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Aims: There is growing awareness of the influence of the bacterial composition of the gut on the health and growth of the host. This study compared the bacterial flora from the digestive system of the wild and cultured prawn, Penaeus merguiensis. Methods and Results: Whole guts were dissected from wild and cultured prawns and divided into sections corresponding to the foregut, digestive gland, midgut and hindgut. Homogenates of these sections were plated onto seawater nutrient agar and the colonies identified to genus level and, in some cases, species. Quantitative and qualitative comparisons amongst gut regions for both wild and cultured prawns are presented. Conclusions: Both wild and cultured prawns supported remarkably similar bacterial floral compositions, which included members from the genera Aeromonas, Plesiomonas, Photobacterium, Pseudoalteromonas, Pseudomonas and Vibrio. Members of the genus Vibrio were quantitatively dominant. A number of Vibrio species were recovered solely from cultured prawns. Of these, Vibrio gazogenes was the most notable (numerically dominating in all but the midgut). The opportunistic pathogen V. parahaemolyticus was also recovered. Significance and Impact of the Study: The remarkable similarity of gut compositions between wild and cultured prawns, despite being drawn from very different habitats, suggests an influence of the host on the establishment of the gut flora. An understanding of host/gut floral interactions has significance in fostering conditions which promote the growth of cultivated hosts.

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The effect of a protracted dry season on the viability of Ae. aegypti (L.) eggs was examined in Townsville, northern Queensland, Australia. Eggs were placed in several different surface and subterranean larval habitats; and after four dry season months, only 1-10% of eggs remained viable in the surface and subterranean sites, respectively. Low humidity and predation by Periplaneta americana (L.) were the major causes of egg mortality in eggs in surface sites. P. americana was the most significant cause of egg predation in subterranean breeding sites but fungi, especially Penicillium citrinum Thom, covered egg batches within 15 d. Mycotoxins produced by the spores of P. citrinum are believed to have killed embryonating eggs. The high mortality rate of Ae. aegypti eggs during the dry season suggests that this survival strategy is unlikely to contribute to rapid and successful recolonization of surface sites at the end of the wet season.

Eucalypts have been shown to form both arbuscular mycorrhizas (AM) and ectomycorrhizas (ECM) in glasshouse experiments. Little is known, however, about the relative dominance of these two mycorrhiza types on individual eucalypt species across their natural range. This study examined mycorrhizal colonisation levels of Eucalyptus grandis Hill ex Maiden roots at 29 sites representing a broad range of wet sclerophyll forest types in the wet tropics of north-eastern Australia. Adult E. grandis trees sampled in situ were invariably heavily ectomycorrhizal, with 76–100% fine root length colonised (% RLC). There were comparatively low levels of AM, with typically less than 10% RLC. Seedling E. grandis grown in intact soil cores from the field sites under glasshouse conditions had lower total levels of mycorrhiza formation compared with adult trees, with more variable ECM formation (10–95% RLC) and more extensive AM formation (10–40% RLC). There were no apparent trends in mycorrhiza formation across different soil parent material, rainfall or vegetation categories used. The current research suggests that arbuscular mycorrhizas are more prominent on seedlings, whereas ectomycorrhizas predominate in adult trees of E. grandis. Possible reasons for these differences and a comparison with other studies of eucalypt mycorrhizas under natural conditions are presented.

Factors responsible for the spatial and temporal clustering of Burkholderia pseudomallei in the environment remain to be elucidated. Whilst laboratory based experiments have been performed to analyse survival of the organism in various soil types, such approaches are strongly influenced by alterations to the soil micro ecology during soil sanitisation and translocation. During the monsoonal season in Townsville, Australia, B. pseudomallei is discharged from Castle Hill (an area with a very high soil prevalence of the organism) by groundwater seeps and is washed through a nearby area where intensive sampling in the dry season has been unable to detect the organism. We undertook environmental sampling and soil and plant characterisation in both areas to ascertain physiochemical and macro-floral differences between the two sites that may affect the prevalence of B. pseudomallei. In contrast to previous studies, the presence of B. pseudomallei was correlated with a low gravimetric water content and low nutrient availability (nitrogen and sulphur) and higher exchangeable potassium in soils favouring recovery. Relatively low levels of copper, iron and zinc favoured survival. The prevalence of the organism was found to be highest under the grasses Aristida sp. and Heteropogon contortus and to a lesser extent under Melinis repens. The findings of this study indicate that a greater variety of factors influence the endemicity of melioidosis than has previously been reported, and suggest that biogeographical boundaries to the organisms’ distribution involve complex interactions.

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