Peter Lüthy

Bacillus thuringiensis toxin inhibits K+‐gradient‐dependent amino acid transport across the brush border membrane of Pieris brassicae midgut cells

The luminal membrane of larval midgut cells is the site of action of insecticidal delta‐endotoxin from Bacillus thuringiensis. At concentrations that correspond to normal effective doses in vivo, the toxin inhibits the uptake of amino acids by brush border membrane vesicles prepared from midguts of Pieris brassicae larvae. The toxin does not interact with the K+‐amino acid symport but rather increases the K+ permeability of the membrane. The toxin does not increase the permeability of lepidopteran midgut brush border membrane to either Na+ or H+ nor does it increase the K+ permeability of brush border membrane vesicles prepared from mammalian small intestine,

Pathogenesis of Bacillus thuringiensis toxins

The mode of action, and hence the histopathological events of all the δ-endotoxins produced as secondary metabolites by the species Bacillus thuringiensis are identical. The protein particles produced during the sporulation process have to be ingested by the target insects. In the intestine they are dissolved and undergo activation by gut juice proteinases. Following receptor mediated binding pores are formed leading to the loss of normal membrane function. The gut epithelial cells swell. Microvilli and other cell organelles are distorted along with the formation of vacuoles. The pathogenesis, the site and mode of action, is unique for an insecticidal metabolite. The process involved in the pathogenesis explains the specificity and the high level of safety of Bt products. The possible origin of the δ-endotoxin, reflecting a close connection between the target insects and the bacterium is discussed.

Serological relationship between three varieties of Bacillus popilliae

Abstract The serological relationship between three varieties of Bacillus popilliae was investigated by double diffusion and immunoelectrophoresis, using antigens prepared from homogenized vegetative cells in the logarithmic growth phase. The results showed the existence of a close serological relationship among the three varieties in agreement with a recently proposed taxonomic scheme for the milky disease bacteria ( Wyss, 1971 ).

Chalky disease, a bacterial septicemia of the cicada Okanagana rimosa Say☆

Abstract A disease of the cicada Okanagana rimosa Say caused by a nonsporeforming bacterium is described. A chalky-white color of the extremities and thorax is the most obvious sign of the disease. The natural prevalence has been calculated at 0.1%. The pathogen has been isolated, its morphology has been described, and attempts at in vitro culturing were successful. The close relationship of the pathogen to the family of the Corynebacteriaceae and especially to the genera Corynebacterium and Arthrobacter is discussed.