Molecular cloning and expression in Escherichia coli of the Bacillus licheniformis bacitracin synthetase 2 gene.

The structural genes for the entire bacitracin synthetase 2 (component II) and for a part of the putative bacitracin synthetase 3 (component III) from Bacillus licheniformis ATCC 10716 were cloned and expressed in Escherichia coli. A cosmid library of B. licheniformis DNA was constructed. The library was screened for the ability to produce bacitracin synthetase by in situ immunoassay using anti-bacitracin synthetase antiserum. A positive clone designated B-15, which has a recombinant plasmid carrying about a 32-kilobase insert of B. licheniformis DNA, was further characterized. Analysis of crude cell extract from B-15 by polyacrylamide gel electrophoresis and Western blotting (immunoblotting) showed that the extract contains two immunoreactant proteins with high molecular weight. One band with a molecular weight of about 240,000 comigrates with bacitracin synthetase 2; the other band is a protein with a molecular weight of about 300,000. Partial purification of the gene products encoded by the recombinant plasmid by gel filtration and hydroxyapatite column chromatography revealed that one gene product catalyzes L-lysine- and L-ornithine-dependent ATP-PPi exchange reactions which are characteristic of bacitracin synthetase 2, and the other product catalyzes L-isoleucine-, L-leucine, L-valine-, and L-histidine-dependent ATP-PPi exchange activities, suggesting the activities of a part of bacitracin synthetase 3. Subcloning experiments indicated that the structural gene for bacitracin synthetase 2 is located near the middle of the insert.     

Effect of bacitracin on the sporulation of Bacillus licheniformis 28 KA

The bacitracin effect on spore germination in Bacillus licheniformis 28 KA--the producer of this antibiotic on media of various composition has been studied. Different intensity of antibiotic synthesis has been revealed on various media. A high content of presynthesized bacitracin has an inhibitory effect on spore germination in B. licheniformis.     

Isolation and characterization of Tn917-generated bacitracin deficient mutants of Bacillus licheniformis

Abstract Two Tn917-generated bacitracin deficient mutants of Bacillus licheniformis were isolated. Southern blot analysis of chromosomal DNA extracted from both insertional mutants showed that Tn917 inserted in the vicinity of the gene coding for the enzyme BA2 of the bacitracin synthetase enzyme complex. Measurements of bacitracin synthetase activity in cell-free extracts and positive hybridization signals in the vicinity of the BA2 gene indicate that in both bacitracin deficient mutants Tn917 could be inserted in the BA1 gene or in segments involved in regulation. Thus, it could be possible that the genes for bacitracin synthetase are clustered in the B. licheniformis genome.     

A nuclear magnetic resonance study of the metal binding sites in bacitracin.

Carbon-13 nuclear magnetic resonance spectroscopy has been used to identify sites in bacitracin which bind Cu2+ and Mn2+. Results are presented which implicate the free carboxyl groups of the aspartic and glutamic acid residues and the imidazole ring of the histidine residue as metal complexation sites between pH 6 and 8. Evidence is presented which also indicates that the thiazoline ring of bacitracin binds Mn2+. Bacitracin does not bind Cu2+ or Mn2+ at pH values of 2.5 or less.     

Sporulation of a bacitracin-sensitive mutant of Bacillus licheniformis is self-inhibited by bacitracin

A mutant of Bacillus licheniformis (BLU166) sensitive to its own antibiotic bacitracin was isolated and the mutation bcr-l was mapped close to the bacitracin synthetase genes. The sensitivity was shown to be specific for bacitracin. Two further bacitracin-sensitive strains were constructed, one (BLU171) with normal ability to synthesize bacitracin, and one (BLU170) a bacitracin non-producer. In addition to an increased sensitivity of growing cells to bacitracin, sporulation of the mutant strain BLU171 was self-inhibited by bacitracin. It is concluded that (1) there might exist at least two levels of resistance to bacitracin; (2) mutation bcr-1 affects a 'structural' component, which may protect the sensitive reaction of cell-wall biosynthesis; (3) sporulation is affected to a greater extent by bacitracin than vegetative growth; and (4) synthesis of bacitracin is independent of the presence of this resistance mechanism since the sensitive mutant produces similar amounts of the antibiotic to the wild-type strain.     

代谢工程改造L-半胱氨酸供给模块促地衣芽胞杆菌高效合成杆菌肽

杆菌肽是一种主要由芽胞杆菌产生的广谱性抗生素,目前作为兽药广泛应用于畜禽养殖领域.前体氨基酸供应不足可能是限制微生物发酵高产杆菌肽的重要因素.文中以杆菌肽工业生产菌株——地衣芽胞杆菌Bacillus licheniformis DW2为出发菌株,研究L-半胱氨酸供给模块强化对杆菌肽合成的影响.首先,构建了L-半胱氨酸合...     

Amino acid control mechanism for bacitracin formation byBacillus licheniformis

Several amino acids affected the amount of bacitracin produced by Bacillus licheniformis ATCC 10716 and the high-yielding mutant B. licheniformis AL. The possibility of an amino acid control mechanism for bacitracin biosynthesis is discussed. The two strains showed a different response to the addition of some amino acids. This indicate that they may have differences in their amino acid control mechanism.     

The role of the bacitracin ABC transporter in bacitracin resistance and collateral detergent sensitivity

The bacitracin resistance of Bacillus licheniformis, a producer of bacitracin, is mediated by the ABC transporter Bcr. Bacillus subtilis cells carrying bcr genes on high-copy number plasmids developed collateral detergent sensitivity, as did human cells with overexpressed multidrug resistance P-glycoprotein. Resistance against bacitracin and sensitivity of resistant cells to detergents were shown to be inseparable phenomena associated with the membrane part of Bcr transporter, namely protein BcrC. A fused protein, consisting of ATP-binding protein BcrA and membrane component BcrC was constructed. It resembled a half molecule of P-glycoprotein and was capable of providing a significant degree of antibiotic resistance and detergent sensitivity.     

Resistance to Bacitracin as Modulated by an Escherichia coli Homologue of the Bacitracin ABC Transporter BcrC Subunit from Bacillus licheniformis

A small open reading frame from the Escherichia coli chromosome, bcrC(EC), encodes a homologue to the BcrC subunit of the bacitracin permease from Bacillus licheniformis. We show that disruption of the chromosomal bcrC(EC) gene causes bacitracin sensitivity and, conversely, that BcrC(EC) confers bacitracin resistance when expressed from a multicopy plasmid.     

Changes in the level of bacitracin synthesis in autolysin-resistant strains of Bacillus licheniformis

Production of bacitracin by Bac. licheniformis 1001 and its spontaneous autolysin resistant variants was studied. It was found that the antibiotic activity of some variants was 1.5--2 times higher than that of the initial strain. No differences in the activity of serine exoprotease in the initial strain and resistant variants were observed. The latter variants lost their resistance to autolysis in 2--3 subcultures on solid and liquid nutrient media. their antibiotic activity in these cases decreased to the control level. The study indicates that there is a phenomenologic relation between the autolytic and antibiotic activities of Bac. licheniformis. The nature of the relation is not known yet. Possibly, it is due to changes in the specific metabolic steps connected with regulation of bacitracin synthesis.     

Sporulation in Bacillus licheniformis during altered bacitracin synthesis

Sporulation in different strains of Bacillus licheniformis, 10716 and 1001 in connection with changes in synthesis of bacitracin was studied. It was shown that the sporulation efficiency did not depend on the synthesis of the antibiotic: in some strains with low potency for the antibiotic production, the sporulation level was lowered, while in the others, it was not lowered. Moreover, normal sporulation was also observed, when the synthesis of bacitracin was inhibited. Therefore, it is suggested that there is no correlation between the sporulation and antibiotic production.     

Metal binding and structure-activity relationship of the metalloantibiotic peptide bacitracin

Bacitracin is a widely used metallopeptide antibiotic produced by Bacillus subtilis and Bacillus licheniformis with a potent bactericidal activity directed primarily against Gram-positive organisms. This antibiotic requires a divalent metal ion such as Zn(2+) for its biological activity, and has been reported to bind several other transition metal ions, including Mn(2+), Co(2+), Ni(2+), and Cu(2+). Despite the widespread use of bacitracin since its discovery in the early 1940s, the structure-activity relationship of this drug has not been established and the coordination chemistry of its metal complexes was not fully determined until recently. This antibiotic has been suggested to influence cell functioning through more than one route. Since bacterial resistance against bacitracin is still rare despite several decades of widespread use, this antibiotic can serve as an ideal lead for the design of potent peptidyl antibiotics lacking bacterial resistance. In this review, the results of physical (including NMR, EPR, and EXAFS) and molecular biological studies regarding the synthesis and structure of bacitracin, the coordination chemistry of its metal derivatives, the mechanism of its antibiotic actions, its influence on membrane function, and its structure and function relationship are discussed.     

Cloning of the genes controlling the biosynthesis of bacitracin in Bacillus licheniformis

The DNA fragment from bacitracin-producing Bacillus licheniformis strain is cloned on pMX39 vector plasmid in Bacillus subtilis cells. Bacillus subtilis cells carrying the cloned fragment inhibit the growth of bacitracin-sensitive tester strain. The observed inhibition of growth is due to the production by Bacillus subtilis of bacteriocin substance that is identified as bacitracin by TLC-chromatography. In contrast to the data published earlier it is shown that Bacillus subtilis can in fact produce the small amounts of bacitracin. Introduction of the cloned Bacillus licheniformis DNA into Bacillus subtilis cells stimulates this bacitracin production. The restriction site map of the Bacillus licheniformis chromosomal region bearing the cloned fragment is constructed.     

Proton NMR studies of Co(II) complexes of the peptide antibiotic bacitracin and analogues: insight into structure-activity relationship

Bacitracin is a widely used metal-dependent peptide antibiotic produced by Bacillus subtilis and Bacillus licheniformis with a potent bactericidal activity directed primarily against Gram-positive organisms. This antibiotic requires a divalent metal ion such as Zn(II) for its biological activity, and has been reported to bind several other transition metal ions, including Co(II), Ni(II), and Cu(II). Despite the wide use of bacitracin, a structure-activity relationship for this drug has not been established, and the structure of its metal complexes has not been fully determined. We report here one- and two-dimensional nuclear magnetic resonance (NMR) studies of the structure of the metal complexes of several bacitracin analogues by the use of paramagnetic Co(II) as a probe. The Co(II) complex of this antibiotic exhibits many well-resolved isotropically shifted (1)H NMR signals in a large spectral window ( approximately 200 ppm) due to protons near the metal, resulting from both contact and dipolar shift mechanisms. The assignment of the isotropically shifted (1)H NMR features concludes that bacitracin A(1), the most potent component of the bacitracin mixture, binds to Co(II) via the His-10 imidazole ring N(epsilon), the thiazoline nitrogen, and the monodentate Glu-4 carboxylate to form a labile complex in aqueous solutions. The free amine of Ile-1 does not bind Co(II). Several different analogues of bacitracin have also been isolated or prepared, and the studies of their Co(II) binding properties further indicate that the antimicrobial activity of these derivatives correlates directly to their metal binding mode. For example, the isotropically shifted (1)H NMR spectral features of the high-potent bacitracin analogues, including bacitracins A(1), B(1), and B(2), are virtually identical. However, Glu-4 and/or the thiazoline ring does not bind Co(II) in the bacitracin analogues with low antibiotic activities, including bacitracins A(2) and F.     

Engineered biosynthesis of the peptide antibiotic bacitracin in the surrogate host Bacillus subtilis.

Nonribosomal peptides are processed on multifunctional enzymes called nonribosomal peptide synthetases (NRPSs), whose modular multidomain arrangement allowed the rational design of new peptide products. However, the lack of natural competence and efficient transformation methods for most of nonribosomal peptide producer strains prevented the in vivo manipulation of these biosynthetic gene clusters. In this study, we present methods for the construction of a genetically engineered Bacillus subtilis surrogate host for the integration and heterologous expression of foreign NRPS genes. In the B. subtilis surrogate host, we deleted the resident 26-kilobase srfA gene cluster encoding the surfactin synthetases and subsequently used the same chromosomal location for integration of the entire 49-kilobase bacitracin biosynthetic gene cluster from Bacillus licheniformis by a stepwise homologous recombination method. Synthesis of the branched cyclic peptide antibiotic bacitracin in the engineered B. subtilis strain was achieved at high level, indicating a functional production and proper posttranslational modification of the bacitracin synthetases BacABC, as well as the expression of the associated bacitracin self-resistance genes. This engineered and genetically amenable B. subtilis strain will facilitate the rational design of new bacitracin derivatives.     

The two-component regulatory system BacRS is associated with bacitracin 'self-resistance' of Bacillus licheniformis ATCC 10716.

Bacitracin is a peptide antibiotic produced by several Bacillus licheniformis strains that is most active against other Gram-positive microorganisms, but not against the producer strain itself. Recently, heterologous expression of the bacitracin resistance mediating BcrABC transporter in Bacillus subtilis and Escherichia coli was described. In this study we could determine that the transporter encoding bcrABC genes are localized about 3 kb downstream of the 44-kb bacitracin biosynthetic operon bacABC. Between the bac operon and the bcrABC genes two orfs, designated bacR and bacS, were identified. They code for proteins with high homology to regulator and sensor proteins of two-component systems. A disruption mutant of the bacRS genes was constructed. While the mutant displayed no effects on the bacitracin production it exhibited highly increased bacitracin sensitivity compared to the wild-type strain. Western blot analysis of the expression of BcrA, the ATP-binding cassette of the transporter, showed in the wild-type a moderate BcrA induction in late stationary cells that accumulate bacitracin, whereas in the bacRS mutant cells the BcrA expression was constitutive. A comparison of bacitracin stressed and nonstressed wild-type cells in Western blot analysis revealed increasing amounts of BcrA and a decrease in BacR in the stressed cells. From these findings we infer that BacR acts as a negative regulator for controlling the expression of the bcrABC transporter genes.     

Enhancement of bacitracin biosynthesis by branched-chain amino acids in a regulatory mutant ofBacillus licheniformis

DL-4-Azaleucine-resistant mutant of Bacillus licheniformis azlr-1 isolated after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis, was a better bacitracin producer than the parent strain. In the minimal medium, the antibiotic biosynthesis was 4 times higher in the mutant than in the parent strain and less dependent on L-leucine addition. In the complex fermentation medium, the yield was 18-20% higher in the mutant strain. Transaminase B activity measured in the crude extract revealed that the branched-chain amino acid biosynthetic enzymes were 5-10 times derepressed supplying bacitracin synthetase with enhanced quantity of isoleucine and leucine, the building units of bacitracin molecule.     

Genetic mapping of the bacitracin synthetase gene(s) in Bacillus licheniformis

The map position of a mutation in the bacitracin synthetase gene(s) in Bacillus licheniformis ATCC 10716 was determined by transduction with phage SP-15. Results indicate that it is linked to the lys and trp loci and is distinct from the known sporulation loci on the chromosome of Bacillus licheniformis. The defect(s) of the enzyme complex were analysed in terms of its ability to bind covalently 14C-labelled amino acid precursors of the bacitracin molecule.     

Enzyme-bound intermediates in the biosynthesis of bacitracin.

1. Bacitracin synthetase, a three-component enzyme complex which catalyzes synthesis of the dodecapeptide bacitracin A, has been prepared from Bacillus licheniformis strains ATCC 10716, AL and SB 319. During synthesis of bacitracin, the amino acids (smaller amounts) and peptides are covalently bound to the enzyme complex. The nature of the bindings suggest that the amino acids and peptides are thioester linked. 2. The peptides, identified by thin-layer chromatography after performic acid liberation were Ile-Cys, Ile-Cys-Leu, Ile-Cys-Leu-Glu, Ile-Cys-Leu-Glu, Ile-Cys-Leu-Glu-Ile, Ile-Cys-Leu-Glu-Ile-Lys-Orn, Ile-Cys-Leu-Glu-Ile-Ile-Orn-Ile, Ile-Cys-L-EU-Glu-Ile-Lys-Orn-Ile-Phe, Ile-Cys-Leu-Glu-Ile-L-YS-Orn-Ile-Phe-His-Phe-His and Ile-Cys-Leu-Glu-Ile-Lys-Orn-Ile-Phe-His-Asp. 3. The labelled peptides covalently bound to bacitracin synthetase were intermediates in bacitracin synthesis. 4. Chain growth is initiated on one enzyme component (A) by the addition of isoleucine and cysteine. The sequential addition of the other amino acids proceeds in the C-terminal direction until the pentapeptide is formed. Further addition of amino acids and production of bacitracin are obtained by adding the other enzyme components (B and C) to the incubation mixture.