Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 1996
Publication Date: N/A
Interpretive Summary: Because the southern corn rootworm beetle is one of the most serious insect pests of United States agriculture, biological control agents that could be used for its control are urgently needed. Spiroplasmas (helical wall-less bacteria) could be used for insect control if existing pathogenicity (if any) could be enhanced; introduction of toxin genes into the bacterial chromosome has been suggested for this purpose, and has been studied in our laboratory with respect to the Colorado potato beetle. In this paper, we describe a spiroplasma that was isolated from the hemolymph of the corn rootworm beetle. The ability of this spiroplasma to pass the gut barrier of the host could make it a candidate for a biocontrol toxin vector. This paper fulfills the minimal standards established by the ICSB taxonomy subcommittee for description of spiroplasma species. The paper will be of interest to entomologists working on this pest, and to bacterial taxonomists.
Spiroplasma strain DU-1, isolated from the hemolymph of the corn rootworm was serologically distinct from other Spiroplasma species, groups, and subgroups. Cells of strain DU-1 were shown by light microscopy to be helical motile filaments. Electron microscopy revealed cells bounded only by a single cytoplasmic membrane. The organism did not appear to have a sterol requirement for growth, as has been reported for several other Spiroplasma species or strains. Optimal growth occurred at 32C with a doubling time of 0.9 h; the strain multiplied at temperatures of 10C to 41C but failed to grow at 5C or 43C. Strain DU1 produced acid from glucose but hydrolyzed neither arginine nor urea. Reciprocal serologic tests, using antigens or antisera to established Spiroplasma species, groups, subgroups, and putative groups, indicated that strain DU-1 was serologically distinct. The organism has a DNA guanine + cytosine (G + C) content of 25 + 1 mol% and a genome size of 1350 kbp. Strain DU-1 is a member of a cluster of fast-growing insect associated spiroplasmas, as determined by sequence analysis of 16S rRNA. Strain DU-1 is designated the type strain (ATCC 43210) of a new species, S. diabroticae.