Protein alterations in Manduca sexta midgut and haemolymph following treatment with a sublethal dose of Bacillus thuringiensis crystal endotoxin

Abstract

A single sublethal dose of Bacillus thuringiensis crystal toxin was delivered to fifth instar larvae of Manduca sexta to examine the effect of the toxin on the peritrophic membrane, midgut, and haemolymph. Twelve major peptide bands, ranging in size from above 200 kd down to 24 kd, were seen in silver-stained polyacrylamide gels of control peritrophic membranes. Twenty-four hours after toxin treatment four major glycoproteins were much reduced or absent from the peritrophic membranes. Concurrently, a new 32 kd protein (PM10) appears in the peritrophic membrane. This protein is still present 72 hr after toxin treatment when the peritrophic membranes' glycoproteins have returned to control levels, and the insect has apparently recovered from the toxin. A comparison of gels of the soluble midgut proteins revealed several bands which are common to both the midgut and the peritrophic membranes. Midgut contents taken from larvae 24 hr after toxin treatment had a large number of bands which were not present in the midgut contents of control larvae. Although the protein profile of haemolymph taken from larvae 24 hr following toxin treatment was apparently unaltered from control haemolymph, 72 hr following treatment a protein band, designated M13, was induced. M13 is associated with the immune response in M. sexta. This is the first report that the proteins associated with the immune response are induced by something other than a bacterial injection.