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Three bacterial enrichment cultures (ECs) were isolated from the digestive tract of Pacific white shrimp Penaeus vannamei, by growing the shrimp microbial communities in a mixture of N-acyl homoserine lactone (AHL) molecules. The ECs, characterized by denaturing gradient gel electrophoresis analysis and subsequent rRNA sequencing, degraded AHL molecules in the degradation assays. Apparently, the resting cells of the ECs also degraded one of the three types of quorum-sensing signal molecules produced by Vibrio harveyi in vitro [i.e. harveyi autoinducer 1 (HAI-1)]. The most efficient AHL-degrading ECs, EC5, was tested in Brachionus experiments. EC5 degraded the V. harveyi HAI-1 autoinducer in vivo, neutralizing the negative effect of V. harveyi autoinducer 2 (AI-2) mutant, in which only the HAI-1- and CAI-1-mediated components of the quorum-sensing system are functional on the growth of Brachionus. This suggests that EC5 interferes with HAI-1-regulated metabolism in V. harveyi. These AHL-degrading ECs need to be tested in other aquatic systems for their probiotic properties, preferably in combination with specific AI-2-degrading bacteria. [ABSTRACT FROM AUTHOR]

Abstract: Axenic rotifers (Brachionus plicatilis sensu strictu, clone 10) were obtained by treating amictic eggs with glutaraldehyde. Depending of the batch of rotifers, total disinfection could be obtained by exposure to 50–100 ppm from 1 to 2 h at 28 °C. The hatched axenic neonates were used to test the effect of microbial communities (MCs) which were isolated from either normal-performing or crashed rotifer cultures. These MCs were either used directly or were first regrown on Marine Agar. MCs were introduced to gnotobiotic Brachionus cultures in combination with three different food types, i.e. Chlorella, wild-type yeast and the mnn9 yeast mutant, which is deficient in cell wall-bound mannoprotein. In the absence of MCs or when heat-killed MCs were added, Chlorella was always the best food, while lower growth rates were observed with wild-type yeast and the mnn9 mutant as food. In the presence of live MCs and when rotifers were fed with Chlorella, the added MCs had no effect on rotifer performance. When yeasts were used as major food, all the tested MCs were able to increase the rotifer growth rate. The experiments with heat-killed MCs yielded no increase in rotifer growth rate, suggesting that the observed enhancement in rotifer growth rate was truly a probiotic effect rather than a nutritional effect. The results of this study demonstrate that gnotobiotic rotifer cultures obtained from axenic amictic eggs can be used as a test system for studying microbial-attributed as well as nutritional functions in the aquatic food chain. In addition, since the MCs originating from the crashed rotifer cultures did not decrease the growth rate in the tested rotifer cultures, it is likely that the observed crashes were not due to the presence of a standing deleterious MC. [Copyright &y& Elsevier]

Aquatic ecosystems are used for extensive rice-shrimp culture where the available water alternates seasonally between fresh and saline. Poor water quality has been implicated as a risk factor for shrimp survival; however, links between shrimp, water quality and their main food source, the natural aquatic biota inhabiting these ponds, are less well understood. We examined the aquatic biota and water quality of three ponds over an entire year in the Mekong Delta, Vietnam, where the growing season for the marine shrimp Penaeus monodon has been extended into the wet season, when waters freshen. The survival (30–41%) and total areal biomass (350–531 kg ha−1) of shrimp was constrained by poor water quality, with water temperatures, salinity and dissolved oxygen concentrations falling outside known optimal ranges for several weeks. Declines in dissolved oxygen concentration were matched by declines in both shrimp growth rates and lipid content, the latter being indicative of nutritional condition. Furthermore, as the dry season transitioned into the wet, shifts in the taxonomic composition of phytoplankton and zooplankton were accompanied by declines in the biomass of benthic algae, an important basal food source in these systems. Densities of the benthic invertebrates directly consumed by shrimp also varied substantially throughout the year. Overall, our findings suggest that the survival, condition and growth of shrimp in extensive rice-shrimp ecosystems will be constrained when poor water quality and alternating high and low salinity negatively affect the physiology, growth and composition of the natural aquatic biota. Changes in management practices, such as restricting shrimp inhabiting ponds to the dry season, may help to address these issues and improve the sustainable productivity and overall condition of these important aquatic ecosystems. Unlabelled Image • Shrimp growing is extending into the wet season in extensive rice-shrimp ponds. • Salinity, water temperature, dissolved oxygen were often suboptimal for shrimp. • Aquatic food sources declined, compositions shifted with dry-wet season transition • Shrimp survival below 50%; growth and lipid declined with dissolved oxygen • Shrimp growth, condition, survival constrained by conditions from changing salinity [ABSTRACT FROM AUTHOR]