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Abstract
The developmental life cycle of Streptomyces species includes aerial hyphae formation and spore maturation, two distinct developmental processes that are controlled, respectively, by two families of developmental regulatory genes, bld and whi. In this study, we show that the response regulator MtrA (SCO3013) is critical for normal development of aerial hyphae in S. coelicolor and related species. ΔmtrA, a deletion mutant of the response regulator gene mtrA, exhibited the bald phenotype typical of bld mutants defective in aerial mycelium formation, with formation either much delayed or absent depending on the culture medium. Transcriptional analysis indicated that MtrA activates multiple genes involved in formation of aerial mycelium, including chp, rdl, and ram genes, as well as developmental regulatory genes of the bld and whi families. However, the major regulatory gene bldD showed enhanced expression in ΔmtrA, suggesting it is repressed by MtrA. electrophoretic mobility shift assays indicated that MtrA binds upstream of several genes with altered expression in ΔmtrA, including bldD and whiI, and sequences similar to the consensus binding sequence for MtrA of another actinomycete, Mycobacterium tuberculosis, were found in the bound sites. A loosely conserved recognition sequence containing two short, direct repeats was identified for MtrA of S. coelicolor and was validated using mutational analysis. MtrA homologs are widely distributed among Streptomyces species, and as with S. coelicolor, deletion of the mtrA homologs sve_2757 from S. venezuelae and sli_3357 from S. lividans resulted in conditional bald morphology. Our study suggests a critical and conserved role for MtrA in Streptomyces development.
Highlights
Streptomycetes are multicellular, filamentous, Gram-positive bacteria that possess two extraordinary traits rarely seen in other prokaryotes
Our study showed that mutation of the response regulator gene mtrA leads to the bald phenotype characteristic of bld mutants, suggesting that MtrA is a new developmental regulator in
We further determined that MtrA controls multiple genes critical for development, most notably bldD, bldK, whiH, and whiI; bldD and whiI were characterized as MtrA targets through in vitro analysis
Summary
Streptomycetes are multicellular, filamentous, Gram-positive bacteria that possess two extraordinary traits rarely seen in other prokaryotes. MtrA Regulates Streptomyces Development exhibit a complex developmental life cycle, with the formation of substrate (vegetative) mycelium, aerial mycelium, and spores at different growth stages during development (Flardh and Buttner, 2009; Chater, 2011; McCormick and Flardh, 2011). Studies indicate that rodlins and chaplins interact to form the rodlet layer and that the rodlins weave chaplins into paired rodlets displaying a characteristic basketwork-like appearance on the surface of S. coelicolor spores (Wildermuth, 1970; Wildermuth et al, 1971; Claessen et al, 2002, 2004)
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