The regulatory role of MtrA and NsrR in streptomyces coelicolor
Streptomyces coelicolor inhabits a harsh soil environment, which it must adapt and respond to; therefore how S. coelicolor senses and responds to its environment is of the utmost importance. This project addresses two types of regulation system: the three-component system MtrAB-LpqB and the nitrite-sensitive repressor NsrR. Previous work involving the response regulator MtrA has resulted in the hypothesis that MtrA regulates cell division within actinomycetes. However the role of MtrAB-LpqB within S. coelicolor has not been investigated. Therefore it is important to establish whether cell division is disrupted within mutants of the sco3014-lpqB operon. Removing components of the MtrAB-LpqB system resulted in actinorhodin production and spore formation being altered. The irregular spore structure seen by scanning electron microscopy (SEM) may be due to the difference in ftsZ expression, which could account for the irregularly placed septum and spore size observed. Therefore this work confirms that MtrAB-LpqB is important for cell division within S. coelicolor. Work was also carried out on the repressor NsrR to establish its role within S. coelicolor as previous findings had primarily focused on the type of Fe-S cluster contained within NsrR. The phenotype of an nsrR mutant exhibited a low level of spore production, similar to the distinctive, development whi phenotype. Some Whi proteins function via an [4Fe-4S] cluster, which is also central to NsrR regulation meaning NsrR could be linked to the Whi proteins within S. coelicolor. To understand NsrR function further, ChIP-seq was undertaken to identify direct targets; revealing, contrary to prediction studies, NsrR represses only three targets: hmpA1, hmpA2 and nsrR. These targets were confirmed by in vitro binding studies with purified S. coelicolor NsrR. Therefore this work reveals that NsrR undergoes auto-regulation and its sole role is to regulate nitric oxide (NO) stress response via detoxification within S. coelicolor.
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