Hiroto Maeda

Growth, stress tolerance and non-specific immune response of Japanese flounder Paralichthys olivaceus to probiotics in a closed recirculating system

Effects of probiotics on growth, stress tolerance and non-specific immune response in Japanese flounder Paralichthys olivaceus were evaluated in a closed recirculating system. Survival and growth of flounder treated by supplying commercial probiotics either in the diet (the probiotic diet group), or into the rearing water (the water supply group), were higher compared to the untreated group (the control group). Water quality parameters, pH, NH4−N, NO2−N and PO4−P showed lower concentration in the probiotic diet group compared with the control group and the supply group. Plasma lysozyme activity in the probiotic diet group and the water supply group was significantly higher (P<0.05) than that in the control group. In heat shock stress tests, flounder in the probiotics-treated groups showed greater heat tolerance (measured by 50% lethal time, LT50) than the control group. Pathogen challenge tests with Vibrio anguillarum (2×107 c.f.u./mL) resulted in significantly higher survival in the probiotics-treated groups than the control group. Results indicated that probiotics supplied in the rearing water and the diet of fish enhanced the stress tolerance and the non-specific immune system of Japanese flounder, providing them a higher resistance against stress conditions and pathogens.

Use of live and dead probiotic cells in tilapia Oreochromis niloticus

To investigate the effect of live and dead probiotic cells on the non-specific immune system of tilapia Oreochromis niloticus, probiotics were introduced by feeding either in the form of live or dead cells, or supplying live cells to the rearing water in a closed recirculating system. The probiotics treatment enhanced non-specific immune parameters such as lysozyme activity, migration of neutrophils and plasma bactericidal activity, resulting in improvement of resistance to Edwardsiella tarda infection. Especially, oral administration of live cells seemed to be more effective compared with other probiotic treatments such as oral administration of dead probiotic cells and supply of live probiotic cells to the rearing water. These results indicate that probiotics treatment is promising as an alternative method to antibiotics for disease prevention in aquaculture, and the viability of probiotic bacteria is a key factor to induce more potential effect of probiotics used for fish production.

Colonization and probiotic effects of lactic acid bacteria in the gut of the abalone Haliotis gigantea

Strains of lactic acid bacteria (LAB) were isolated from several different sources and evaluated in vitro for potential probiotic effects in abalones. Two isolates (Lactobacillus sp. strain a3 and Enterococcus sp. strain s6) were highly resistant to bile salt and/or gastric juice and inhibited the growth of three abalone pathogens (Listonella anguillarum, Vibrio harveyi, and V. carchariae). Each of the LAB isolates was used to supplement diet of the abalone Haliotis gigantea for a period of 3xa0weeks. One group of animals received Lactobacillus sp. strain a3 added to commercial dry feed, one group received Enterococcus sp. strain s6 added to the feed, and a control group received only standard commercial feed. Culturable LAB counts of gut homogenates indicate the a3 colonized in the gut of abalones. Digestive enzyme activities and the concentrations of a number of volatile short-chain fatty acids (VSCFA) were elevated in the gut of abalones receiving feed supplemented with the two LAB strains. These results indicate that dietary supplementation can enable LAB colonization or persistence in the gut of abalone species and can potentially enhance probiotic effects.

Effect of salinity on denitrification under limited single carbon source by Marinobacter sp. isolated from marine sediment.

Marinobacter comprises Gram‐negative, aerobic, motile, and rod‐shaped bacteria within the γ‐subclass of the Proteobacteria and is known to be halophilic or halotolerant, heterotrophic neutrophile. Two strains classified as belonging to Marinobacter, named PAD‐2 and SeT‐1, were isolated from marine sediment. The most closely related species of PAD‐2 and SeT‐1 are M. alkaliphilus and M. guinea, respectively. The strain PAD‐2 exhibited remarkably higher denitrification at concentrations of 0.5 to 1 M NaCl (3–6% w/w) than at other salinities (2 and 3 M NaCl, 12–18% w/w), and optimal denitrification was observed in media with 0.5 M NaCl. The effect of pH on denitrification by strain PAD‐2 was also examined, and the optimum denitrification occurred at neutral pH rather than under alkaline conditions. Overall, strain PAD‐2 appears to be a novel halotolerant species belonging to the genus Marinobacter that shares many characteristics, such as substrate utilization profile and optimum NaCl concentration for growth with M. alkaliphilus. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wax ester-like compounds as biosurfactants produced by Dietzia maris from n -alkane as a sole carbon source

The hydrocarbon‐degrading bacterium Dietzia maris WR‐3 was isolated from a consortium comprising ammonia‐oxidizing and denitrifying bacteria derived from marine sediments. Here, we examined biosurfactant production by strain WR‐3 when cultured using several different carbon (D‐glucose, n ‐decane, n ‐hexadecane, motor oil, olive oil, and rapeseed oil) and nitrogen (NH4)2SO4, NaNO3, yeast extract, and polypeptone) sources as growth substrates. Strain WR‐3 was able to grow and reduce the surface tension of culture broth to 31±1.0 mN m–1 when cultured using n ‐hexadecane and nitrate ions. The surface‐active compounds produced by strain WR‐3 were extracted and analyzed by thin layer chromatography. Moreover, the main components in the extract were further purified and subjected to gas chromatography/mass spectrometry (GC/MS). From the analysis, the surface‐active compounds were tentatively identified as wax ester‐like compounds, which were synthesized from the degradation process of n ‐alkane. The production of surface‐active compounds by strain WR‐3 promoted attachment of cells to hydrocarbon droplets via increased cell hydrophobicity, thus allowing enhanced degradation of water immiscible substrates. As Dietzia spp. can grow and produce wax esters from the degradation process of hydrocarbons, these marine bacteria are potentially useful for the bioremediation of hydrocarbon‐contaminated environments. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Seasonal changes in carbon and nitrogen productivity in the north basin of Lake Biwa, Japan

One o f the most significant biogeochemical processes in the euphotic layer o f freshwater environments is carbon and nitrogen production by phytoplankton assemblages. lnformation regarding the uptake of nitrogenous nutrients in freshwater lakes has recently been accumulated to elucidate its importance as a nitrogen source for phytoplankton growth and to demonstrate its significance in the biogeochemica1 nitrogen cycle (MIYAZAKI et al. 1985, WHALEN & ALEXANDER 1986, MITAMURA & SAIJO 1986a, TAKAMURA et al. 1987, BINHE & ALEXANDER 1993, PRESING et al. 1998, 2001). MITAMURA & SAIJO (1986b) measured the in situ uptake rate o f nitrogenous nutrients in the euphotic layer ofLake Biwa and demonstrated that the principal nitrogenous compounds that sustain the standing crop ofphytoplankton were arnmonia, urea and nitrate, and that phytoplankton preferentially utilized arnmonia. MITAMURA & SAuo (1986b) and MITAMURA et al. (1995) observed that relative nitrogen uptake rates by phytoplankton were ranked as arnmonia > urea > nitrate in temperate and tropical natural lakes. Several studies have reported that the regenerated forms of nitrogenous nutrients such as arnmonia and urea play significant roles as nitrogen sources for phytoplankton. To provide further information on the biogeochemical carbon and nitrogen cycling in freshwater bodies, the in situ uptake rates of arnmonia, nitrate and urea nitrogen were seasonally measured in relation to the photosynthetic carbon uptake of phytoplankton populations in the euphotic layer of the north basin of LakeBiwa.