PhotorhabdllS colonise the gut of insect-pathogenic nematodes, and are themselves insect pathogens that produce variety of toxicity factors. One protein, Mns, is highly conserved within the genus and constitutes over 30% of the total protein secretion from Photorhabdlls 11l11linescens, but is shown in this study not to be an insect toxin. Mns associates with extracellular material when Photorhabdlls grows in colony biofilms, and modifies the attachment of cells to surfaces. The protein is also detected in aggregations of Caenorhabditis elegans nematodes induced by Photorhabdus aSY11lbiotica supernatant, but appears not to interact with its symbiotic host nematodes, Heterorhabditis. Here, we use circular dichroism, dynamic light scattering and differential scanning calorimetry to characterise Mns, and propose that the high propensity of the protein to aggregate in vitro may relate to its function in vivo. In this report, cytochrome P450-mediated insecticide resistance in Drosophila 11lelanogaster has also been investigated. In Hikone-R flies, resistance to DDT and other insecticides is conferred by overexpression of a single cytochrome P450 gene, Cyp6gl. Here, CYP6G1 is purified from Escherichia coli as a recombinant protein, and used to prepare anti-CYP6G1 antibodies to show the expression pattern of the protein in insecticide-resistant and -susceptible flies. CYP6Gl is expressed in Hikone-R fly sperm, indicating that the protein has a role in reproduction. Furthermore, a homology model of CYP6G1 is presented, and shows not only how a variety of insecticides can be accommodated by the active site cavity, but also that the enzyme may contribute to hormone titres in the fly. How this relates to life history traits previously identified in Hikone-R flies is discussed. ii