The role of two major nucleoid associated proteins in Streptomyces, HupA and HupS, in stress survival and gene expression regulation
Streptomyces are sporulating soil bacteria with enormous potential for secondary metabolites biosynthesis. Regulatory networks governing Streptomyces coelicolor differentiation and secondary metabolites production are complex and composed of numerous regulatory proteins ranging from specific transcriptional regulators to sigma factors. Nucleoid associated proteins (NAPs) are also believed to contribute to regulation of gene expression. Upon DNA binding these proteins impact DNA accessibility. Among NAPs HU proteins are the most widespread and abundant. Unlike other bacteria, the Streptomyces genome encodes two HU homologs: HupA and HupS, differing in structure and expression profile. In this study, we explore whether HupA and HupS affect S. coelicolor growth under optimal and stressful conditions and how they control global gene expression. By testing both single and double mutants we address the question of both HU homologs complementarity. The lack of both hup genes led to growth and sporulation inhibition, as well as increased spore fragility. Our data indicate a synergy between the functions of HupA and HupS during S. coelicolor growth. We also demonstrate, that both HU homologs can be considered global transcription regulators influencing expression of numerous genes encoding proteins linked to chromosome topology, secondary metabolites production and transcription. We identify the independent HupA and HupS regulons as well as genes under the control of both HupA and HupS proteins. Our data indicate some extent of redundancy as well as independent function of both homologs. ImportanceStreptomyces belong to the bacterial family widely used in the production of antibiotics as well as research for new bioactive substances with antimicrobial properties. Gene expression in Streptomyces, and consequently the production of secondary metabolites, is controlled by a vast and complex network of transcriptional regulators. Our data indicate that two proteins, HupA and HupS, involved in the maintenance of chromosome structure, also participate in this regulatory network. Their presence appears to important for S. coelicolors adaptation for survival in unfavorable conditions such as high temperature. The lack of one or both HU proteins affects the expression of many genes, indicating that they act as global transcriptional regulators.