Identification and Characterization of a New Erythromycin Biosynthetic Gene Cluster in <i>Actinopolyspora erythraea</i> YIM90600, a Novel Erythronolide-Producing Halophilic Actinomycete Isolated from Salt Field

<div><p>Erythromycins (Ers) are clinically potent macrolide antibiotics in treating pathogenic bacterial infections. Microorganisms capable of producing Ers, represented by <i>Saccharopolyspora erythraea</i>, are mainly soil-dwelling actinomycetes. So far, <i>Actinopolyspora erythraea</i> YIM90600, a halophilic actinomycete isolated from Baicheng salt field, is the only known Er-producing extremophile. In this study, we have reported the draft genome sequence of <i>Ac. erythraea</i> YIM90600, genome mining of which has revealed a new Er biosynthetic gene cluster encoding several novel Er metabolites. This Er gene cluster shares high identity and similarity with the one of <i>Sa. erythraea</i> NRRL2338, except for two absent genes, <i>eryBI</i> and <i>eryG</i>. By correlating genotype and chemotype, the biosynthetic pathways of 3′-demethyl-erythromycin C, erythronolide H (EH) and erythronolide I have been proposed. The formation of EH is supposed to be sequentially biosynthesized via C-6/C-18 epoxidation and C-14 hydroxylation from 6-deoxyerythronolide B. Although an <i>in vitro</i> enzymatic activity assay has provided limited evidence for the involvement of the cytochrome P450 oxidase EryF^Ac (derived from <i>Ac. erythraea</i> YIM90600) in the catalysis of a two-step oxidation, resulting in an epoxy moiety, the attempt to construct an EH-producing <i>Sa. erythraea</i> mutant via gene complementation was not successful. Characterization of EryK^Ac (derived from <i>Ac. erythraea</i> YIM90600) <i>in vitro</i> has confirmed its unique role as a C-12 hydroxylase, rather than a C-14 hydroxylase of the erythronolide. Genomic characterization of the halophile <i>Ac. erythraea</i> YIM90600 will assist us to explore the great potential of extremophiles, and promote the understanding of EH formation, which will shed new insights into the biosynthesis of Er metabolites.</p>