Combined influences of particulate and dissolved factors in the toxicity of Microcystis aeruginosa (NRC-SS-17) to the rotifer Brachionus calyciflorus

The rotifer Brachionus calyciflorus is subject to the combined influence of particulate and dissolved factors derived from the toxic cyanobacterium Microcystis aeruginosa. Toxicity manifests itself through reduction of cohort survivorship and probably though reduction of cohort reproduction. Toxic effects are seen only when there is a particulate food material available in suspension, either M. aeruginosa itself or another food type which may act as a carrier for a dissolved toxic factor. Regardless of exact mechanism, the presence of a toxic strain of this blue-green may lead to diminution of population growth of co-occurring rotifer populations.     

Mutation accumulation in populations of varying size: large effect mutations cause most mutational decline in the rotifer Brachionus calyciflorus under UV‐C radiation

Theory predicts that fitness decline via mutation accumulation will depend on population size, but there are only a few direct tests of this key idea. To gain a qualitative understanding of the fitness effect of new mutations, we performed a mutation accumulation experiment with the facultative sexual rotifer Brachionus calyciflorus at six different population sizes under UV‐C radiation. Lifetime reproduction assays conducted after ten and sixteen UV‐C radiations showed that while small populations lost fitness, fitness losses diminished rapidly with increasing population size. Populations kept as low as 10 individuals were able to maintain fitness close to the nonmutagenized populations throughout the experiment indicating that selection was able to remove the majority of large effect mutations in small populations. Although our results also seem to imply that small populations are effectively immune to mutational decay, we caution against this interpretation. Given sufficient time, populations of moderate to large size can experience declines in fitness from accumulating weakly deleterious mutations as demonstrated by fitness estimates from simulations and, tentatively, from a long‐term experiment with populations of moderate size. There is mounting evidence to suggest that mutational distributions contain a heavier tail of large effects. Our results suggest that this is also true when the mutational spectrum is altered by UV radiation.     

A gradient of interstitial Niphargus rhenorhodanensis populations in two karst/floodplain transition zones of the French Jura

The Bou-Rouch technique was used to sample two small alluvial plains in two different karst areas. One was mainly supplied by karst water (Verna), the other by both karst and surface water (Pissoir).Physical and chemical characteristics varied with time (seasons) and location of sampling sites at both stations.The distribution of Niphargus rhenorhodanensis populations was influenced by the geographical characteristics of the outlets. Only a small number of individuals was found near the outlet and none in the floodplain when the outlet was located at a base-level (Verna). Individuals were more numerous and their presence constant at all sites and dates when the outlet was located at the overflow level of the massif (Pissoir).     

Development of an automated water toxicity biosensor using Thiobacillus ferrooxidans for monitoring cyanides in natural water for a water filtering plant

An on-line biosensor consisting of immobilized Thiobacillus ferrooxidans and an oxygen electrode was developed for automated monitoring of acute toxicity in water samples. T. ferrooxidans is an obligatory acidophilic, autotrophic bacterium and derives its energy by the oxidation of ferrous ion, elemental sulfur, and reduced sulfur compounds including metal sulfides. The assay is based on the monitoring of a current increase by addition of toxicoids, which is caused by the inhibition of bacterial respiration and decrease in oxygen consumption. Optimum cell number on the membrane was 5.0 x 10(8) cells. The steady-state current was obtained when concentration of FeSO4 was above 3.6 mM at pH 3. The sensor response of T. ferrooxidans immobilized membrane for 5.0 microM KCN was within an error of 10% for 30 membranes. A linear relationship was obtained at KCN concentration in the range of 0.5-3.0 microM in a flow-type monitoring system. Minimum detectable concentrations of KCN, Na2S, and NaN3 were 0.5, 1.2, and 0.07 microM, respectively. The monitoring system contained two biosensors and these sensors were cleaned with sulfuric acid (pH 1.5) twice a day. This treatment could remove fouling on microbial immobilized membrane by natural water and ferrous precipitation in the flow cell. This flow-type monitoring sensor was operated continuously for 5 months. Also, T. ferrooxidans immobilized membrane can be stored for one month at 4 degrees C when preserved with wet absorbent cotton under argon gas.