The bacterium Xenorhabdus nematophila is an insect pathogen that produces several proteins that enable it to kill insects. Screening of a cosmid library constructed from X. nematophila strain A24 identified a gene that encoded a novel protein that was toxic to insects. The 42-kDa protein encoded by the toxin gene was expressed and purified from a recombinant system, and was shown to kill the larvae of insects such as Galleria mellonella and Helicoverpa armigera when injected at doses of around 30 -40 ng/g larvae. Sequencing and bioinformatic analysis suggested that the toxin was a novel protein, and that it was likely to be part of a genomic island involved in pathogenicity. When the native bacteria were grown under laboratory conditions, a soluble form of the 42-kDa toxin was secreted only by bacteria in the phase II state. Preliminary histological analysis of larvae injected with recombinant protein suggested that the toxin primarily acted on the midgut of the insect. Finally, some of the common strategies used by the bacterial pathogens of insects, animals, and plants are discussed.
Xenorhabdus and Photorhabdus are gram-negative bacteria that produce a range of proteins that are toxic to insects. We recently identified a novel 42-kDa protein from Xenorhabdus nematophila that was lethal to the larvae of insects such as Galleria mellonella and Helicoverpa armigera when it was injected at doses of 30 to 40 ng/g larvae. In the present work, the toxin gene txp40 was identified in another 59 strains of Xenorhabdus and Photorhabdus, indicating that it is both highly conserved and widespread among these bacteria. Recombinant toxin protein was shown to be active against a variety of insect species by direct injection into the larvae of the lepidopteran species G. mellonella, H. armigera, and Plodia interpunctella and the dipteran species Lucilia cuprina. The protein exhibited significant cytotoxicity against two dipteran cell lines and two lepidopteran cell lines but not against a mammalian cell line. Histological data from H. armigera larvae into which the toxin was injected suggested that the primary site of action of the toxin is the midgut, although some damage to the fat body was also observed.
Eleven Australian natural populations of Drosophila melanogaster were screened by electrophoresis for evidence of null and/or low activity variants at the Gdph locus. Of 5018 alleles investigated, 57 had markedly lower GPDH activity, as judged by their heterozygous phenotypes, than control alleles. GPDH assays of 13 of these variant alleles showed that whilst they were heterogeneous in their properties and included electrophoretic variants and two categories of low-activity variant, there were no true null alleles. The most common low-activity variants exhibited dominance for GPDH activity in heterozygotes with normal alleles, and were shown to share this property with an allele previously isolated from a London (UK) population (Langley etal., 1981).
Two second chromosomes (H31 and T198) which when homozygous give relatively low a glycerol-3-phosphate dehydrogenase (GPDH) activity have been isolated from natural populations of Drosophila melanogaster. In heterozygotes between H31 and T198 and chromosomes bearing standard Gpdh alleles there is dominance for GPDH activity and for the amount of GPDH protein. The increased level of activity in the heterozygotes appears to be due to the differential expression of the standard alleles rather than to increased heterodimer activity. Recombination analyses have shown that if the effect is due to a modifier it must be less than OO4 cM from the Gpdh locus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.