Journal Article

Induced expression of the <i>Serratia entomophila</i> Sep proteins shows activity towards the larvae of the New Zealand grass grub <i>Costelytra zealandica</i>

Mark R.H. Hurst, Sandra M. Jones, Binglin Tan and Trevor A. Jackson

in FEMS Microbiology Letters

Volume 275, issue 1, pages 160-167
Published in print October 2007 |
Published online July 2007 | e-ISSN: 1574-6968 | DOI:

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Serratia entomophila and Serratia proteamaculans cause amber disease of the grass grub Costelytra zealandica (Coleoptera: Scarabaeidae). Three genes required for virulence, sepABC, are located on a large plasmid, pADAP. The translated products of the sep genes are members of the toxin complex (Tc) family of insecticidal toxins that reside in the genomes of some Enterobacteriaceae. Each of the sep genes was placed either singly or as various combinations under the control of an inducible arabinose promoter, allowing their inductive expression. Western Immunoblot confirmed that each of the Sep proteins migrated at their predicted size on sodium dodecyl sulphate-polyacrylamide gel electrophoresis gel. Bioassays of sonicated filtrates derived from the various arabinose-induced para-SEP constructs showed that only when sepA, sepB and sepC were coexpressed were amber disease symptoms observed in grass grub larvae. Fourteen days after ingestion of the Sep protein filtrate, ∼64% of the larvae reverted from a diseased to a healthy phenotype. Redosing the revertents with a fresh Sep protein filtrate reinitiated the amber pathotype, indicating that the Sep proteins are needed to be continuously present to exert an effect.

Keywords: Sep proteins; Serratia entomophila; Costelytra zealandica; amber disease

Journal Article.  3992 words.  Illustrated.

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