{"title":"Type I CRISPR-Cas immunity primes type III spacer acquisition.","authors":"Leah M Smith, Peter C Fineran","doi":"10.1016/j.chom.2025.07.021","DOIUrl":null,"url":null,"abstract":"<p><p>CRISPR-Cas systems are diverse, with microbes harboring multiple classes and subtypes. Type I DNA-targeting and type III RNA-targeting systems often co-occur, but their interactions remain unclear. Prodigiosinella has three CRISPR-Cas systems (I-E, I-F, and III-A) with independent adaptation machinery. Type III systems can trigger cell death, yet it is unknown how functional spacers are acquired. We found that type I interference generates substrates acquired by the type III adaptation machinery. Despite reducing type I interference efficiency, type III contributed to plasmid loss and provided an advantage when DNA-targeting systems failed. Type I priming influenced type III spacer length and source, with more spacers acquired near the type I target site. Invader DNA clearance by type I interference enabled retention of cytotoxic type III spacers that would otherwise be lost. This study reveals how RNA-targeting CRISPR-Cas systems function as a backup in multi-system hosts, bolstering population-level protection.</p>","PeriodicalId":93926,"journal":{"name":"Cell host & microbe","volume":" ","pages":"1561-1576.e6"},"PeriodicalIF":18.7000,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Cell host & microbe","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1016/j.chom.2025.07.021","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"2025/8/18 0:00:00","PubModel":"Epub","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
CRISPR-Cas systems are diverse, with microbes harboring multiple classes and subtypes. Type I DNA-targeting and type III RNA-targeting systems often co-occur, but their interactions remain unclear. Prodigiosinella has three CRISPR-Cas systems (I-E, I-F, and III-A) with independent adaptation machinery. Type III systems can trigger cell death, yet it is unknown how functional spacers are acquired. We found that type I interference generates substrates acquired by the type III adaptation machinery. Despite reducing type I interference efficiency, type III contributed to plasmid loss and provided an advantage when DNA-targeting systems failed. Type I priming influenced type III spacer length and source, with more spacers acquired near the type I target site. Invader DNA clearance by type I interference enabled retention of cytotoxic type III spacers that would otherwise be lost. This study reveals how RNA-targeting CRISPR-Cas systems function as a backup in multi-system hosts, bolstering population-level protection.