Engineering synthetic genetic circuits distributed among multiple bacteria has the potential to enable novel applications of microbial consortia, from bioproduction to environmental and health applications. In this work, bacterial transcriptional logic gates and cell-cell communication channels (i.e. sensors and signal biosynthesis) were constructed as a foundation for developing interphylum distributed genetic circuits. Using repressors from the TetR family and sets of synthetic designed promoters, we constructed and characterized libraries of 13 NOT and 7 NOR gates to generate building blocks for genetic circuits in Bacillus subtilis, an industrially relevant, model Gram-positive soil bacterium. Further, a synthetic communication channel was established between Escherichia coli and B. subtilis using homoserine lactone (HSL) signaling molecules, wherein E. coli enzymatically produces the HSL signal and B. subtilis detects and responds to it using synthetic HSL sensors. This system provides a framework for interspecies coordination of gene expression for these bacteria. Future work will focus on expanding the library of genetic circuit building blocks and extending interspecies communication to additional bacteria, such as other members of the bacterial phylum Pseudomonadota, which includes other metabolically versatile soil bacteria. These efforts will contribute to the broader goal of designing engineered microbial communities with precisely controlled interactions for diverse biotechnological applications.
