The Product of a Developmental Gene, crgA , That Coordinates Reproductive Growth in Streptomyces Belongs to a Novel Family of Small Actinomycete-Specific Proteins

Abstract

On solid media, the reproductive growth of Streptomyces involves antibiotic biosynthesis coincident with the erection of filamentous aerial hyphae. Following cessation of growth of an aerial hypha, multiple septation occurs at the tip to form a chain of unigenomic spores. A gene, crgA, that coordinates several aspects of this reproductive growth is described. The gene product is representative of a well-conserved family of small actinomycete proteins with two C-terminal hydrophobic-potential membrane-spanning segments. In Streptomyces avermitilis, crgA is required for sporulation, and inactivation of the gene abolished most sporulation septation in aerial hyphae. Disruption of the orthologous gene in Streptomyces coelicolor indicates that whereas CrgA is not essential for sporulation in this species, during growth on glucose-containing media, it influences the timing of the onset of reproductive growth, with precocious erection of aerial hyphae and antibiotic production by the mutant. Moreover, CrgA subsequently acts to inhibit sporulation septation prior to growth arrest of aerial hyphae. Overexpression of CrgA in S. coelicolor, uncoupling any nutritional and growth phase-dependent regulation, results in growth of nonseptated aerial hyphae on all media tested, consistent with a role for the protein in inhibiting sporulation septation.Reproductive growth of gram-positive Streptomyces involves the formation of filamentous aerial hyphae that metamorphose into chains of unigenomic spores, as exemplified by the model species, Streptomyces coelicolor (5, 6). The growth of aerial hyphae is away from the nutrient source, fueled partly by cannibalization of lysing substrate mycelia. In plate-grown cultures, antibiotic production (physiological differentiation) is generally coincident with morphological differentiation, and released antibiotics may serve to protect a differentiating colony from predation in a natural soil habitat. Mutants affected in early reproductive growth fail to erect aerial hyphae, and the corresponding bld genes often pleiotropically influence antibiotic production. Genes involved in later stages of spore formation include the whi genes, so named because mutations in these genes prevent either formation of spore compartments (early whi genes) or subsequent spore maturation events (late whi genes), which include production of a grey-brown sporeassociated pigment (reviewed in reference 6). Most of these whi genes appear to encode regulatory functions. Among the early whi genes, whiG encodes an alternative sigma factor (29); whiA encodes a protein of unknown function (2); whiB encodes a small, highly charged, and cysteine-rich protein of unknown function (20); whiH encodes a member of the GntR family of transcription factors (24); and whiI encodes a protein resembling the response regulator of a two-component sensor-regulator system, although there is no adjacent recognizable kinase gene and WhiI itself lacks important amino acid residues normally needed for phosphorylation to take place (1). On the ...

Signals and regulators that governStreptomycesdevelopment

“…It has been unclear how this developmental control of Z ring assembly is brought about as streptomycetes and other Actinobacteria lack clear homologs of most of the proteins that in other bacteria are involved in the control of FtsZ assembly, stabilization of the Z ring, and anchoring of the ring to the cytoplasmic membrane (see discussions in Flärdh & Buttner, ; McCormick, ). The small transmembrane protein CrgA was implicated in the control of cell division for S. coelicolor (Del Sol et al ., , ), and this is supported by a report showing septal targeting and interaction of CrgA with FtsZ and other division proteins in M. tuberculosis (Plocinski et al ., ).…”

Alignment of multiple chromosomes along helical ParA scaffolding in sporulating Streptomyces hyphae

“…Possibly, Streptomyces ParA also plays a role in co‐ordinating chromosome segregation with cell division. Apart from ParA, additional proteins (Ssg family, CrgA) have been described that have effects on sporulation septation, but their modes of action and whether they affect the cell division machinery directly or indirectly are not clear (van Wezel et al ., 2000; Del Sol et al ., 2003; Keijser et al ., 2003). Currently, we are screening for ParA interaction with the other proteins engaged in development of aerial hyphae.…”

Developmental biology ofStreptomycesfrom the perspective of 100 actinobacterial genome sequences

“…The near-universal actinobacterial protein CrgA (Table 1 , Fig. 9 ) has been studied in two streptomycetes (Del Sol et al ., 2003 , 2006 ) and in M. tuberculosis and M. smegmatis (Plocinski et al ., 2011 , 2012 ). It is a small protein with a C-terminal transmembrane domain.…”

“…The overexpression of CrgA inhibits septation (Del Sol et al ., 2006 ), an effect that could be a secondary consequence of the over-occupation by CrgA of its various interaction partners. Interestingly, crgA mutants of streptomycetes do not always have the same phenotype: an S. coelicolor mutant shows premature production of spores that are slightly aberrant, but in the S. avermitilis mutant, sporulation septation does not take place (Del Sol et al ., 2003 ).…”