ssgA Is Essential for Sporulation of Streptomyces coelicolor A3(2) and Affects Hyphal Development by Stimulating Septum Formation

The role of ssgA in cell division and development of streptomycetes was analyzed. An ssgA null mutant of Streptomyces coelicolor produced aerial hyphae but failed to sporulate, and ssgA can therefore be regarded as a novel whi gene. In addition to the morphological changes, antibiotic production was also disturbed, with strongly reduced actinorhodin production. These defects could be complemented by plasmid-borne ssgA. In the wild-type strain, transcription of ssgA was induced by nutritional shift-down and was shown to be linked to that of the upstream-located gene ssgR, which belongs to the family of iclR-type transcriptional regulator genes. Analysis of mycelium harvested from liquid-grown cultures by transmission electron microscopy showed that septum formation had strongly increased in ssgA-overexpressing strains in comparison to wild-type S. coelicolor and that spore-like compartments were produced at high frequency. Furthermore, the hyphae were significantly wider and contained irregular and often extremely thick septa. These data underline the important role for ssgA in Streptomyces cell division.

本研究对ssgA在链霉菌细胞分裂与发育过程中的作用进行了分析。天蓝色链霉菌（Streptomyces coelicolor）的ssgA缺失突变株可产生气生菌丝（aerial hyphae），但无法完成产孢过程，因此ssgA可被认定为一种新型的whi基因。除上述形态变化外，该菌株的抗生素合成通路亦受到干扰，其中放线菌紫红素（actinorhodin）的产量大幅下降。上述缺陷可通过携带ssgA的质粒实现互补恢复。在野生型菌株中，ssgA的转录可被营养浓度下调诱导，且该转录过程与上游定位的ssgR基因的转录相关，而ssgR属于iclR型转录调控因子基因家族。通过透射电子显微镜（transmission electron microscopy）对液体培养收获的菌丝体进行分析后发现，相较于野生型天蓝色链霉菌，ssgA过表达菌株的隔膜形成量显著提升，且高频产生孢子样区室。此外，该菌株的菌丝显著增粗，且隔膜形态不规则，常表现为异常增厚。上述数据进一步证实了ssgA在链霉菌细胞分裂过程中的关键作用。