Mixing and Matching Genes of Marine and Terrestrial Origin in the Biosynthesis of the Mupirocin Antibiotics

With growing understanding of the underlying pathways of polyketide biosynthesis, along with the continual expansion of the synthetic biology toolkit, it is becoming possible to rationally engineer and fine-tune the polyketide biosynthetic machinery for production of new compounds with improved properties such as stability and/or bioactivity. However, engineering the pathway to the thiomarinol antibiotics has proved challenging. Here we report that genes from a marine Pseudoalternomonas sp. producing thiomarinol can be expressed in functional form in the biosynthesis of the clinically important antibiotic mupirocin from the soil bacterium Pseudomonas fluorescens. It is revealed that both pathways employ the same unusual mechanism of tetrahydropyran (THP) ring formation and the enzymes are cross compatible. Furthermore, the efficiency of downstream processing of 10,11-epoxy versus 10,11-alkenic metabolites are comparable. Optimisation of the fermentation conditions in an engineered strain in which production of pseudomonic acid A (with the 10,11-epoxide) is replaced by substantial titres of the more stable pseudomonic acid C (with a 10,11-alkene) pave the way for its development as a more stable antibiotic with wider applications than mupirocin

A Natural Plasmid Uniquely Encodes Two Biosynthetic Pathways Creating a Potent Anti-MRSA Antibiotic

Background Understanding how complex antibiotics are synthesised by their producer bacteria is essential for creation of new families of bioactive compounds. Thiomarinols, produced by marine bacteria belonging to the genus Pseudoalteromonas, are hybrids of two independently active species: the pseudomonic acid mixture, mupirocin, which is used clinically against MRSA, and the pyrrothine core of holomycin. Methodology/Principal Findings High throughput DNA sequencing of the complete genome of the producer bacterium revealed a novel 97 kb plasmid, pTML1, consisting almost entirely of two distinct gene clusters. Targeted gene knockouts confirmed the role of these clusters in biosynthesis of the two separate components, pseudomonic acid and the pyrrothine, and identified a putative amide synthetase that joins them together. Feeding mupirocin to a mutant unable to make the endogenous pseudomonic acid created a novel hybrid with the pyrrothine via “mutasynthesis” that allows inhibition of mupirocin-resistant isoleucyl-tRNA synthetase, the mupirocin target. A mutant defective in pyrrothine biosynthesis was also able to incorporate alternative amine substrates. Conclusions/Significance Plasmid pTML1 provides a paradigm for combining independent antibiotic biosynthetic pathways or using mutasynthesis to develop a new family of hybrid derivatives that may extend the effective use of mupirocin against MRSA

Cladobotric acids: Metabolites from cultures of Cladobotryum sp., semi-synthetic analogues and antibacterial activity

[Image: see text] Three new polyketide-derived natural products, cladobotric acids G–I (1–3), and six known metabolites (4, 5, 8–11) were isolated from fermentation of the fungus Cladobotryum sp. grown on rice. Their structures were elucidated by extensive spectroscopic methods. Two metabolites, cladobotric acid A (4) and pyrenulic acid A (10), were converted to a series of new products (12–20) by semisynthesis. The antibacterial activities of all these compounds were investigated against the Gram-positive pathogen Staphylococcus aureus including methicillin-susceptible (MSSA), methicillin-resistant and vancomycin-intermediate (MRSA/VISA), and heterogeneous vancomycin-intermediate (hVISA) strains. Results of these antibacterial assays revealed structural features of the unsaturated decalins important for biological activity

Heterologous expression of the avirulence gene ACE1 from the fungal rice pathogen Magnaporthe oryzae

The ACE1 and RAP1 genes from the avirulence signalling gene cluster of the rice blast fungus Magnaporthe oryzae were expressed in Aspergillus oryzae and M. oryzae itself. Expression of ACE1 alone produced a polyenyl pyrone (magnaporthepyrone), which is regioselectively epoxidised and hydrolysed to give different diols, 6 and 7, in the two host organisms. Analysis of the three introns present in ACE1 determined that A. oryzae does not process intron 2 correctly, while M. oryzae processes all introns correctly in both appressoria and mycelia. Co-expression of ACE1 and RAP1 in A. oryzae produced an amide 8 which is similar to the PKS-NRPS derived backbone of the cytochalasans. Biological testing on rice leaves showed that neither the diols 6 and 7, nor amide 8 was responsible for the observed ACE1 mediated avirulence, however, gene cluster analysis suggests that the true avirulence signalling compound may be a tyrosine-derived cytochalasan compound.Government of Egypt ScholarshipThe School of Chemistry at the University of Bristol and the Mark Evans ScholarshipKano State Government NigeriaMacArthur FoundationBayero UniversityNigerian Petroleum Technology FundMalaysian Govenment ScholarshipEP/F066104/

Uncovering Biosynthetic Relationships Between Antifungal Nonadrides and Octadrides

Maleidrides are a class of bioactive secondary metabolites unique to filamentous fungi, which contain one or more maleic anhydrides fused to a 7-, 8- or 9- membered carbocycle (named heptadrides, octadrides and nonadrides respectively). Herein structural and biosynthetic studies on the antifungal octadride, zopfiellin, and nonadrides scytalidin, deoxyscytalidin and castaneiolide are described. A combination of genome sequencing, bioinformatic analyses, gene disruptions, biotransformations, isotopic feeding studies, NMR and X-ray crystallography revealed that they share a common biosynthetic pathway, diverging only after the nonadride deoxyscytalidin. 5-Hydroxylation of deoxyscytalidin occurs prior to ring contraction in the zopfiellin pathway of Diffractella curvata. In Scytalidium album, 6-hydroxylation-confirmed as being catalysed by the α-ketoglutarate dependent oxidoreductase ScyL2-converts deoxyscytalidin to scytalidin, in the final step in the scytalidin pathway. Feeding scytalidin to a zopfiellin PKS knockout strain led to the production of the nonadride castaneiolide and two novel ring-open maleidrides. © The Royal Society of Chemistry

Characterisation of the biosynthetic pathway to agnestins A and B reveals the reductive route to chrysophanol in fungi

Two new dihydroxy-xanthone metabolites, agnestins A and B, were isolated from Paecilomyces variotii along with a number of related benzophenones and xanthones including monodictyphenone. The structures were elucidated by NMR analyses and X-ray crystallography. The agnestin (agn) biosynthetic gene cluster was identified and targeted gene disruptions of the PKS, Baeyer-Villiger monooxygenase, and other oxido-reductase genes revealed new details of fungal xanthone biosynthesis. In particular, identification of a reductase responsible for in vivo anthraquinone to anthrol conversion confirms a previously postulated essential step in aromatic deoxygenation of anthraquinones, e.g. emodin to chrysophanol

Elucidation of the relative and absolute stereochemistry of the kalimantacin/batumin antibiotics

A multidisciplinary approach combining natural product degradation, fragment synthesis, bioinformatics and NMR spectroscopy was used.</p