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

Abstract

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.

Taxonomy, Physiology, and Natural Products of Actinobacteria

“…SsgA activates sporulation-specific cell division (312,313), and both ssgA and ssgB are required for sporulation (275,314,315). The symmetrical spacing of the many Z-rings is achieved by SsgB, which directly recruits FtsZ and also stimulates its polymerization (316).…”

Positive control of cell division: FtsZ is recruited by SsgB during sporulation ofStreptomyces

“…We demonstrated previously that SsgA marks the sites where the cell wall needs to be remodeled; namely, during apical growth, branching, germination, and cell division (Noens et al 2007). High-level overexpression of SsgA induces submerged sporulation in vegetative hyphae of S. coelicolor (which normally forms only dense mycelial clumps) (van Wezel et al 2000a) and affects hypergermination, with up to eight germ tubes protruding from a single spore (Noens et al 2007). It is rather unlikely that SsgA acts in all of these cases via interaction with (and localization of) SsgB.…”

“…S. coelicolor M145 was obtained from the John Innes Centre strain collection, and the S. coelicolor ftsZ mutant HU133 (McCormick et al 1994) was kindly provided by Joe McCormick; the ssgA and ssgB mutants of S. coelicolor were published previously (van Wezel et al 2000a;Keijser et al 2003). FM145 is a spontaneous low-autofluorescent derivative of M145 (Willemse and van Wezel 2009).…”

“…SsgA is a member of the family of SsgA-like proteins (SALPs), with seven orthologs in S. coelicolor (Noens et al 2005;Traag and van Wezel 2008). Null mutants of ssgA and ssgB are blocked at a stage preceding the onset of sporulationspecific cell division, suggesting they may play a role in the control of this process (van Wezel et al 2000a;Keijser et al 2003). Interestingly, while SsgA has a major impact on morphogenesis, its expression is independent of the early whi genes, which regulate the different stages of aerial development and sporulation (Chater 2001;Traag et al 2004).…”

The autoregulator receptor homologue AvaR3 plays a regulatory role in antibiotic production, mycelial aggregation and colony development of Streptomyces avermitilis

“…Recently, two factors have been reported to be involved in the process of mycelial aggregation: SsgA, which is an activator of sporulation-specific cell division (Traag & van Wezel, 2008), and CslA, which is involved in polysaccharide synthesis at the outer surface of hyphae (de Jong et al, 2009). The enhanced expression of ssgA leads to mycelial fragmentation in S. coelicolor A3(2) and S. griseus (Kawamoto et al, 1997;van Wezel et al, 2000), whereas the cslA mutation reduces the degree of mycelial aggregation in S. coelicolor A3(2) (Xu et al, 2008). We have demonstrated in this study that the avaR3 mutation results in fragmented growth in liquid culture.…”