Identification and utilization of two important transporters: SgvT1 and SgvT2, for griseoviridin and viridogrisein biosynthesis in Streptomyces griseoviridis

Yunchang Xie,Qinglian Li,Junying Ma,Jianhua Ju,Xiangjing Qin

doi:10.1186/s12934-017-0792-8

Abstract

BackgroundGriseoviridin (GV) and viridogrisein (VG, also referred as etamycin), both biosynthesized by a distinct 105 kb biosynthetic gene cluster (BGC) in Streptomyces griseoviridis NRRL 2427, are a pair of synergistic streptogramin antibiotics and very important in treating infections of many multi-drug resistant microorganisms. Three transporter genes, sgvT1–T3 have been discovered within the 105 kb GV/VG BGC, but the function of these efflux transporters have not been identified.ResultsIn the present study, we have identified the different roles of these three transporters, SgvT1, SgvT2 and SgvT3. SgvT1 is a major facilitator superfamily (MFS) transporter whereas SgvT2 appears to serve as the sole ATP-binding cassette (ABC) transporter within the GV/VG BGC. Both proteins are necessary for efficient GV/VG biosynthesis although SgvT1 plays an especially critical role by averting undesired intracellular GV/VG accumulation during biosynthesis. SgvT3 is an alternative MFS-based transporter that appears to serve as a compensatory transporter in GV/VG biosynthesis. We also have identified the γ-butyrolactone (GBL) signaling pathway as a central regulator of sgvT1–T3 expression. Above all, overexpression of sgvT1 and sgvT2 enhances transmembrane transport leading to steady production of GV/VG in titers ≈ 3-fold greater than seen for the wild-type producer and without any notable disturbances to GV/VG biosynthetic gene expression or antibiotic control.ConclusionsOur results shows that SgvT1–T2 are essential and useful in GV/VG biosynthesis and our effort highlight a new and effective strategy by which to better exploit streptogramin-based natural products of which GV and VG are prime examples with clinical potential.

Highlights

Griseoviridin (GV) and viridogrisein (VG, referred as etamycin), both biosynthesized by a distinct 105 kb biosynthetic gene cluster (BGC) in Streptomyces griseoviridis NRRL 2427, are a pair of synergistic streptogramin antibiotics and very important in treating infections of many multi-drug resistant microorganisms
Enabled by the recently identified 105-kb GV/VG biosynthetic gene cluster (Fig. 2) [1, 2], we report : (i) the identification of three transporter encoding genes housed within the GV/VG biosynthetic gene cluster: sgvT1–T3 (SgvT1 and SgvT3 are major facilitator superfamily (MFS) transporters and SgvT2 is an ATP-binding cassette (ABC) transporter) that are regulated by γ-butyrolactone (GBL)-type signaling, (ii) SgvT1 and SgvT2 are both necessary for efficient GV/ VG biosynthesis with SgvT1 playing an indispensable role in maintaining stable expression throughout sustainable GV/VG biosynthesis, and (iii) a roughly threefold increase in GV/VG titers resulting from sgvT1–T2 overexpression
Discovery of SgvT1–T3 as a two class‐based transporter system Streptomyces griseoviridis NRRL 2427 is a well-known producer of GV and VG; the highest yield of GV is 33.04 ± 0.70 μg/mL and that of VG is 31.56 ± 0.51 μg/mL both over the course of 108 h fermentation

Summary

Introduction

Griseoviridin (GV) and viridogrisein (VG, referred as etamycin), both biosynthesized by a distinct 105 kb biosynthetic gene cluster (BGC) in Streptomyces griseoviridis NRRL 2427, are a pair of synergistic streptogramin antibiotics and very important in treating infections of many multi-drug resistant microorganisms. Stemming from the diversity of structures and bioactivities of their secondary metabolites, the streptograminproducing actinomycetes commonly employ several transmembrane transporters as drug efflux pumps to avoid intracellular metabolite accumulation These transporters typically belong to major facilitator superfamily (MFS) and ATP-binding cassette (ABC) families and constitute an essential self-resistance mechanism to efficiently secrete antibiotics as they are constructed thereby protecting the producing microbe from the effects of its own secondary metabolism [5,6,7,8,9,10]. This is a central idea in microbial homeostasis [11,12,13,14]. The majority of prokaryotic ABC transporters consist of stand-alone TMD or NBD polypeptides which must dimerize in some fashion to generate fully functional proteins [12, 17]

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