title: ThedevOperon Regulates the Timing of Sporulation during Myxococcus xanthus Development.
abstract: Myxococcus xanthusundergoes multicellular development when starved. Thousands of rod-shaped cells coordinate their movements and aggregate into mounds in which cells differentiate into spores. Mutations in thedevoperon impair development. Thedevoperon encompasses a clustered regularly interspaced short palindromic repeat-associated (CRISPR-Cas) system. Null mutations indevI, a small gene at the beginning of thedevoperon, suppress the developmental defects caused by null mutations in the downstreamdevRanddevSgenes but failed to suppress defects caused by a small in-frame deletion indevTWe provide evidence that the original mutant has a second-site mutation. We show thatdevTnull mutants exhibit developmental defects indistinguishable fromdevRanddevSnull mutants, and a null mutation indevIsuppresses the defects of adevTnull mutation. The similarity of DevTRS proteins to components of the CRISPR-associated complex for antiviral defense (Cascade), together with our molecular characterization ofdevmutants, support a model in which DevTRS form a Cascade-like subcomplex that negatively autoregulatesdevtranscript accumulation and prevents DevI overproduction that would strongly inhibit sporulation. Our results also suggest that DevI transiently inhibits sporulation when regulated normally. The mechanism of transient inhibition may involve MrpC, a key transcription factor, whose translation appears to be weakly inhibited by DevI. Finally, our characterization of adevI devSmutant indicates that very littleexotranscript is required for sporulation, which is surprising since Exo proteins help form the polysaccharide spore coat.IMPORTANCECRISPR-Cas systems typically function as adaptive immune systems in bacteria. ThedevCRISPR-Cas system ofM. xanthushas been proposed to prevent bacteriophage infection during development, but howdevcontrols sporulation has been elusive. Recent evidence supported a model in which DevR and DevS prevent overproduction of DevI, a predicted 40-residue inhibitor of sporulation. We provide genetic evidence that DevT functions together with DevR and DevS to prevent DevI overproduction. We also show that spores form about 6 h earlier in mutants lackingdevIthan in the wild type. Only a minority of natural isolates appear to have a functionaldevpromoter anddevI, suggesting that a functionaldevCRISPR-Cas system evolved recently in niches where delayed sporulation and/or protection from bacteriophage infection proved advantageous.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA.
authors.forename: Ramya
authors.initials: R
authors.lastname: Rajagopalan
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA kroos@msu.edu.
authors.forename: Lee
authors.initials: L
authors.lastname: Kroos
mesh_terms: D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D055786:Gene Knockout Techniques; D009154:Mutation; D016941:Myxococcus xanthus / Q000235:genetics* / Q000254:growth & development*; D009876:Operon; D013171:Spores, Bacterial / Q000235:genetics* / Q000254:growth & development*; D013995:Time
keywords: CRISPR-Cas; Myxococcus xanthus; bacterial development; dev operon; gene regulation; signaling; sporulation