Operation CRISPR: Deploying precision guided tools to target unique species in a complex microbiome

In microbial communities, bacterial populations are commonly controlled using indiscriminate, broad range antibiotics. There are few ways to target specific strains effectively without disrupting the entire microbiome and local environment. The goal of our project is to take advantage of a natural horizontal gene transfer mechanism in bacteria to precisely affect gene expression in selected strains. We combine bacterial conjugation with CRISPRi, an RNAi-like repression system developed from bacteria, to regulate gene expression in targeted strains within a complex microbial community. One possible application is to selectively repress pathogenic genes in a microbiome, leaving the community makeup unaffected. In addition, we use CRISPRi to lay the groundwork for transferring large circuits that enable complex functionality and decision-making in cells.

In our first project, we have incorporated catalytically dead CAS9 (dCAS9) in conjunction with synthetic gRNAs complementary to pathogenic bacterial genes into a plasmid that naturally conjugates into neighboring bacterial cells. The specificity of the gRNAs will potentially allow us to target specific populations of bacterial pathogens in soil while leaving positive bacterial populations unharmed.

Our second project will provide plants with a sugar-mediated synthetic circuit that boosts a plant’s natural immune system and pesticide-producing capabilities in response to different levels of sugar a plant naturally produces in response to pests. The repression capabilities of dCAS9 will be used to regulate the synthetic circuit promoters that sense high or low sugar levels, reducing metabolic strain.