Phages reconstitute NAD⁺ to counter bacterial immunity

Area of Science:

• Microbiology
• Virology
• Biochemistry

Background:

• Bacteria employ diverse antiphage defense systems to combat viral infections.
• Many bacterial defense systems deplete nicotinamide adenine dinucleotide (NAD+) during infection, hindering phage replication.

Purpose of the Study:

• To investigate phage strategies for overcoming bacterial NAD+-depleting defenses.
• To characterize novel phage-encoded pathways for NAD+ reconstitution.

Main Methods:

• Enzymatic assays to characterize NAD+ reconstitution pathways.
• Phylogenetic analysis of phage genomes to identify NARP genes.
• Testing phage ability to overcome bacterial defenses in vitro.

Main Results:

• Discovery of NAD+ reconstitution pathway 1 (NARP1), a two-enzyme system that regenerates NAD+ from ADP-ribose (ADPR) and nicotinamide.
• Phages encoding NARP1 successfully overcome multiple bacterial defense systems (Thoeris, DSR1, DSR2, SIR2-HerA, SEFIR).
• Identification of a second pathway, NARP2, which reconstitutes NAD+ using different metabolites.

Conclusions:

• Phages possess enzymatic pathways (NARP1 and NARP2) to counteract bacterial NAD+-depleting defenses.
• NARP1 is phage-specific, indicating a targeted viral immune evasion strategy.
• These findings reveal a novel mechanism of viral immune evasion through the reconstitution of host-depleted molecules.