Purification and characterization of the chitosanase from Aeromonas sp HG08

In this work, the characterization of a chitosanase-producing bacterium isolated from soil was reported and this strain was grouped under the genus Aeromonas by virtue of its morphological, physiological properties and 16S rDNA gene sequences. It is the first report that the genus Aeromonas could produce chitosanase. Aeromonas sp. HG08 could secrete the chitosanase ( named AsChi) with molecular weight of 70 kDa. The optimum pH and temperature of AsChi was 6.0 and 55 degrees C, respectively. The activity of AsChi was markedly enhanced by Mn2+ and inhibited by Fe3+, Cu2+, Ag+ and Hg2+; additionally, the activity of AsChi was increased with the degree of deacetylation ( DDA) of chitosan. Through viscosimetric assay, AsChi probably hydrolyzed chitosan in an endo-type fashion.

Identification and characterization of a virulence-associated protease from a pathogenic Pseudomonas fluorescens strain

Pseudomonas fluorescens is an aquaculture pathogen that can infect a number of fish species. The virulence mechanisms of aquatic P. fluorescens remain largely unknown. Many P. fluorescens strains are able to secrete an extracellular protease called AprX, yet no AprX-like proteins have been identified in pathogenic P. fluorescens associated with aquaculture. In this study, a gene encoding an AprX homologue was cloned from TSS, a pathogenic A fluorescens strain isolated from diseased fish. In TSS, AprX is secreted into the extracellular milieu, and the production of AprX is controlled by growth phase and calcium. Mutation of aprX has multiple effects, which include impaired abilities in interaction with cultured host cells, adherence to host mucus, modulation of host immune response, and dissemination and survival in host tissues and blood. Purified recombinant AprX exhibits apparent proteolytic activity, which is optimal at pH 8.0 and 50 degrees C. The protease activity of recombinant AprX is enhanced by Ca2+ and Zn2+ and reduced by Co2+. Cytotoxicity analyses showed that purified recombinant AprX has profound toxic effect on cultured fish cells. These results demonstrate that AprX is an extracellular metalloprotease that is involved in bacterial virulence. (C) 2009 Elsevier B.V. All rights reserved.

Toxicity and protective efficiency of cryoprotectants to flounder (Paralichthys olivaceus) embryos

With the purpose of finding an ideal cryoprotectant or combination of cryoprotectants in a suitable concentration for flounder (Paralichthys olivaceus) embryo cryopreservation, we tested the toxicities, at culture temperature (16 degrees C), of five most commonly used cryoprotectants-dimethyl sulfoxide (Me2SO), glycerol, methanol (MeOH), 1,2-propylene glycol (PG) and ethylene glycol (EG). In addition, cryoprotective efficiency to flounder embryos of individual and combined cryoprotectants were tested at -15 degrees C for 60 min. Five different concentrations of each of the five cryoprotectants and 20 different combinations of these cryoprotectants were tested for their protective efficiency. The results showed that the toxicity to flounder embryos of the five cryoprotectants are in the following sequence: PG < MeOH < Me2SO < glycerol < EG (P < 0.05); whereas the protective efficiency of each cryoprotectant, at -15 degrees C for a period of 60 min, are in the following sequence: PG > Me2SO approximate to MeOH approximate to glycerol > EG (greater symbols mean P < 0.05, and approximate symbols mean P > 0.05). Methanol combined with any one of the other cryoprotectants gave the best protection, while ethylene glycol combined with any one of the other cryoprotectants gave the poorest protection at -15 degrees C. Toxicity effect was concentration dependent with the lowest concentration being the least toxic for all five cryoprotectants at 16 degrees C. For PG, MeOH and glycerol, 20% solutions gave the best protection at -15 degrees C; whereas a 15% solution of Me2SO, and a 10% solution of EG, gave the best protection at -15 degrees C. (c) 2004 Elsevier Inc. All rights reserved.

Integrated cultivation of the red alga Kappaphycus alvarezii and the pearl oyster Pinctada martensi

The effect of simultaneously cultivating the pearl oyster Pinctada martensi and the red alga Kappaphycus alvarezii on growth rates of both species was investigated in laboratory and field studies conducted from December 1993 to June 1995. The two study sites were in subtidal areas 100 km apart off the east coast of Hainan Island, China. Pearl oysters were cultivated in the center of an algal farm and red alga was cultivated in the center of the pearl oyster farm. These field experiments showed higher growth rates of both P. martensi and K. alvarezii in a co-culture system than in a monospecies culture system. Laboratory studies showed that the algae removed nitrogenous wastes released by pearl oysters. Algae treated with pearl oyster wastes grew much faster than those without oyster wastes. Algae treated with the seawater to which NH4Cl, NaNO3 and NaNO2 were added grew at the same rate as those treated with natural seawater containing oyster nitrogenous wastes, suggesting that enhanced growth of algae in the co-culture system was largely due to nitrogenous metabolites of the pearl oysters. In the co-culture, growth of pearl oysters was positively influenced by the presence of rapidly growing algae but when seawater temperature decreased below 20 degrees C, the algae grew slowly and there was no measurable benefit of mixed culture to either algae or pearl oyster.