Cm Burke

Prospects of using marine actinobacteria as probiotics in aquaculture

Chemotherapeutic agents have been banned for disease management in aquaculture systems due to the emergence of antibiotic resistance gene and enduring residual effects in the environments. Instead, microbial interventions in sustainable aquaculture have been proposed, and among them, the most popular and practical approach is the use of probiotics. A range of microorganisms have been used so far as probiotics, which include Gram-negative and Gram-positive bacteria, yeast, bacteriophages, and unicellular algae. The results are satisfactory and promising; however, to combat the latest infectious diseases, the search for a new strain for probiotics is essential. Marine actinobacteria were designated as the chemical factory a long time ago, and quite a large number of chemical substances have been isolated to date. The potent actinobacterial genera are Streptomyces; Micromonospora; and a novel, recently described genus, Salinispora. Despite the existence of all the significant features of a good probiont, actinobacteria have been hardly used as probiotics in aquaculture. However, this group of bacteria promises to supply the most potential probiotic strains in the future.

Biofouling of fish-cage netting: the efficacy of a silicone coating and the effect of netting colour

Abstract The efficacy of a silicone coating (Veridian 2000) to reduce fouling on salmon-cage netting was examined at a salmon farm in Tasmania, Australia. Significantly less fouling occurred on the white silicone-coated netting (1.9 kg/m 2 ) compared to uncoated white (7.8 kg/m 2 ) and black (8.5 kg/m 2 ) netting after 163 days immersion. On silicone-coated netting the green alga Ulva rigida dominated the fouling mass, with smaller amounts of solitary ascidians. In contrast, solitary ascidians dominated the uncoated black and white netting and accounted for more than 75% of the fouling mass. Netting colour significantly affected the growth and composition of algal fouling, but had no effect on invertebrate fouling. Cleaning experiments demonstrated that fouling organisms were poorly adhered to the silicone coating and that relatively little effort was required for their removal. Silicone coatings may provide an effective non-toxic solution to reduce fouling on sea-cages and to increase the ease of fouling removal.

The relative susceptibility of fish to infections by Flexibacter columnaris and Flexibacter maritimus

Abstract The susceptibility of freshwater and marine fish to infection by Flexibacter columnaris and Flexibacter maritimus was assessed in laboratory based experiments. Flexibactor columnaris produced a more severe disease in barramundi compared to goldfish. Both species suffered greater mortality at 25 °C than at 20 °C. Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) had similar levels of susceptibility to F. maritimus infection in seawater with approximate LC 50 values of 2.3 × 10 5 and 1.6 × 10 6 CFU mL −1 respectively. However, at salinity of 15 %. greenback flounder ( Rhombosolea tapirina ) were more resistant to F. maritimus than Atlantic salmon.

Photosynthetic bacteria in meromictic lakes and stratified fjords of the Vestfold Hills, Antarctica

Thirteen meromictic lakes and two permanently stratified fjords in the Vestfold Hills, Antarctica, were surveyed in 1983 for photosynthetic bacteria. Burton Lake and Ellis Fjord were sampled throughout the year to determine seasonal variations. Physical and chemical parameters were recorded and related to the species present. The dominant species in waters with salinities of ≤ 100.7 g kg−1 were Chlorobium vibrioforme and Chlorobium limicola with populations at the O2−H2S interface in the range 0.3 to 6.7 × 106 ml−1. Neither of these species was found at higher salinities. Thiocapsa roseopersicina and a Chromatium sp. were found in low numbers (< 105 ml−1) in most of the same waters as the Chlorobium spp. These bacterial phototrophs developed in a narrow band below the O2−H2S interface where both light and H2S were available. Very low numbers (< 102 ml−1) of Rhodopseudomonas palustris were found in both oxic and anoxic waters having salinity ≤148 g kg−1. The dominance of the Chlorobium spp. is ascribed to their more efficient maintenance metabolism during the darkness, their faster growth at low light intensities (< 1 µE m−2 s−1) and the lack of selective filtering of incident light. The Chlorobium spp. grew well at −2 °C, but not −5°C in hypersaline waters. The concentration of H2S had no apparent effect on the development of the bacterial flora. Viable cells were found to depths of 100 m in Ellis Fjord indicating that viability in total darkness could have been maintained for periods of the order of 1700 days.

Bacterial decontamination of on-grown Artemia

The bacterial load of on-grown Artemia was manipulated using a variety of commercially available enrichment DHA boosters, selected algal species (Skeletonema costatum; Nannochloropsis oculata; Tetraselmis suecica; Chaetoceros muelleri), and ozone to decontaminate enteric and external surfaces, respectively. Enrichment in C. muelleri over a 6-h period, with an additional algal exchange mid-enrichment, provided the most efficient method for enteric decontamination as measured by total viable counts. Direct exposure to ozone at 4 ppm for 5 min provided further bacterial reduction, resulting in a combined bacterial load reduction of 99.5% without compromising Artemia viability. The commercial enrichment A1 DHA Selcok (TM), containing antibacterial compounds, provides an alternative to algal-based enrichments, however, its decontaminating properties were inferior. Fluorescence in situ hybridisation (FISH) was used on occasions to verify total bacterial abundance estimates obtained by standard plating procedures. In all except one case, Johnsons Marine Agar (JMA) provided results comparable to direct counts by FISH. This indicates that the bacterial community present in on-grown Artemia cultures is dominated by several fast-growing r-strategists amenable to culture on conventional plates. Underestimation of bacterial abundance using marine agar was therefore unlikely.

The ecology of photosynthetic bacteria in Burton Lake, Vestfold Hills, Antarctica

Photosynthetic bacteria in Burton Lake, a seasonally tidal, meromictic lake of maximum depth 18 m, located in the Vestfold Hills, Antarctica, were studied throughout 1983. The dominant species were Chlorobium vibrioforme and Chlorobium limicola (up to 5.4 × 106 cells ml−1) and minor species were Thiocapsa roseopersicina (< 1.25 × 105 cells ml−1) and Rhodopseudomonas palustris (< 100 cells ml−1). The Chlorobium spp. and T. roseopersicina were found throughout the anoxic water, which ranged in temperature from −0.5°C to −2.2°C, but did not form discrete layers at the O2−H2S interface. The growth zone, however, of the Chlorobium spp. was delineated by the presence of light and H2S and was restricted to less than 3 m below the O2−H2S interface. R. palustris was found in oxic and anoxic water. Available light, which varied from 0–4.9µE m−2 s−1 at the O2−H2S interface, was considered to be the major environmental factor controlling growth of the bacterial phototrophs. Growth was initiated in spring in low light levels (< 1 µE m−2 s−1) following 3 months of darkness during winter. It is concluded that the dominance of the Chlorobium spp. was a result of their more efficient maintenance metabolism in winter and of their greater efficiency in utilizing low intensity light.

Microfouling of salmon‐cage netting: A preliminary investigation

Microfouling development on salmon‐cage netting in Tasmania, Australia, was studied by scanning electron microscopy (SEM). Temporal changes and distribution of the fouling microorganisms were documented for the horizontal netting bars in winter and spring. Diatoms were dominant on the upper surfaces of the netting bars and protista on the lower surfaces. This distribution is considered to be a consequence of shading of the lower surfaces from light and the abundance of protista is attributed to high nutrient levels associated with the dense fish population. With increasing immersion time, there was a progression in diatom communities from prostrate forms to large erect and stalked forms in winter, and tube‐dwelling forms in spring. Both the rates and the depth of fouling varied between seasons. Copper‐based and silicone‐based antifoulants effectively delayed fouling development. The former also selected for diatom species known to be copper‐tolerant. In contrast, the silicone‐treated netting was colonised...

In situ quantification of fish‐cage fouling by underwater photography and image analysis

Close‐up underwater photography and image analysis were used to quantify mesh occlusion by biofouling of salmon‐cage netting. This technique allows fast, non‐destructive sampling of cages in situ for the determination of temporal and spatial changes in fouling. The area of net blockage can be easily determined, allowing rapid evaluation of cleaning or antifouling performance.

Production, characterisation and diagnostic use of antisera to southern bluefin tuna (Thunnus maccoyii Castelnau) immunoglobulin

Sheep polyclonal antisera and one monoclonal antiserum (mAb) were prepared against purified southern bluefin tuna (Thunnus maccoyii Castelnau) immunoglobulin, and also rabbit polyclonal antisera were prepared against isolated immunoglobulin H chains. Activity and specificity were determined in immunoblots following SDS-PAGE in reducing and non-reducing conditions. In reducing conditions, the mAb and rabbit antisera reacted specifically with H chains of purified SBT Ig, and only with bands consistent with H chains in sera from other Thunnus spp. No cross-reactivity with reduced serum from any other teleost was found for the mAb, and only minimally for the rabbit antisera, but sheep antisera were less specific and reacted with bands other than those attributable to immunoglobulin. The antisera were used in serological assay development and detected the presence of infection with the blood fluke, Cardicola forsteri, a recently described pathogen of farmed southern bluefin tuna.

Benthic Microbial Production of Oxygen Supersaturates the Bottom Water of a Stratified Hypersaline Lake

Lake Hayward is a hypersaline lake that stratifies seasonally and maintains oxygen supersaturation in its bottom water for about 6 months each year. This phenomenon was found to be the result of photosynthesis by the benthic microbial communities, composed primarily of the cyanobacteria Cyanothece spp., Spirulina sp., and Oscillatoria sp. When these communities were present and the lake was stratified, the bottom water was supersaturated with oxygen (up to 370%). During illumination, the benthic microbial communities rapidly developed very high concentrations (e.g., >500 μM) of oxygen, which then diffused into the overlying water. However, while the overlying water became supersaturated, the concentration in the water was lower than in the benthic microbial communities because (1) transport across the sediment-water interface was limited by diffusion, and (2) turbulence rapidly mixed the oxygen throughout the much larger volume of the bottom water (approximately 1.5 m deep). Thus, import of oxygen by the benthic microbial communities at night proceeded more slowly than daytime export, allowing supersaturation of the bottom water to develop.