Biosynthesis of gramicidin and tryocidine in the Dubos strain of Bacillus brevis. I. Experiments with growing cultures

Creating Robust Antimicrobial Materials with Sticky Tyrocidines

Modified antimicrobial and antifouling materials and surfaces can be used to limit the propagation of microorganisms on various surfaces and minimise the occurrence of infection, transfer, and spoilage. Increased demand for ‘green’ solutions for material treatment has pushed the focus towards to naturally produced antimicrobials. Tyrocidines, cyclo-decapeptides naturally produced by a soil bacterium Brevibacillus parabrevis, have a broad spectrum of activity against Gram-positive and Gram-negative bacteria, filamentous fungi, and yeasts. Continual losses in tyrocidine production highlighted the possible association of peptides to surfaces. It was found in this study that tyrocidines readily associates with many materials, with a selectivity towards polysaccharide-type materials, such as cellulose. Peptide-treated cellulose was found to remain active after exposure to a broad pH range, various temperatures, salt solutions, water washes, and organic solvents, with the sterilising activity only affected by 1% SDS and 70% acetonitrile. Furthermore, a comparison to other antimicrobial peptides showed the association between tyrocidines and cellulose to be unique in terms of antimicrobial activity. The robust association between the tyrocidines and various materials holds great promise in applications focused on preventing surface contamination and creating self-sterilising materials.

Improved Intestinal Mucus Permeation of Vancomycin via Incorporation Into Nanocarrier Containing Papain-Palmitate

The aim of this study was to improve intestinal mucus permeation of a peptide antibiotic via incorporation into papain-palmitate-modified self-emulsifying drug delivery systems (SEDDS) as nanocarrier. Vancomycin as a peptide antibiotic was lipidized by hydrophobic ion pair formation using sodium bis-2-ethylhexyl-sulphosuccinate before incorporation in SEDDS comprising Capmul MCM, propylenglycol, and Kolliphor EL (2:1:2). As mucolytic agent, 0.5% papain-palmitate was introduced in SEDDS formulation containing the vancomycin-sodium bis-2-ethylhexyl-sulphosuccinate ion pair. The formulation was evaluated regarding droplet size, zeta potential, and cytotoxicity using Caco-2 cells previous to intestinal mucus permeation studies using Transwell diffusion and rotating tube method. The hydrophobic ion pair product yielded from surfactant to drug ratio of 3:1 provided a 25-fold increase in lipophilicity, drug payload in SEDDS of 5%, and log D_{SEDDS/release medium} of 2.2. The formulation exhibited a droplet size and zeta potential of 221.5 ± 14.8 nm and -4.2 ± 0.8 mV, respectively. Cytotoxicity study showed that SEDDS formulations were not toxic. Introducing 0.5% papain-palmitate increased the mucus permeability of SEDDS 2.8-fold and 3.3-fold in Transwell diffusion and rotating tube studies, respectively. According to these results, papain decorated SEDDS might be a potential strategy to improve the mucus permeating properties of peptide antibiotics.

In vivo modification of native carrier protein domains

Carrier proteins are central to the biosynthesis of primary and secondary metabolites in all organisms. Here we describe metabolic labeling and manipulation of native acyl carrier proteins in both type I and II fatty acid synthases. By utilizing natural promiscuity in the CoA biosynthetic pathway in combination with synthetic pantetheine analogues, we demonstrate metabolic labeling of endogenous carrier proteins with reporter tags in Gram-positive and Gram-negative bacteria and in a human carcinoma cell line. The highly specific nature of the post-translational modification that was utilized for tagging allows for simple visualization of labeled carrier proteins, either by direct fluorescence imaging or after chemical conjugation to a fluorescent reporter. In addition, we demonstrate the utility of this approach for the isolation and enrichment of carrier proteins by affinity purification. Finally, we use these techniques to identify a carrier protein from an unsequenced organism, a finding that validates this proteomic approach to natural product biosynthetic enzyme discovery.

Biosynthesis of isotopically labeled gramicidins and tyrocidins by Bacillus brevis

The three-dimensional structure of bilayer-associated gramicidin A is available from a structural data base. This and related peptides are, therefore, ideal model compounds to use during the implementation and development of new NMR techniques for the structural investigations of membrane proteins. As these methods rely on the isotopic labelling of single, selected or all sites, we have, investigated and optimised biochemical protocols using different strains of the Gram-positive bacterium Bacillus brevis. With newly developed schemes for isotopic labelling large amounts of gramicidin and tyrocidin enriched with stable isotopes such as (15)N or (15)N/(13)C have been obtained at low cost. A variety of analytical and spectroscopic techniques, including HPLC, mass spectrometry and NMR spectroscopy are used to characterise the resulting products.

THE BIOSYNTHESIS OF GRAMICIDIN S IN A CELL-FREE SYSTEM

1. A cell-free system prepared from Bacillus brevis cells, harvested in the late phase of growth and consisting of the 11000g supernatant, has been shown to incorporate into gramicidin S the five constituent amino acids added in labelled form. The results are consistent with complete synthesis and not merely a completion of pre-existing intermediate peptides. 2. The incorporation of (14)C-labelled amino acids by the 11000g supernatant into gramicidin S requires an energy source. Omission of phosphoenolpyruvate and pyruvate kinase from the incubation mixture prevents incorporation into gramicidin S. The cell-free system incorporates [(14)C]-leucine, -proline and -phenylalanine over a period of 4hr. With [(14)C]leucine, incorporation into gramicidin S takes place in the range pH6-9 with maximum incorporation at pH7.0. High concentrations of chloramphenicol or puromycin decreased the incorporation into gramicidin S by only about 20%. 3. The 50000g supernatant exhibited no decrease in ability of incorporating [(14)C]valine into gramicidin S as compared with the 11000g supernatant. About 40% of the incorporating ability remained in the 105000g supernatant after 3hr. centrifugation. When recombining the 105000g sediment with the 105000g supernatant, some increase in incorporation over that obtained with the supernatant alone was obtained. The findings tend to support the view that gramicidin S is synthesized in a different manner from that of proteins.

Branched-chain amino acid substitutions in the biosynthesis of the antibiotic actinomycin

Actinomycins normally contain N-methyl-l-valine and either d-valine, d-alloisoleucine or both amino acids in the molecule. During antibiotic formation in a medium supplemented with one of the four isoleucine stereoisomers, Streptomyces parvulus and S. chrysomallus form complex actinomycin mixtures (C(1), C(2), C(3), E(1), and E(2)-like compounds). Although chromatographic techniques suggested that single homogeneous components had been isolated, subsequent studies indicated that such chromatographic fractions probably consisted of multiple isomers of actinomycin. Amino acid analyses revealed the presence of N-methylvaline and/or N-methylalloisoleucine and, in addition, d-isoleucine, d-valine, and d-alloisoleucine were frequently found in a given fraction.

The use of acid alumina and sephadex LH-20 for the separation and characterization of ethanol-soluble peptides produced by Bacillus brevis

Cell extracts from Bacillus brevis (A.T.C.C. 10068), grown with various media, incorporated certain (14)C-labelled amino acids that are normally components of tyrothricin into material that was extracted by ethanol from the precipitate formed by adding acid. When this material was separated by paper and silica-gel thin-layer chromatography and paper electrophoresis (14)C was located in those regions that also contained gramicidin and tyrocidine. From a study of the properties of the system responsible for the incorporation it was deduced that non-tyrothricin materials were present. It was shown that the methods normally used to characterize tyrothricin do not adequately distinguish between tyrothricin and non-tyrothricin materials. However, a method for separating these materials was devised. This involved elution with ethanol from columns of acid alumina followed by gel filtration on Sephadex LH-20 with dimethylformamide-water solvent. The behaviour of gramicidin and tyrocidine on the Sephadex LH-20 column was examined, and it was concluded that the separation was not caused simply by gel filtration of unassociated molecules. Also, tyrocidine molecules with different amino acid compositions seemed to have different affinities for the Sephadex LH-20 column.

Multiple forms of bacterial hydrogenases

Ackrell, B. A. C. (University of Hawaii, Honolulu), R. N. Asato, and H. F. Mower. Multiple forms of bacterial hydrogenases. J. Bacteriol. 92:828-838. 1966.-Extracts of certain bacterial species have been shown by disc electrophoresis on polyacrylamide gel to contain multiple hydrogenase systems. The hydrogenase enzymes comprising these systems have different electrophoretic mobilities and produce a band pattern that is unique for each bacterial species. Of 20 bacterial species known to possess hydrogenase activity and which were examined by this technique, only the activities of Clostridium tetanomorphum and C. thermosaccharolyticum could be attributed, at pH 8.3, to a single hydrogenase enzyme. This multiplicity of hydrogenase forms was found both in bacteria which contain mostly soluble hydrogenases and in those where the hydrogenase is predominantly associated with particulate material. When solubilization of this particulate material could be effected, at least two solubilized hydrogenases were released, and, of these, one would have the same electrophoretic properties (i.e., R(F)) as one of the soluble hydrogenases already present in small amounts within the cell. Different growth conditions for various types of bacteria, such as the nitrogen source, the degree of aeration, and photosynthetic versus aerobic growth in the dark, as well as the conditions under which the cells were stored, markedly affected the hydrogenase activity of the cells, but not their hydrogenase band pattern. The disc electrophoresis technique proved to be 10 times more sensitive than the manometric technique in detecting hydrogenase activity.