Bacteria compete with phages in a myriad of environments for survival. This constant arms race has led to the acquisition of cyclic oligonucleotide based antiphage signaling system (CBASS) throughout all bacterial phyla. Phage infection activates CBASS which results in altruistic suicide of the host to save the clonal community, a process termed abortive infection. In Vibrio cholerae El Tor, CBASS is comprised of DncV, CapV, Vc0180, and Vc0181. DncV is activated following phage infection to synthesize 3'3'-cGAMP which activates CapV, a phospholipase that degrades the cellular membrane. Though evidence suggests VC0180 and VC0181 allow for response against broader range of phages, their function in relation to DncV remains undefined. To determine their role, we investigate the effect of VC0180 and VC0181 on the stability of DncV in vivo. During this pursuit, we discovered a novel protein which we named Bumo, for Bacterial Ubiquitin Modifier, encoded upstream of capV that is a component of the CBASS operon. We show a novel regulatory network of DncV, in which Bumo protects DncV from degradation and that VC0181 is a protease that degrades DncV. We also show evidence that VC0180 interacts with DncV. To expand our knowledge of CBASS, we also explored the function of CBASS systems encoding HNH-SAVED effectors in other Gram-negative bacteria. We discovered E. coli EDEC13E and P. fluorescens SRM1 have active CBASS systems that affect the growth capacity of heterologous hosts. We also show their nucleotide substrate specificity. Interestingly, the E. coli EDEC13E HNH-SAVED effector is inactivated following the addition of nucleotide signals, which is distinct from all previously described CBASS systems. In conclusion, Bumo is a newly discovered component of the CBASS operon that protects DncV from degradation by Vc0181. VC0180 and VC0181 both regulate DncV in separate ways. Moreover, the function of CBASS is conserved in other Gram-negative species, even though they may have adapted to respond differentially to cyclic oligonucleotide signals. The results of my thesis work lead to a better appreciation of the complexity in the regulation of CBASS signaling and the diversity in the evolution of CBASS across species.
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