W.A. Shipton

Bacterial flora from the gut of the wild and cultured banana prawn, Penaeus merguiensis

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.

Effect of Bioremediation on the Microbial Community in Oiled Mangrove Sediments

Bioremediation was conducted in the field on a mature Rhizophora stylosa mangrove stand on land to be reclaimed near Fishermans Landing Wharf, Gladstone Australia. Gippsland crude oil was added to six large plots (>40 m(2)) and three plots were left untreated as controls. Bioremediation was used to treat three oiled plots and the remaining three were maintained as oiled only plots. The bioremediation strategy consisted of actively aerating the sediment and adding a slow-release fertilizer in order to promote oil biodegradation by indigenous micro-organisms. Oil addition stimulated the numbers of alkane-degrading bacteria slightly to levels of 10(4)-10(5)/g sediment. Bioremediation of the oiled sediment had a marked effect on the alkane-degrading population, increasing the population size by three orders of magnitude from 10(5) to 10(8) cells/g of sediment. An effect of bioremediation on the growth of aromatic-degraders was detected with numbers of aromatic-degraders increasing from 10(4) to 10(6) cells/g of sediment. Active aeration and nutrient addition significantly stimulated the growth of hydrocarbon-degraders in oiled mangrove sediment in the field

Survival of Aedes aegypti (Diptera: Culicidae) Eggs in Surface and Subterranean Breeding Sites During the Northern Queensland Dry Season

Abstract 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.

Arbuscular mycorrhizas and ectomycorrhizas on Eucalyptus grandis (Myrtaceae) trees and seedlings in native forests of tropical north-eastern Australia

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.

Environmental Attributes Influencing the Distribution of Burkholderia pseudomallei in Northern Australia.

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.

Extension of banana shelf life

Disease severity in banana fruit was significantly reduced by hot water treatment (50 ± 2°C for 5 min) and fungicide application (prochloraz 250 ppm), and the latter treatment also reduced disease incidence. Fruits stored at low temperatures (10, 14 and 18°C) exhibited similar disease severity levels throughout the period of investigation and at levels much lower than those observed in fruits held at room temperature. At the 25th day of storage, the highest disease severity (61.8%) occurred in the untreated fruits at room temperature, whereas the fruits treated with fungicide and hot water showed remarkably small areas of the fruit covered by disease (< 3.4%). Colletotrichum musae, responsible for the most important postharvest disease known as anthracnose, was the most abundant pathogen isolated. Fruit dipped in hot water developed desirable colour and firmness characteristics, as did the fungicide-treated fruits. The former treatment provides an alternative for those wishing to minimise the use of chemicals in order to achieve market place appeal.

Spontaneous fermentation of traditional sago starch in Papua New Guinea.

Sago starch is an important dietary carbohydrate in lowland Papua New Guinea (PNG). An investigation was conducted to determine whether microbes play a role in its preservation using traditional methods. In 12 stored sago samples collected from PNG villages, lactic acid bacteria (LAB) were present (> or = 3.6 x 10(4)cfu/g) and pH ranged from 6.8 to 4.2. Acetic and propionic acids were detected in all samples, while butyric, lactic and valeric acids were present in six or more. In freshly prepared sago, held in sealed containers in the laboratory at 30 degrees C, spontaneous fermentation by endogenous microflora of sago starch was observed. This was evident by increasing concentrations of acetic, butyric and lactic acids over 4 weeks, and pH reducing from 4.9 to 3.1: both LAB and yeasts were involved. Survival of potential bacterial pathogens was monitored by seeding sago starch with approximately 10(4)/g of selected organisms. Numbers of Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus fell to < 30/g within 7 days. Salmonella sp. was present only in low numbers after 7 days (< 36/g), but Escherichia coli was still detectable after three weeks (> 10(2)/g). Fermentation appeared to increase the storability and safety of the product.

Mycotoxins and toxigenic fungi in sago starch from Papua New Guinea

Aims:  To assay sago starch from Papua New Guinea (PNG) for important mycotoxins and to test fungal isolates from sago for mycotoxin production in culture.

Bacterial contamination of sago starch in Papua New Guinea

Sago starch is an important food in lowland Papua New Guinea. Extraction of the starch from the palm and storage were performed by way of traditional methods that have been used for thousands of years. Currently, very little is known about the microbiology of sago starch. Sago samples were collected from areas of high starch utilization and analyzed for the presence of bacterial pathogens and indicator organisms. Storage methods and duration were recorded at the time of collection, and pH and water activity on arrival at the laboratory. Sago starch was found to harbor high levels of fecal contamination, as well as various food pathogens including Salmonella, Bacillus cereus, and coagulase-positive staphylococci. Clostridium perfringens was only present infrequently in samples and in very low numbers, while Listeria monocytogenes was not isolated from sago starch. The presence of high levels of fecal contamination in sago starch is of particular concern, and may contribute to diarrheal disease in rural Papua New Guinea.

Effects of phosphorus supply on in vitro growth and phosphatase activity of Frankia isolates from Casuarina

An in vitro experiment was conducted to investigate the effects of different sources and levels of P supply on growth, viability and phosphatase activity of three tropical Frankia strains isolated from Casuarina. P concentration for optimum growth was between 0.1 and 10.0 μM in the absence of external combined nitrogen. Specific viability was not influenced by P supply. Morphological features of Frankia, such as hyphal length and vesicle numbers, were found to largely mirror growth. Phosphatase activity was detected in all three Frankia strains and was highest when P was omitted from the culture solution. There were more than 10-fold differences between the Frankia strains in the level of phosphatase activities shown. This study suggested that soils low in P are unlikely to restrict micro-symbiont growth activity.