Microbial enzyme activities as indicators of organic matter processing rates in a Lake Erie coastal wetland

1. Particulate organic material (POM) is an important source of energy and nutrients in aquatic ecosystems. The decomposition of this material is typically studied using the litter bag technique. However, this method has inherent limitations that can preclude the estimation of in situ decomposition rates, especially for fine particles. In this study, we tried to circumvent these limitations through the use of enzymatic decomposition models (EDMs), which relate mass loss rates to lignocellulase activities. With this approach, we investigated the in situ processing of three size ranges of detritus in a Typha wetland. 2. Litter was collected, dried and sorted into three size ranges [coarse (C) > 4, medium (M) 0.5–4 and fine (F) 0.063–0.5 mm] and placed in litter bags that were attached to the sediment surface at two sites in a Typha wetland in May 1994. Over a 7-month period, litter bags were collected and analysed for mass loss and the activities of six extracellular enzymes involved in the degradation of lignocellulose. In situ POM was collected concurrently, sorted into the same three size ranges and assayed for the same suite of enzymes. Additional cores were taken for the determination of organic matter standing stocks and particle size distribution. 3. Mean mass loss rates for CPOM, MPOM and FPOM were -0.139, -0.073 and -0.053% day^?1, respectively. Only CPOM rates were significantly different between sites. For CPOM and FPOM there were strong linear relationships between mass loss and cumulative enzyme activities; the mass loss data for MPOM were erratic and precluded the development of reliable enzyme models. EDMs for CPOM and FPOM were constructed from regressions relating mass loss to average cumulative lignocellulase activity, and used to estimate instantaneous in situ decomposition rates. These rates varied by site and throughout the year but averaged -0.204 and -0.045% day^?1, respectively. Based upon measurements of OM standing stock and particle size distributions, POM processing rates of 1100–1400 g m² yr^?1 were calculated. These rates are near the upper end of the range for net annual production in Typha wetlands, suggesting that there is little net accumulation of POM. 4. Despite some problems, the EDM method has the potential to facilitate studies of detrital dynamics in large, heterogeneous systems.     

An Ultrastructural and Cytochemical Study of the Cell Surface of a Suctorian Ciliate1

The surfaces of the main cell body, tentacle shaft, and knob of Discophrya collini, a freshwater suctorian ciliate, were characterized using various cytochemical techniques. Cells prepared for conventional transmission electron microscopy exhibited a 50–60 nm thick fuzzy layer over the cell body surface; this layer was absent from the tentacle knob. A thick (240 nm), two-layered surface coat surrounding the main cell body was stained with ruthenium red. This heavy coat was absent from the surface of the knob where a thin, dense, ruthenium red-positive layer and projecting filaments were present. Freeze-etched material revealed a “particle region” (150–250 nm in thickness) closely associated with the outer cell surface of the suctorian. Fixed specimens were treated with four different lectins and analyzed with electron microscopy in order to obtain information about the carbohydrate composition of the outer surface of D. collini. Concanavalin A bound to the surface of the cell body and tentacle shaft as a dense, particulate layer (80 nm thick) but thinned to 13–16 nm over the surface of the knob. Wheat germ agglutinin-treated cells also displayed a heavy, electron-dense layer (128 nm thick) that surrounded the main cell body and tentacle shaft, but only scattered patches of bound wheat germ agglutinin were observed on the surface of the knob. Discophrya treated with Helix agglutinin or peanut agglutinin appeared similar to control cells. Suctorians were treated with lectins in vivo in an attempt to inhibit capture and ingestion of their prey, Tetrahymena pyriformis, by masking prey receptor sites on the knob. Concanavalin A and, to a lesser degree, wheat germ agglutinin, successfully inhibited attachment of the prey organism. Helix agglutinin and peanut agglutinin had little effect on prey capture.     

Complete Development of Caryospora bigenetica (Apicomplexa: Eimeriidae) In Vitro1

The development of Caryospora bigenetica in vitro is described by light microscopy. Sporozoites from snake-derived oocysts were purified and inoculated onto cultures of primary testicle cells of the cotton rat, cotton rat kidney cells, and human fetal lung cells. Intracellular sporozoites were observed one and two days postinoculation (DPI). Motile, extracellular first-generation merozoites were present 3 DPI, and second-generation merozoites were present 5 DPI. Mature gamonts were observed 9 DPI and developed into unsporulated oocysts by 10 DPI. Oocysts sporulated in vitro, and excystation was observed. Cells that were penetrated by in vitro-produced sporozoites formed caryocysts by 16 DPI. To test infectivity of in vitro-derived stages, merozoites were removed from cultured cells 5 DPI and inoculated intraperitoneally into a mouse; infection resulted. Sporulated oocysts removed from cell cultures 12 DPI produced facial swelling in an orally inoculated cotton rat.     

In Vitro Excystation of Cryptosporidium baileyi from Chickens1

Release of sporozoites from the oocysts of Cryptosporidium baileyi is described from Nomarski interference-contrast microscopy. Just prior to excystation, the four sporozoites became motile and rearranged themselves within the oocyst. The sporozoites were then rapidly expelled through an opening that formed in the oocyst wall, and the residuum was either released or retained within the oocyst. Excysted sporozoites were crescent shaped and measured 5.0–9.0 μm × 1.0–1.6 μm (x?= 6.8 × 1.1 μm). Excystation occurred when sodium taurocholate or a mixture of trypsin and sodium taurocholate was present in the incubation medium. High levels of excystation occurred at 37° or 40°C, but excystation did not occur at 4°C. The ability of biles from two avian and two mammalian hosts to produce excystation of C. baileyi was also studied. After a 2-h incubation at 40°C, the percentages of excystation were 69.5% in goat bile, 45.0% in pig bile, 33.0% in chicken bile, and 34.5% in turkey bile.     

Effect of water availability on leaf water isotopic enrichment in beech seedlings shows limitations of current fractionation models

Current models of leaf water enrichment predict that the differences between isotopic enrichment of water at the site of evaporation (Δ_e) and mean lamina leaf water enrichment (Δ_L) depend on transpiration rates ( E ), modulated by the scaled effective length ( L ) of water isotope movement in the leaf. However, variations in leaf parameters in response to changing environmental conditions might cause changes in the water path and thus L . We measured the diel course of Δ_L for ¹⁸O and ²H in beech seedlings under well-watered and water-limited conditions. We applied evaporative enrichment models of increasing complexity to predict Δ_e and Δ_L, and estimated L from model fits. Water-limited plants showed moderate drought stress, with lower stomatal conductance, E and stem water potential than the control. Despite having double E , the divergence between Δ_e and Δ_L was lower in well-watered than in water-limited plants, and thus, L should have changed to counteract differences in E . Indeed, L was about threefold higher in water-limited plants, regardless of the models used. We conclude that L changes with plant water status far beyond the variations explained by water content and other measured variables, thus limiting the use of current evaporative models under changing environmental conditions.     

Influence of temperature and spawning effort on Haliotis tuberculata mortalities caused by Vibrio harveyi: an example of emerging vibriosis linked to global warming

Since 1998, Haliotis tuberculata mass mortalities have been occurring regularly in wild abalone populations in France during their reproductive period and in conjunction with seawater summer temperature maxima and Vibrio harveyi presence. To confirm the importance of bacterial exposure, temperature and reproductive status on abalone susceptibility, experimental infections via bath exposure were performed using abalone ranging from immature to reproductively mature. Ripe abalone were more susceptible to the bacterium than immature specimens ( P <0.001), and a difference of only 1 °C in temperature had a highly significant impact on the mortalities ( P <0.001). The natural mortalities that were surveyed during summer 2007 confirmed that recent epidemic losses of European abalone appeared in conjunction with host reproductive stress, elevated temperatures and presence of the pathogen V. harveyi . In view of the elevation of the mean summer temperatures observed in Brittany and Normandy over the last 25 years, this temperature-dependent vibriosis represents a new case of emerging disease associated with global warming.