitor of peptidyltransferase. The synthesis of CAT is constitutive in E. coli and other Gram-negative bacteria which harbor plasmids bearing the structural gene for the enzyme, whereas Gram-positive bacteria such as staphylococci and streptococci synthesize CAT only in the presence of chloramphenicol and related compounds, especially those with the same stereochemistry of the parent compound and which lack antibiotic activity and a site of acetylation (3-deoxychloramphenicol). Studies of the primary structures of CAT variants suggest a marked degree of heterogeneity but conservation of amino acid sequence at and near the putative active site. All CAT variants are tetramers composed in each case of identical polypeptide subunits consisting of approximately 220 amino acids. The catalytic mechanism does not appear to involve an acyl-enzyme intermediate although one or more cysteine residues are protected from thiol reeagents by substrates. A highly reactive histidine residue has been implicated in the catalytic mechanism.

Industrial microbiology

Industrial microbiology has served humanity since prebiblical times, providing fermented beverages and foods to enhance the quality of life. The antibiotic era featured an explosion in the number of microbial products for medicine, nutrition, industry, and research. Revolutionary developments in molecular genetics are propelling the field into a new growth phase with promise of solutions to major world problems.

Bacitracin and protease production in relation to sporulation during exponential growth of Bacillus licheniformis on poorly utilized carbon and nitrogen sources

Growth of Bacillus licheniformis in a chemically defined medium containing glucose and ammonium chloride yielded a doubling time of 1.00 h. Examination of the culture during exponential growth revealed a lack of heat-resistant spores together with a complete absence of detectable concentrations of bacitracin or extracellular serine protease. Replacement of glucose as the sole carbon source by glycerol, pyruvic acid, citric acid, or lactic acid resulted in doubling times of 1.13, 2.00, 3.16, and 3.95 h, respectively. Bacitracin, protease, and heat-resistant spores were produced during exponential growth in amounts related to these doubling times. A qualitatively similar pattern was observed when ammonium chloride was replaced by sodium nitrate, alanine, or glutamic acid which gave doubling times of 1.65, 1.77, and 1.90 h, respectively. Protease, but not bacitracin, concentrations were substantially higher when the growth rate was restricted by use of poor nitrogen rather than poor carbon sources. The relationships between bacitracin production, protease production, and the sporulation process are discussed.

6-Methylsalicylic Acid Production in Solid Cultures of Penicillium patulum Occurs Only When an Aerial Mycelium Is Present

When Penicillium patulum was grown on Czapek-Dox agar, 6-methylsalicylic acid was produced as an aerial mycelium was forming. Nutrients were often plentiful in the medium when biosynthesis began. If the formation of an aerial mycelium was prevented by growing the fungus between two sheets of dialysis membrane, no 6-methylsalicylic acid was produced even when nutrients were completely consumed. If the upper sheet of dialysis membrane was stripped off cultures of the latter type, an aerial mycelium formed; concomitantly, 6-methylsalicylic acid biosynthesis was observed. We conclude that 6-methylsalicylic acid was produced only by P. patulum colonies that possessed an aerial mycelium.