Serratia proteamaculans Strain AGR96X Encodes an Antifeeding Prophage (Tailocin) with Activity against Grass Grub (Costelytra giveni) and Manuka Beetle (Pyronota Species) Larvae.

A highly virulent strain, AGR96X, exhibiting specific pathogenicity against larvae of the New Zealand grass grub (; Coleoptera: Scarabaeidae) and the New Zealand manuka beetle ( and ; Coleoptera: Scarabaeidae), was isolated from a diseased grass grub larva. A 12-day median lethal dose of 4.89 × 10 ± 0.92 × 10 cells per grass grub larva was defined for AGR96X, and death occurred within 5 to 12 days following the ingestion of a high bacterial dose. During the infection period, the bacterium rapidly multiplied within the insect host and invaded the hemocoel, leading to a mean bacterial load of 8.2 × 10 cells per larva at 6 days postingestion. Genome sequencing of strain AGR96X revealed the presence of a variant of the antifeeding prophage (Afp), a tailocin designated AfpX. Unlike Afp, AfpX contains two Afp16 tail-length termination protein orthologs and two putative toxin components. A 37-kb DNA fragment encoding the AfpX-associated region was cloned, transformed into , and fed to and larvae, causing mortality. In addition, the deletion of the putative chaperone component abolished the virulence of AGR96X. Unlike Afp, the AfpX tailocin could be induced by mitomycin C. Transmission electron microscopy analysis revealed the presence of Afp-like particles of various lengths, and when the purified AfpX tailocin was fed to grass grub or manuka beetle larvae, they underwent phenotypic changes similar to those of larvae fed AGR96X. strain AGR96X shows dual activity against larvae of endemic New Zealand pasture pests, the grass grub () and the manuka beetle ( spp.). Unlike , the causal agent of amber disease, which takes 3 to 4 months to kill grass grub larvae, AGR96X causes mortality within 5 to 12 days of ingestion and invades the insect hemocoel. AGR96X produces a unique variant of the antifeeding prophage (Afp), a cell-free phage-like entity that is proposed to deliver protein toxins to the grass grub target site, causing a cessation of feeding activity. Unlike other Afp variants, AGR96X Afp, named AfpX, contains two tail-length termination proteins, resulting in greater variability in the AfpX length. AfpX shows dual activity against both grass grub and manuka beetle larvae. AGR96X is a viable alternative to for pest control in New Zealand pasture systems.