Ecological implications of parasites in natural <Emphasis Type="Italic">Daphnia</Emphasis> populations

In natural host populations, parasitism is considered to be omnipresent and to play an important role in shaping host life history and population dynamics. Here, we study parasitism in natural populations of the zooplankton host Daphnia magna investigating their individual and population level effects during a 2-year field study. Our results revealed a rich and highly prevalent community of parasites, with eight endoparasite species (four microsporidia, one amoeba, two bacteria and one nematode) and six epibionts (belonging to five different taxa: Chlorophyta, Bacillariophyceae, Ciliata, Fungi and Rotifera). Several of the endoparasites were associated with a severe overall fecundity reduction of the hosts, while such effects were not seen for epibionts. In particular, infections by Pasteuria ramosa, White Fat Cell Disease and Flabelliforma magnivora were strongly associated with a reduction in overall D. magna fecundity. Across the sampling period, average population fecundity of D. magna was negatively associated with overall infection intensity and total endoparasite richness. Population density of D. magna was negatively correlated to overall endoparasite prevalence and positively correlated with epibiont richness. Finally, the reduction in host fecundity caused by different parasite species was negatively correlated to both parasite prevalence and the length of the time period during which the parasite persisted in the host population. Consistent with epidemiological models, these results indicate that parasite mediated host damages influence the population dynamics of both hosts and parasites.     

On the applicability of adaptive bioprocess state estimators

This article presents an industrial case study, examining the application of a novel adaptive biomass estimator to an industrial microfungi production process. It is our intention that this contribution should focus upon the implementation issues of the algorithm, in preference to a rigorous theoretical development. The novel algorithm adopted is developed from Adaptive Inferential Estimation studies of Guilandoust and co-workers. The technique utilizes input-output process measurements obtained at different frequencies, thereby providing more frequent estimates of biomass concentration than are otherwise available from off-line laboratory analyses. The algorithm is particularly suited to the biotechnology industry, as it is capable of utilizing irregular assay measurements with varying delays.Although this article demonstrates the encouraging industrial implications of the adaptive algorithm, like all adaptive techniques currently developed, it is restricted by the inability to perform robust on-line system identification. The ultimate selection of a "suboptimal" "fixed parameter" algorithm for on-line implementation, is therefore directly attributable to these inadequacies. Aspects of data acquisition, data pretreatment, and data quality are critical for real process applications, and while some practical approaches are adopted here, many important implementation problems remain unresolved. (c) 1993 John Wiley & Sons, Inc.     

Molecular characterization of Penicillium expansum MUCL mutants

The modern biomolecular analysis of DNA was carried out to determine the identity of Penicillium expansum MUCL V1-V9 Variants with parental strain of Penicillium expansum MUCL 29412 and to compare the results with Penicillium verrucosum, a related species. The extracted DNAs were fragmented by digestion with restriction endonuclease Hind III and the fragments were separated by agarose gel electrophoresis. The DNAs were then denaturated in the gel after partial depurination with dilute acid and were transferred to a nylon membrane. The membrane was incubated with 32P-labeled probe, which was a DNA having a base sequence complementary to the DNA that was to be detected on the filter. The hybridization of the restriction fragments was performed for a highly qualitative comparison of the digested fragments. The analysis of the DNA profile, the most important stage in DNA identity testing, confirms the identity of the DNA for all strains of Penicillium expansum MUCL, except for V5 Variant.     

Dynamic model of hormonal systems coupled by negative feedback

Most hormone concentrations in the body are regulated by negative feedback mechanisms in which the production and release of hormones are regulated according to the concentration of related species. Also, it has been observed that several hormones are released in a variety of pulsatile patterns. In most cases, the mechanism driving these complex patterns is not well understood. Our model of two cells coupled through negative feedback to their external products demonstrates periodic, aperiodic and chaotic oscillations. The coupling between the cells seems to be responsible for these dynamic behaviors. The variety of dynamic behaviors observed in the model demonstrates that a simple physiological feedback loop mimicking the coupling between circulatory hormones and production centers could be the source of complex hormone release patterns observed in vivo.     

Replication fork stalling by bulky DNA damage: localization at active origins and checkpoint modulation

The integrity of the genome is threatened by DNA damage that blocks the progression of replication forks. Little is known about the genomic locations of replication fork stalling, and its determinants and consequences in vivo. Here we show that bulky DNA damaging agents induce localized fork stalling at yeast replication origins, and that localized stalling is dependent on proximal origin activity and is modulated by the intra-S-phase checkpoint. Fork stalling preceded the formation of sister chromatid junctions required for bypassing DNA damage. Despite DNA adduct formation, localized fork stalling was abrogated at an origin inactivated by a point mutation and prominent stalling was not detected at naturally-inactive origins in the replicon. The intra-S-phase checkpoint contributed to the high-level of fork stalling at early origins, while checkpoint inactivation led to initiation, localized stalling and chromatid joining at a late origin. Our results indicate that replication forks initially encountering a bulky DNA adduct exhibit a dual nature of stalling: a checkpoint-independent arrest that triggers sister chromatid junction formation, as well as a checkpoint-enhanced arrest at early origins that accompanies the repression of late origin firing. We propose that the initial checkpoint-enhanced arrest reflects events that facilitate fork resolution at subsequent lesions.