Inactivation or amplification of the spa2 gene, encoding a potential stationary phase regulator, affects differentiation in Streptomyces ambofaciens

The deduced product of the spa2 gene of Streptomyces ambofaciens is a homologue of RspA, involved in stationary-phase sigma(s) factor regulation in Escherichia coli. This suggests that Spa2 could play a part in stationary-phase-associated differentiation in S. ambofaciens. The disruption of spa2 led to reductions in aerial mycelial development and associated spore pigmentation. The mutant phenotype reverted to the wild-type phenotype when the disruption construct spontaneously excised. The spa2 disruption had no detectable effect on growth rates in different media or antibiotic production and resistance. When spa2 was placed on a multicopy plasmid, a severe defect in formation and pigmentation of aerial mycelium resulted. These results strongly suggest that Spa2 is involved in a complex manner in the morphological differentiation process.