Matilla Miguel A, Leeper Finian J, Salmond George P C
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK.
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Environ Microbiol. 2015 Aug;17(8):2993-3008. doi: 10.1111/1462-2920.12839. Epub 2015 Apr 8.
Polyketides represent an important class of bioactive natural products with a broad range of biological activities. We identified recently a large trans-acyltransferase (AT) polyketide synthase gene cluster responsible for the biosynthesis of the antifungal, anti-oomycete and antitumor haterumalide, oocydin A (ooc). Using genome sequencing and comparative genomics, we show that the ooc gene cluster is widespread within biocontrol and phytopathogenic strains of the enterobacteria, Serratia and Dickeya. The analysis of in frame deletion mutants confirmed the role of a hydroxymethylglutaryl-coenzyme A synthase cassette, three flavin-dependent tailoring enzymes, a free-standing acyl carrier protein and two hypothetical proteins in oocydin A biosynthesis. The requirement of the three trans-acting AT domains for the biosynthesis of the macrolide was also demonstrated. Expression of the ooc gene cluster was shown to be positively regulated by an N-acyl-L-homoserine lactone-based quorum sensing system, but operating in a strain-dependent manner. At a post-transcriptional level, the RNA chaperone, Hfq, plays a key role in oocydin A biosynthesis. The Hfq-dependent regulation is partially mediated by the stationary phase sigma factor, RpoS, which was also shown to positively regulate the synthesis of the macrolide. Our results reveal differential regulation of the divergently transcribed ooc transcriptional units, highlighting the complexity of oocydin A production.
聚酮化合物是一类重要的具有广泛生物活性的生物活性天然产物。我们最近鉴定出一个大型反式酰基转移酶（AT）聚酮合酶基因簇，该基因簇负责抗真菌、抗卵菌和抗肿瘤的哈特勒马利德、卵霉素A（ooc）的生物合成。通过基因组测序和比较基因组学，我们发现ooc基因簇在肠杆菌科的生防菌株和植物致病菌株、沙雷氏菌属和迪基氏菌属中广泛存在。对框内缺失突变体的分析证实了羟甲基戊二酰辅酶A合酶盒、三种黄素依赖性修饰酶、一个独立的酰基载体蛋白和两个假定蛋白在卵霉素A生物合成中的作用。还证明了三个反式作用AT结构域对大环内酯生物合成的必要性。结果表明，ooc基因簇的表达受基于N-酰基-L-高丝氨酸内酯的群体感应系统正调控，但调控方式因菌株而异。在转录后水平，RNA伴侣Hfq在卵霉素A生物合成中起关键作用。Hfq依赖性调控部分由稳定期σ因子RpoS介导，RpoS也被证明对大环内酯的合成起正调控作用。我们的结果揭示了不同转录的ooc转录单元的差异调控，突出了卵霉素A产生的复杂性。
