Table1.XLSX

Extracytoplasmic function (ECF) sigma factors are a major type of bacterial signal-transducers whose biological functions remain poorly characterized in streptomycetes. In this work we studied SCO4117, a conserved ECF sigma factor from the ECF52 family overexpressed during substrate and aerial mycelium stages. The ECF52 sigma factors harbor, in addition to the ECF sigma factor domain, a zinc finger domain, a transmembrane region, a proline-rich C-terminal extension, and a carbohydrate-binding domain. This class of ECF sigma factors is exclusive to Actinobacteria. We demonstrate that SCO4117 is an activator of secondary metabolism, aerial mycelium differentiation, and sporulation, in all the culture media (sucrose-free R5A, GYM, MM, and SFM) analyzed. Aerial mycelium formation and sporulation are delayed in a SCO4117 knockout strain. Actinorhodin production is delayed and calcium-dependent antibiotic production is diminished, in the ΔSCO4117 mutant. By contast, undecylprodigiosin production do not show significant variations. The expression of genes encoding secondary metabolism pathways (deoxysugar synthases, actinorhodin biosynthetic genes) and genes involved in differentiation (rdl, chp, nepA, ssgB) was dramatically reduced (up to 300-fold) in the SCO4117 knockout. A putative motif bound, with the consensus “CSGYN-17bps-SRHA” sequence, was identified in the promoter region of 29 genes showing affected transcription in the SCO4117 mutant, including one of the SCO4117 promoters. SCO4117 is a conserved gene with complex regulation at the transcriptional and post-translational levels and the first member of the ECF52 family characterized.

胞质外功能σ因子（Extracytoplasmic function, ECF）是一类主要的细菌信号转导蛋白，但其在链霉菌中的生物学功能仍未得到充分解析。本研究针对SCO4117展开了探究：该蛋白是隶属于ECF52家族的保守ECF σ因子，在基内菌丝与气生菌丝阶段均会出现过表达。ECF52家族σ因子除携带ECF σ因子结构域外，还包含锌指结构域、跨膜区域、富含脯氨酸的C端延伸区以及碳水化合物结合结构域。该类ECF σ因子仅存在于放线菌门（Actinobacteria）中。本研究证实，在所分析的所有培养基（不含蔗糖的R5A、GYM、MM及SFM培养基）中，SCO4117均可作为次级代谢、气生菌丝分化以及孢子形成的激活因子。SCO4117敲除菌株的气生菌丝形成与孢子形成过程均出现延迟；ΔSCO4117突变株中，放线菌素的合成出现延迟，钙依赖性抗生素的产量也有所降低，而十一烷基灵菌红素的产量则未出现显著变化。在SCO4117敲除菌株中，编码次级代谢通路的基因（如脱氧糖合酶、放线菌素生物合成基因）以及参与分化过程的基因（rdl、chp、nepA、ssgB）的表达量均显著下调，最高下调幅度可达300倍。研究人员在SCO4117突变株中转录水平受影响的29个基因的启动子区域中，鉴定出了一个共有序列为"CSGYN-17bps-SRHA"的潜在结合基序，其中包含一个SCO4117的启动子。SCO4117是一类保守基因，其转录与翻译后水平的调控机制较为复杂，同时也是ECF52家族中首个得到功能鉴定的成员。