The following studies were done to identify factors that influence the virulence of Xenorhabdus nematophilus and the interactions of the bacterium with the nonself defence systems of nonimmune Galleria mellonella. Isolates of X. nematophilus that are qualitatively similar in biochemical properties differed significantly in virulence for G. mellonella larvae. The production of enzymes such as proteases could not account for differences in the virulence of the isolates. / Growth conditions, influenced the growth rate and the interactions of the bacterium with nonimmune G. mellonella larvae. In general, X. nematophilus cells grown under aerobic conditions were more susceptible to the nonself defences of G. mellonella larvae than those grown under less than ideal conditions, resulting in increased clearance of the bacteria from the hemolymph (blood) of the insects. Clearance of the bacteria from the hemolymph of the insect was positively correlated with culture condition, culture age, and attachment to insect hemocytes in vitro. / Isolates of X. nematophilus produced flagella and fimbriae when grown under microaerobic and aerobic conditions. The type of fimbriae produced was influenced by culture conditions. The injection of both flagella and fimbriae in picogram quantities into nonimmune G. mellonella caused an increase in total hemocyte counts within these insect larvae. The injection of fimbrial and flagellar antigens into G. mellonella larvae caused changes in the hemocyte types found in circulation in the insect's hemolymph. (Abstract shortened by UMI.)

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Vibrio anguillarum infects many fish species in aquaculture, reducing farm productivity and negatively impacting fish welfare. Deeper understanding of the biology of V. anguillarum, particularly during infections in vivo, will help to improve disease prevention and control. Thus, the aim of this thesis was to provide further insight into the infection biology of V. anguillarum with a view to identifying better ways to reduce the impact of this pathogen in aquaculture. Conventional studies on virulence, particularly those aiming to identify novel virulence factors, often employ transposon mutagenesis where the functions of individual genes in the bacterium are disrupted. These mutant libraries are screened to identify those with attenuated virulence, allowing subsequent identification of the gene responsible. Usually the native fish host would be used but such studies are increasingly difficult to perform due to regulations on vertebrate experiments and ethical concerns. As a result, alternative invertebrate hosts are now an important means to studying microbial infections, but few models have been assessed for bacterial pathogens of fish. In this thesis, larvae of the greater wax moth Galleria mellonella were evaluated as an alternative host to investigate V. anguillarum virulence. Wild-type V. anguillarum isolates killed larvae in a dose-dependent manner, replicated in the haemolymph, and larvae infected with a lethal dose of bacteria could be rescued by antibiotic therapy, thus indicating that V. anguillarum established an infection in G. mellonella. Crucially, virulence of 11 wild-type V. anguillarum isolates correlated significantly between larva and Atlantic salmon infection models, and studies with isogenic mutants knocked out for various virulence determinants revealed conserved roles for some in larva and fish infections, including the pJM1 virulence plasmid and rtxA toxin. Thereafter, 350 strains from a V. anguillarum random transposon insertion library were screened for attenuated virulence in G. mellonella. In total, 12 strains had reduced virulence and in these mutants the transposon had inserted into genes encoding several recognised and putative virulence factors, including a haemolytic toxin (vah1) and proteins involved in iron sequestration (angB/G and angN). Importantly, the transposon in one strain had inserted into an uncharacterised hypothetical protein. Preliminary investigations found this putative novel virulence factor to contain a GlyGly-CTERM sorting domain motif, with sequence similarity to VesB of Vibrio cholerae which is involved in post-translational processing of cholera toxin. Finally, three transposon insertion libraries were mass sequenced on a MiSeq platform to identify V. anguillarum genes lacking transposon insertions. These genes were assumed to be ‘required’ for viability in the conditions under which the mutants were selected, in this case tryptone soya agar. In total, 248 genes lacked a transposon insertion and were the putative ‘required’ genes, and these may be important chemotherapeutic targets for new approaches to combat V. anguillarum infections. This thesis has furthered our understanding of the biology of the important fish pathogen V. anguillarum using an ethically acceptable approach, and the findings may assist with new ways to reduce the burden of this bacterium in aquaculture.

In recent decades, the negative effects of artificial light at night on natural ecosystems have attracted the attention of ecologists. Studies have shown that artificial light at night leads to a considerable reduction in insects and has a worrying impact on terrestrial ecosystems, including nocturnal insects (e.g. Lepidoptera) such as moths. Warm white light is generally expected to have a lower ecological impact compared with cold white light which has a higher proportion of blue light (< 500 nm). The aim of this study is to investigate the impact of three light emitting diode (LED) light sources with different spectral power distributions on the responses of the greater wax moth (Galleria mellonella) under controlled experimental settings. In this experiment, three light sources with different spectral power distribution and dark condition were used and the start response time, time active, time flap wings, time flap wings / time active, main activity area and stop area of the greater wax moth were investigated. The light treatment used were: (1) darkness (n = 13); (2) warm-white light (correlated color temperature of 2675 K, n = 12); (3) white light (4070 K, n = 4); (4) cold white light (6200 K, n = 8). The experiment was performed in a rectangular light-tight box under controlled conditions. Main activity area showed significant difference between warm-white light and cold white light. With cold white light, a larger proportion of the moths were active in the area with the highest light levels, while the main activity area in the warm white light was in the zone with the lowest light levels. Other variables, however, did not show significant differences. The conclusion is that warm white light had a lower ecological impact than cold white light due to a larger proportion of moth is attracted to areas with stronger light. The results support the notion that in outdoor environments, warm white LEDs (maximum 3000 K) should be preferred compared to cold white light LEDs (over 3000 K), to reduce the impact on insects such as moths. The low correlated color temperature light sources used outdoors deserves more in-depth development and research.