title: Regulation of the Type I-F CRISPR-Cas system by CRP-cAMP and GalM controls spacer acquisition and interference.
abstract: The CRISPR-Cas prokaryotic 'adaptive immune systems' represent a sophisticated defence strategy providing bacteria and archaea with protection from invading genetic elements, such as bacteriophages or plasmids. Despite intensive research into their mechanism and application, how CRISPR-Cas systems are regulated is less clear, and nothing is known about the regulation of Type I-F systems. We used Pectobacterium atrosepticum, a Gram-negative phytopathogen, to study CRISPR-Cas regulation, since it contains a single Type I-F system. The CRP-cAMP complex activated the cas operon, increasing the expression of the adaptation genes cas1 and cas2-3 in addition to the genes encoding the Csy surveillance complex. Mutation of crp or cyaA (encoding adenylate cyclase) resulted in reductions in both primed spacer acquisition and interference. Furthermore, we identified a galactose mutarotase, GalM, which reduced cas operon expression in a CRP- and CyaA-dependent manner. We propose that the Type I-F system senses metabolic changes, such as sugar availability, and regulates cas genes to initiate an appropriate defence response. Indeed, elevated glucose levels reduced cas expression in a CRP- and CyaA-dependent manner. Taken together, these findings highlight that a metabolite-sensing regulatory pathway controls expression of the Type I-F CRISPR-Cas system to modulate levels of adaptation and interference.
authors.affiliation: Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Patterson
authors.affiliation: Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: James T
authors.initials: JT
authors.lastname: Chang
authors.affiliation: Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
authors.forename: Corinda
authors.initials: C
authors.lastname: Taylor
authors.affiliation: Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin 9054, New Zealand peter.fineran@otago.ac.nz.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Fineran
mesh_terms: D001665:Binding Sites; D064130:CRISPR-Associated Proteins / Q000096:biosynthesis / Q000235:genetics*; D064113:CRISPR-Cas Systems; D002238:Carbohydrate Epimerases / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D009154:Mutation; D009876:Operon; D044043:Pectobacterium / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015533:Transcriptional Activation
chemical_list: D064130:CRISPR-Associated Proteins; D002373:Cyclic AMP Receptor Protein; D000242:Cyclic AMP; D002238:Carbohydrate Epimerases; C459183:galactose mutarotase; D005947:Glucose