Genome-scale CRISPRi and base-editing libraries for genetic decoding and strain engineering in Shewanella

Clustered regularly interspaced short palindromic repeats (CRISPR)-based libraries with diverse gene-editing functions, such as gene knockdown and mutation, can significantly accelerate our understanding of complex metabolic networks in microorganisms, particularly for species beyond classical model organisms. Here, three distinct CRISPR-based libraries were designed in the electroactive microorganism Shewanella oneidensis MR-1: a CRISPR interference (CRISPRi) library covering 99.6% of genes in the genome, a protein mutation library focused on genes involved in carbon metabolism, and an inactivation library, with sizes of 30 804, 5963, and 4072 single guide (sg)RNAs, respectively. The principles for the design and construction of libraries were validated, and a conjugation-based library transformation method with high coverage and uniformity was developed. For the first time, we explored the potential essential genes of S. oneidensis MR-1, and expanded the substrate spectrum available for electricity generation, including glucose and chitin. These efforts enable deeper genomic interrogation of Shewanella, and provide a framework for applying genome-scale CRISPR-based tools to other undercharacterized microbial species.