Genome-wide CRISPRi screen identifies enhanced autolithotrophic phenotypes in acetogenic bacterium Eubacterium limosum

Acetogenic bacteria are a unique biocatalyst that highly promises to develop the sustain-able bioconversion of carbon oxides (e.g., CO and CO2) into multicarbon biochemicals. Genotype-phenotype relationships are important for engineering their metabolic capa-bility to enhance their biocatalytic performance; however, systemic investigation on the fitness contribution of individual gene has been limited. Here, we report genome-scale CRISPR interference screening using 41,939 guide RNAs designed from the E. limosum genome, one of the model acetogenic species, where all genes were targeted for tran-scriptional suppression. We investigated the fitness contributions of 96% of the total genes identified, revealing the gene fitness and essentiality for heterotrophic and auto-trophic metabolisms. Our data show that the Wood-Ljungdahl pathway, membrane regeneration, membrane protein biosynthesis, and butyrate synthesis are essential for autotrophic acetogenesis in E. limosum. Furthermore, we discovered genes that are repression targets that unbiasedly increased autotrophic growth rates fourfold and ace-toin production 1.5-fold compared to the wild-type strain under CO2-H2 conditions. These results provide insight for understanding acetogenic metabolism and genome engineering in acetogenic bacteria.

Automated summary

Acetogenic bacteria have potential in sustainable bioconversion of carbon oxides into biochemicals. Through genome-scale CRISPR interference screening, we identified the fitness contributions of 96% of the genes in E. limosum, revealing the essentiality of certain pathways for autotrophic acetogenesis. We also discovered repression target genes that improved autotrophic growth rates and acetoin production.