Bioinformatic evaluation of the secondary metabolism of antistaphylococcal environmental bacterial isolates.

The increasing occurrence of drug-resistant Staphylococcus aureus is exacerbated with a declining rate of antibiotic discovery, particularly those with new mechanisms of action. The decline in antibiotic discovery from traditional sources, such as soil actinobacteria, necessitates examination of lesser studied microbes. Here, we present a strategy to select for organisms that may have a propensity to result in new antistaphylococcal agents by using S. aureus as a bait organism, and selecting organisms that have a natural lytic activity towards it. We have isolated over 80 environmental isolates and typed these organisms using 16S rDNA sequence comparison and deployed bioinformatics to assess the secondary metabolic potential of the isolated antistaphylococcal bacteria using genomic sequences. Bioinformatic analysis highlights the enriched and unique suite of potential antibiotic polyketides and nonribosomal peptides and lantibiotic gene clusters from these organisms. Profiling organic microbial extracts further showed that many of the organisms from the 10 staphylolytic genera secrete agents with antistaphylococcal activity and may serve as new sources for future antistaphylococcal drug discovery.

Biosynthesis of ebelactone A: isotopic tracer, advanced precursor and genetic studies reveal a thioesterase-independent cyclization to give a polyketide ß-lactone.

Macrocyclization of polyketides generates arrays of molecular architectures that are directly linked to biological activities. The four-membered ring in oxetanones (ß-lactones) is found in a variety of bioactive polyketides (for example, lipstatin, hymeglusin and ebelactone), yet details of its molecular assembly have not been extensively elucidated. Using ebelactone as a model system, and its producer Streptomyces aburaviensis ATCC 31860, labeling with sodium [1-(13)C,(18)O2]propionate afforded ebelactone A that contains (18)O at all oxygen sites. The pattern of (13)C-(18)O bond retention defines the steps for ebelactone biosynthesis, and demonstrates that ß-lactone ring formation occurs by attack of a ß-hydroxy group onto the carbonyl moiety of an acyclic precursor. Reaction of ebelactone A with N-acetylcysteamine (NAC) gives the ß-hydroxyacyl thioester, which cyclizes quantitatively to give ebelactone A in aqueous ethanol. The putative gene cluster encoding the polyketide synthase (PKS) for biosynthesis of 1 was also identified; notably the ebelactone PKS lacks a terminal thioesterase (TE) domain and no stand alone TE was found. Thus the formation of ebelactone is not TE dependent, supporting the hypothesis that cyclization occurs on the PKS surface in a process that is modeled by the chemical cyclization of the NAC thioester.