Serratia entomophila and Serratia proteamaculans cause amber disease in the grass grub Costelytra zealandica (Coleoptera: Scarabaeidae), an important pasture pest in New Zealand. Larval disease symptoms include cessation of feeding, clearance of the gut, amber coloration, and eventual death. A 115-kb plasmid, pADAP, identified in S. entomophila is required for disease causation and, when introduced into Escherichia coli , enables that organism to cause amber disease. A 23-kb fragment of pADAP that conferred disease-causing ability on E. coli and a pADAP-cured strain of S. entomophila was isolated. Using insertion mutagenesis, the pathogenicity determinants were mapped to a 17-kb region of the clone. Sequence analysis of the 17-kb region showed that the predicted products of three of the open reading frames ( sepA , sepB , and sepC ) showed significant sequence similarity to components of the insecticidal toxin produced by the bacterium Photorhabdus luminescens . Transposon insertions in sepA , sepB , or sepC completely abolished both gut clearance and cessation of feeding on the 23-kb clone; when recombined back into pADAP, they abolished gut clearance but not cessation of feeding. These results suggest that SepA, SepB, and SepC together are sufficient for amber disease causation by S. entomophila and that another locus also able to exert a cessation-of-feeding effect is encoded elsewhere on pADAP.

Serratia entomophilaandSerratia proteamaculans(Enterobacteriaceae) cause amber disease in the grass grubCostelytra zealandica(Coleoptera: Scarabaeidae), an important pasture pest in New Zealand. Larval disease symptoms include cessation of feeding, clearance of the gut, amber coloration, and eventual death. A 155-kb plasmid, pADAP, carries the genessepA,sepB, andsepC, which are essential for production of amber disease symptoms. Transposon insertions in any of thesepgenes in pADAP abolish gut clearance but not cessation of feeding, indicating the presence of an antifeeding gene(s) elsewhere on pADAP. Based on deletion analysis of pADAP and subsequent sequence data, a 47-kb clone was constructed, which when placed in either anEscherichia colior aSerratiabackground exerted strong antifeeding activity and often led to rapid death of the infected grass grub larvae. Sequence data show that the antifeeding component is part of a large gene cluster that may form a defective prophage and that six potential members of this prophage are present inPhotorhabdus luminescenssubsp.laumondiiTTO1, a species which also hassepgene homologues.

A Gram-negative, rod-shaped, non-spore-forming bacterium (MH96^T) was isolated from diseased larvae of the New Zealand grass grub,Costelytra zealandica(Coleoptera: Scarabaeidae). On the basis of 16S rRNA gene sequence similarity, strain MH96^Tis a member of the genusYersinia, which is a member of the classGammaproteobacteria. The most similar 16S rRNA gene sequence to that of MH96^Tis that of the type strain ofYersinia mollaretii(98.5 % similarity) followed by those of the type strains ofYersinia aldovae,Y. frederikseniiandY. rohdei(all 98.4 % similarity). Multilocus sequence typing of five housekeeping genes (dnaJ,glnA,gyrB,groELandrecA) identifiedYersinia ruckeri(81–92 % similarity) as the closest relative. The results of DNA–DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain MH96^Tfrom the four most closely relatedYersiniaspecies with validly published names, including aY. ruckeriisolate. Strain MH96^Ttherefore represents a novel species, for which the nameYersinia entomophagasp. nov. is proposed, with the type strain MH96^T( = DSM 22339^T = ATCC BAA-1678^T).

Toxin complex (Tc) proteins are a class of bacterial protein toxins that form large, multisubunit complexes. Comprising TcA, B, and C components, they are of great interest because many exhibit potent insecticidal activity. Here we report the structure of a novel Tc, Yen-Tc, isolated from the bacterium Yersinia entomophaga MH96, which differs from the majority of bacterially derived Tcs in that it exhibits oral activity toward a broad range of insect pests, including the diamondback moth ( Plutella xylostella ). We have determined the structure of the Yen-Tc using single particle electron microscopy and studied its mechanism of toxicity by comparative analyses of two variants of the complex exhibiting different toxicity profiles. We show that the A subunits form the basis of a fivefold symmetric assembly that differs substantially in structure and subunit arrangement from its most well characterized homologue, the Xenorhabdus nematophila toxin XptA1. Histopathological and quantitative dose response analyses identify the B and C subunits, which map to a single, surface-accessible region of the structure, as the sole determinants of toxicity. Finally, we show that the assembled Yen-Tc has endochitinase activity and attribute this to putative chitinase subunits that decorate the surface of the TcA scaffold, an observation that may explain the oral toxicity associated with the complex.

The Serratia entomophila antifeeding prophage (Afp) is thought to form a virus-like structure that has activity towards the New Zealand grass grub, C