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) have the similar fragmentation mechanism, while Cu 2+ displayed different fragmentation mechanism due to the concurrent oxidation.

SignificanceAminoglycosides remain a vital clinical asset. Gentamicin C complex in particular is remarkably potent in treating systemic Gram-negative infections, and semisynthetic gentamicins that combat pathogen resistance or show reduced toxicity remain attractive goals. We report here the roles of clustered genes and enzymes that define a methylation network in gentamicin biosynthesis and also identify a remote gene on the chromosome encoding the essential methyltransferase GenL, which is decisive for the proportions of the five major components present in the gentamicin C complex. This is an important step toward engineered fermentation to produce single components as valuable starting materials for semisynthesis of next-generation aminoglycoside antibiotics.

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Background: The alarming spread of antimicrobial resistance requires the development of novel anti-infective drugs. Despite the recent research focus on the human microbiome and its likely value to understand and exploit inter-bacterial inhibitory phenomena as a source for antimicrobial strategies, the human microbiota has barely been investigated for the purpose of drug development. Results: We performed a large screen analyzing over 3000 human skin isolates to evaluate bacterial competition within the human skin microbiota as a basis for the development of anti-infective therapeutics. We discovered a Staphylococcus hominis strain with strong and broad activity against Gram-positive pathogens that was mediated by the bacteriocin micrococcin P1 (MP1). In "probiotic" approaches, this strain led to reduced Staphylococcus aureus infection and accelerated closure of S. aureus-infected wounds. Furthermore, we used a nanoparticle strategy to overcome the physico-chemical limitations often encountered with natural substances such as MP1 and demonstrate a significant reduction of S. aureus infection by MP1-loaded nanoparticles. Conclusions: Our study gives examples of how analysis of bacterial interactions in the human microbiota can be explored for the development of novel, effective anti-infective strategies.

Detailed analysis of the modular Type I polyketide synthase (PKS) involved in the biosynthesis of the marginolactone azalomycin F in mangrove Streptomyces sp. 211726 has shown that only nineteen extension modules are required to accomplish twenty cycles of polyketide chain elongation. Analysis of the products of a PKS mutant specifically inactivated in the dehydratase domain of extension‐module 1 showed that this module catalyzes two successive elongations with different outcomes. Strikingly, the enoylreductase domain of this module can apparently be “toggled” off and on : it functions in only the second of these two cycles. This novel mechanism expands our understanding of PKS assembly‐line catalysis and may explain examples of apparent non‐colinearity in other modular PKS systems.

Polyoxin, produced by Streptomcyes cacaoi var. asoensis and Streptomyces aureochromogenes, contains two non-proteinogenic amino acids, carbamoylpolyoxamic acid (CPOAA) and polyoximic acid. Although the CPOAA moiety is highly unusual, its biosynthetic logic has remained enigmatic for decades. Here, we address CPOAA biosynthesis by reconstitution of its pathway. We demonstrated that its biosynthesis is initiated by a versatile N-acetyltransferase, PolN, catalyzing L-glutamate (1) to N-acetyl glutamate (2). Remarkably, we verified that PolM, a previously annotated dehydrogenase, catalyzes an unprecedented tandem reduction of acyl-phosphate to aldehyde, and subsequently to alcohol. We also unveiled a distinctive acetylation cycle catalyzed by PolN to synthesize α-amino-δ-hydroxyvaleric acid (6). Finally, we report that PolL is capable of converting a rare sequential hydroxylation of α-amino-δ-carbamoylhydroxyvaleric acid (7) to CPOAA. PolL represents an intriguing family of Fe(II)-dependent α-ketoglutarate dioxygenase with a cupin fold. These data illustrate several novel enzymatic reactions, and also set a foundation for rational pathway engineering for polyoxin production.

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