Griseoviridin (GV) is an A-type streptogramin antibiotic displaying antimicrobial activity and acting synergistically with viridogrisein (VG). Bioinformatic analyses reveal SgvP as the sole cytochrome P450 enzyme in the GV/VG gene cluster. To explore the role of SgvP in the GV/VG pathway, we inactivated the sgvP gene. The resulting ΔsgvP mutant generated two new products: GV-1 and GV-2, both lacking the CS bridge. In trans complementation of the sgvP gene into the ΔsgvP mutant strain partially restores GV production. Feeding [1-¹³C]-labeled cysteine to the wild-type strain led to enrichment of C-7 in the GV scaffold, thus verifying that the CS bond in GV is formed through direct coupling of the free SH group provided by the side chain of cysteine. The above results highlight the significance of SgvP in CS bond formation in griseoviridin biosynthesis.

Griseoviridin (GV) and viridogrisein (VG, also referred to as etamycin), produced by Streptomyces griseoviridis, are two chemically unrelated compounds belonging to the streptogramin family. Both of these natural products demonstrate broad-spectrum antibacterial activity and constitute excellent candidates for future drug development. To elucidate the biosynthetic machinery associated with production of these two unique antibiotics, the gene cluster responsible for both GV and VG production was identified within the Streptomyces griseoviridis genome and characterized, and its function in GV and VG biosynthesis was confirmed by inactivation of 30 genes and complementation experiments. This sgv gene cluster is localized to a 105 kb DNA region that consists of 36 open reading frames (ORFs), including four nonribosomal peptide synthetases (NRPSs) for VG biosynthesis and a set of hybrid polyketide synthases (PKS)-NRPSs with a discrete acyltransferase (AT), SgvQ, to assemble the GV backbone. The enzyme encoding genes for VG versus GV biosynthesis are separated into distinct “halves” of the cluster. A series of four genes: sgvA, sgvB, sgvC, and sgvK, were found downstream of the PKS-NRPS; these likely code for construction of a γ-butyrolactone (GBL)-like molecule. GBLs and the corresponding GBL receptor systems are the highest ranked regulators that are able to coordinate the two streptomyces antibiotic regulatory protein (SARP) family positive regulators SgvR2 and SgvR3; both are key biosynthetic activators. Models of GV, VG, and GBL biosynthesis were proposed by using functional gene assignments, determined on the basis of bioinformatics analysis and further supported by in vivo gene inactivation experiments. Overall, this work provides new insights into the biosyntheses of the GV and VG streptogramins that are potentially applicable to a host of combinatorial biosynthetic scenarios.

The nine-membered indolactam antibiotics belong to a small group of antibiotics showing broad biological activities. However, the in vivo genetic engineering of compounds of this type has not been performed. Here we report the identification of a single gene cluster responsible for the biosynthesis of methylpendolmycin and pendolmycin, two members of this family of antibiotics, from the deep sea bacterium Marinactinospora thermotolerans SCSIO 00652. Bioinformatics analysis and gene inactivation, coupled with metabolite characterization, reveal that MpnB, a nonribosomal peptide synthetase, MpnC, a cytochrome P450, and MpnD, a prenyltransferase, are sufficient to catalyze the biosynthesis of the two antibiotics from L-Ile (or L-Val), L-Trp, and methionine. MpnD is the first identified enzyme that transfers a C5 prenyl unit in a reverse manner to the C-7 position of a Trp-derived natural product.

Two new cytochalasins, 18-deoxycytochalasin Q (1) and 21-O-deacetylcytochalasin Q (2), together with four known analogues, cytochalasin Q (3), 19,20-epoxycytochalasin Q (4), 21-O-deacetyl-19,20-epoxycytochalasin Q (5), and cytochalasin D (6), were isolated from the fungus Xylaria sp. SCSIO156 originated from the South China Sea marine sediment. The structures of 1 and 2 were elucidated by MS and 1D- and 2D-NMR data analyses, and comparison with known compounds. The known compounds 3–6 were identified by comparison of their MS and NMR data with those reported in the literature. In the in vitro antitumor assay, compounds 2–6 showed mild cytotoxicity against three tumor cell lines (MCF-7, SF-268, and NCI-H460).