Genetic and electron-microscopic characterization of Rickettsiella bacteria from the manuka beetle, Pyronota setosa (Coleoptera: Scarabaeidae)

Abstract

Larvae of manuka beetles, Pyronota spp . (Coleoptera: Scarabaeidae) cause pasture damage in New Zealand by feeding on the roots of grasses. Surveys for potential biocontrol agents revealed a putative disease, expressed as whitened larvae of one of the outbreak species, Pyronota setosa. Microbial diagnosis indicated an intracoelomic, intracellular infection, and intracellular bacteria have been identified with subcellular structures characteristic of infection by Rickettsiella-like microorganisms. These bacteria were rod-shaped, often slightly bent with a mean of 628 nm in length and 220 nm in width. Numerous associated protein crystals of variable size and shape occurred within round to oval shaped “giant bodies” either singly or as clusters of smaller crystals. Molecular phylogenetic analysis based on 16S ribosomal RNA and signal recognition particle receptor (FtsY) encoding sequences demonstrates that the manuka beetle pathogen belongs to the taxonomic genus Rickettsiella. Therefore, the pathotype designation ‘ Rickettsiella pyronotae’ is proposed to refer to this organism. Moreover, genetic analysis makes it likely that – on the basis of the currently accepted organization of the genus Rickettsiella – this new pathotype should be considered a synonym of the nomenclatural type species, Rickettsiella popilliae.