Biology subjects

Shmidov, E.

Publications and source records attributed to Shmidov, E..

2 recordsLinked to original sources

bioRxiv2026

CBASS limits bacteriophage production while maintaining cell viability in Pseudomonas aeruginosa

CBASS is an immune pathway that recognizes phage infection and generates cyclic nucleotide signals, which directly activate effectors that stop phage replication. Membrane-acting effectors are proposed to induce cell death to prevent phage replication; however, this mechanism has not been assessed with endogenous expression levels of the effector. We therefore sought to determine the cell viability outcomes of the CBASS phospholipase effector (CapV) upon activation with 3,3-cGAMP signals in Pseudomonas aeruginosa. Here, we surprisingly observe that constitutive 3,3-cGAMP signaling from the synthase (CdnA) enables robust cell growth and viability while effectively abolishing phage production in a CapV-dependent manner. Exogenous 3,3-cGAMP also enhances CBASS anti-phage activity and cell growth. Moreover, constitutive activation of the CapV effector induces no cell fitness cost, and blocks replication of many, but not all, phages. This demonstrates that a cyclic nucleotide-activated CBASS effector possess a degree of phage specificity that has been previously overlooked. When CBASS is active, phage transcription and initiation of DNA replication proceed normally, but phages do not reach maximum DNA levels and fewer mature virions are produced. Based on these findings, we propose that CapV interferes with the early stages of phage capsid assembly at the cell membrane and resultantly disrupts DNA packaging. Collectively, we demonstrate that a successful CBASS response antagonizes a late-stage of the phage replication cycle while maintaining cell viability.

microbiology↗

bioRxiv2024

Multigenerational Proteolytic Inactivation of Restriction Upon Subtle Genomic Hypomethylation

Restriction-modification (R-M) systems, present in most bacterial genomes, protect against phage infection by detecting and degrading invading foreign DNA. However, like many prokaryotic anti-phage systems, R-M systems pose a significant risk of auto-immunity, exacerbated by the presence of hundreds to thousands of potential cleavage sites in the bacterial genome. In Pseudomonas aeruginosa, restriction inactivation upon growth at high temperatures was previously described, however, which system is being inactivated, the underlying mechanism, as well as the timing of recovery, remain unknown. Here, we report that P. aeruginosa Type I methyltransferase (HsdMS) and restriction endonuclease (HsdR) components are degraded by two Lon-like proteases when replicating above 41 {degrees}C, which induces partial genome hypomethylation and simultaneously prevents self-targeting, respectively. Interestingly, upon return to 37 {degrees}C, methyltransferase activity returns gradually, with restriction activity not fully recovering for over 60 bacterial generations, representing the longest bacterial memory to our knowledge. Forced expression of HsdR over the first 45 generations is toxic, demonstrating the fitness benefit of HsdR inactivation. Our findings demonstrate that type I R-M is tightly regulated post-translationally with a remarkable memory effect to ensure genomic stability and emphasize the importance of mitigating auto-toxicity for bacterial defense systems.

microbiology↗