Investigation of halogenation during the biosynthesis of ramoplanin in Actinoplanes sp. ATCC33076.

Ramoplanin and enduracidin are lipopeptide antibiotics effective against Gram-positive pathogens, which share close similarity in structure and biosynthetic pathway. Both compounds have chlorine atoms attached to 4-hydroxyphenylglycine (Hpg) but with different chlorinating sites and levels. Here, to probe the factor affecting the site and level of halogenation, gene inactivation and heterologous expression were carried out in Actinoplanes sp. ATCC33076 by homologous recombination. Metabolite analysis confirmed that ram20 encodes the only halogenase in ramoplanin biosynthetic pathway, and enduracidin halogenase End30 could heterologously complement the ram20-deficient mutant. Additionally, the mannosyltransferase-deficient mutant produces a dichlorinated ramoplanin aglycone with the halogenation site at Hpg(13). This study has refined our understanding of how halogenation occurs in ramoplanin biosynthetic pathway, and lays the foundation for further exploitation of ramoplanin and enduracidin halogenase in combinatorial biosynthesis.

Genetic manipulation revealing an unusual N-terminal region in a stand-alone non-ribosomal peptide synthetase involved in the biosynthesis of ramoplanins.

Ramoplanins produced by Actinoplanes are new structural class of lipopeptide and are currently in phase III clinical trials for the prevention of vancomycin-resistant enterococcal infections. The depsipeptide structures of ramoplanins are synthesized by non-ribosomal peptide synthetases (NRPS). Romo-orf17, a stand-alone NRPS, is responsible for the recruitment of Thr into the linear NRPS pathways for which the corresponding adenylation domain is absent. Here, systematical gene inactivation and complementation have been carried out in a Actinoplanes sp. using homologous recombination and site-specific integration methods. A hybrid gene coding for the N-terminal region of the stand-alone NRPS and the A-PCP domains of a heterologous NRPS restored production of ramoplanins. The results elucidate the unusual N-terminal region which is essential for the biosynthesis of ramoplanins.

Production of ramoplanin analogues by genetic engineering of Actinoplanes sp.

Ramoplanins are lipopeptides effective against a wide range of Gram-positive pathogens. Ramoplanin A2 is in Phase III clinical trials. The structure-activity relationship of the unique 2Z,4E-fatty acid side-chain of ramoplanins indicates a significant contribution to the antimicrobial activities but ramoplanin derivatives with longer 2Z,4E-fatty acid side-chains are not easy to obtain by semi-synthetic approaches. To construct a strain that produces such analogues, an acyl-CoA ligase gene in a ramoplanin-producing Actinoplanes was inactivated and a heterologous gene from an enduracidin producer (Streptomyces fungicidicus) was introduced into the mutant. The resulting strain produced three ramoplanin analogues with longer alkyl chains, in which X1 was purified. The MIC value of X1 was ~0.12 µg/ml against Entrococcus sp. and was also active against vancomycin-resistant Staphylococcus aureus (MIC = 2 µg/ml).

Functional identification of the gene encoding the enzyme involved in mannosylation in ramoplanin biosynthesis in Actinoplanes sp.

Ramoplanin is a lipopeptide antibiotic active against multi-drug-resistant, Gram-positive pathogens. Structurally, it contains a di-mannose moiety attached to the peptide core at Hpg(11). The biosynthetic gene cluster of ramoplanin has already been reported and the assembly of the depsipeptide has been elucidated but the mechanism of transferring sugar moiety to the peptide core remains unclear. Sequence analysis of the biosynthetic gene cluster indicated ramo-orf29 was a mannosyltransferase candidate. To investigate the involvement of ramo-orf29 in ramoplanin biosynthesis, gene inactivation and complementation have been conducted in Actinoplanes sp. ATCC 33076 by homologous recombination. Metabolite analysis revealed that the ramo-orf29 inactivated mutant produced no ramoplanin but the ramoplanin aglycone. Thus, ramo-orf29 codes for the mannosyltransferase in the ramoplanin biosynthesis pathway. This lays the foundation for further exploitation of the ramoplanin mannosyltransferase and aglycone in combinatorial biosynthesis.

[A new sesquiterpenoid from fungus Colletotrichum sp. and its cytotoxicity].

A novel sesquiterpenoid (1) and three known compounds identified as isoaltenuene (2), altenuene (3), and alternariol 4, 10-O-dimethyl ether (4), were isolated in our investigation of the cytotoxic constituents from solid cultures of the endophytic fungus Colletotrichum sp. The structures of these compounds were elucidated through spectroscopic data analysis. All compounds exhibited cytotoxic activity against lung cancer cell line A549, breast cancer cell line MDA-MB-231 and pancreatic cancer cell line PANC-1. Compound 4 could induce the PANC-1 cells inflation or death, but couldn't induce apoptosis at the IC50 of 60.2 microg x mL(-1).

An efficient and novel screening model for assessing the bioactivity of extracts against multidrug-resistant Pseudomonas aeruginosa using Caenorhabditis elegans.

As a large number of multidrug-resistant bacteria have emerged, and there is an urgent need for the development of new antibacterial agents. In this study, we developed a liquid-based slow killing assay to be carried out in standard 96-well microtiter plates. This screening method was designed to facilitate high-throughput screening of small molecules and extracts. In antibiotic rescue assays, the Caenorhabditis elegans multidrug-resistant Pseudomonas aeruginosa infection model displayed a high degree of drug resistance in vivo and in vitro. We used the method to screen 1,300 extracts, and found 36 extracts (2.7%) which prolonged the survival of infected nematodes, and four (0.3%) of these extracts showed in vitro and in vivo anti-multidrug resistant P. aeruginosa activity. These results indicate that the whole-animal C. elegans multidrug-resistant bacterial model can be used to screen antibacterial compounds, and can also be useful for bioactive compounds which most likely cannot be identified in vitro.

Improvement of spinosad production by overexpression of gtt and gdh controlled by promoter PermE* in Saccharopolyspora spinosa SIPI-A2090.

Spinosyns A and D are novel macrolide secondary metabolites containing two deoxysugars. Each of the sugars is derived from a common intermediate, which is biosynthesized sequentially by NDP-glucose synthase and glucose dehydratase. Systematical duplication of gtt and gdh was carried out by genetic engineering in Saccharopolyspora spinosa. Introduction of additional gtt and gdh genes under the control of PermE* promoter showed significant increase on their transcript levels. The production of spinosad was increased by over threefold to reach 800 µg/ml in the recombinant strain SIPI-M2093.

The Low-Alkalinity Polymyxin Derivative, AL-6, Shows High Activity Against Multidrug-Resistant Acinetobacter baumannii Clinical Isolates In Vitro and A. baumannii ATCC 19606 In Vivo: Preliminary Analysis of the Antibacterial Mechanism.

Polymyxin B and colistin (polymyxin E) are increasingly used as the last line of therapy for infections caused by multidrug-resistant (MDR) gram-negative pathogens. However, nephrotoxicity is still a limiting factor for the use of polymyxin. Therefore, better tolerated and more effective polymyxin derivatives are urgently needed. In this study, we aimed to evaluate the activity of the low-alkalinity polymyxin derivative, AL-6, against MDR Acinetobacter baumannii (Ab) clinical isolates in vitro and A. baumannii ATCC 19606 in vivo. Additionally, we performed a preliminarily study of the antibacterial mechanism. AL-6 showed much higher activity (0.125-0.25 µg/mL) against MDR A. baumannii clinical isolates than polymyxin E2 (PE2, 0.5-1 µg/mL). AL-6 also showed much higher activity (0.5-256 µg/mL) against polymyxin-resistant strains than PE2 (16-1024 µg/mL). Additionally, AL-6 showed slow resistance against A. baumannii. AL-6 also increased the survival rates of mice by 10% at 48 h compared with PE2 (5 mg/kg). AL-6 could be used at a dose of up to 10 mg/kg, increasing the survival rate to 30% at 72 h after infection. A preliminary study of the antibacterial mechanism showed that AL-6 permeabilized the outer membrane and destroyed cell membrane integrity. Moreover, there was a substantial increase in zeta potential (i.e., less negative) upon AL-6 exposure for A. baumannii. Overall, AL-6 carrying only four positive charges showed high activity against A. baumannii in vitro by disrupting cell membrane integrity. Higher doses of AL-6 could increase survival rates of mice. Thus, AL-6 may have potential applications as a bactericidal agent.

Overexpression of aveBIV leading to the improvement of 4'-epidaunorubicin production in Streptomyces coeruleorubidus strain SIPI-A0707.

The 4'-epidaunorubicin is the semisynthesis precursor of epirubicin which is a clinically useful antitumor drug thought to have slightly less cardiotoxicity than doxorubin. The 4'-epidaunorubicin was formed by overexpression of heterologous Streptomyces avermitilis aveBIV in Streptomyces coeruleorubidus SIPI-A0707 dnmV mutant blocked in the biosynthesis of daunosamine, the deoxysugar component of daunorubicin. But there was a low-yield production of 4'-epidaunorubicin. In our study, product yields were enhanced considerably by increasing aveBIV gene copy number or changing means of aveBIV integration. The 4'-epidaunorubicin titer was improved by around threefold in the recombinant strain DYG1006 with the aveBIV increased threefold copy numbers. The transcript levels of aveBIV gene meet the expectation of fermentation levels of 4'-epidaunorubicin. The method described here provides the means to produce 4'-epidaunorubicin efficiently on an industrial scale.

Molecular cloning and sequence analysis of the sisomicin biosynthetic gene cluster from Micromonospora inyoensis.

Micromonospora inyoensis produces sisomicin (Sm), an aminoglycoside antibiotic. The gene cluster of sisomicin biosynthesis spanning ca. 47 kb consists of 37 ORFs encoding various proteins for sisomicin biosynthesis, regulation, resistance and transport. The comparative genetic studies on the biosynthetic genes of sisomicin and gentamicin (Gm) reveal a similar biosynthetic route and provide a framework for the future biosynthetic studies.

A new caffeic acid tetramer from the Dracocephalum moldavica L.

A new caffeic acid tetramer compound, named (+) methyl rabdosiin (4), together with seven known caffeic acid multimers (1-3, 5-8) and one caffeic acid monomer (9), were isolated from the aerial parts of Dracocephalum moldavica L. The structures of these compounds were assigned on the basis of 1D and 2D NMR spectroscopic and mass spectrometry analyses. The protective effects of compounds 2-4 against hydrogen peroxide (H2O2)-induced apoptosis were evaluated in primary cardiomyocytes of SD neonatal rats in vitro by the MTT method. Three compounds exhibited potent protective activities at 12.5 µg/mL.

[Mechanism study on difference of biotransformation between Mycobacterium fortuitum MF2 and MF96].

Biotransformation difference between parent strain (MF2) and mutant strain (MF96) of Mycobacterium fortuitum was observed. Biotransformation with resting cells showed that the major products of biotransformation by both parent and mutant strains are delta4-androstenedione(4AD) and testosterone(TS). Experiments with cell-free extract system showed that the proportion of 4AD/TS obtained from parent and mutant strains was almost same when enough NAD+ and NADH were supplied in this system. It was suggested that the difference of the ratio of products transformed by both strains in resting cell system may result from their different ratio of NAD+/NADH. This speculation was verified to be true by determination of the amount of NAD+ and NADH presented in both strains.

[Study on cloning of sisomicin-resistant gene (sisR) from Micromonospora inyoensis].

A new sisomicin resistance gene sisR was cloned from sisomicin-producing Micromonospora inyoensis. The sisR fragment was obtained by PCR amplification. The primer pairs were designed based on grm gene sequence from gentamicin-producing Micromonospora purpurea. The template DNA was isolated from Micromonospora inyoensis. A series of different DNA fragments were amplified by PCR, which were sub-cloned to vector pUC19 for further identification. It was found that five specific transformants containing target DNA fragments could resist high concentrations of sisomicin (over 1000 microg/mL sisomicin). One of them designated as sisR, was then sequenced and the alignment among sisR and other related genes showed that sisR gene differs from any known genes. It was concluded that sisR gene is a sequence that has not been reported so far.