Ecological implications on the aggregation of <Emphasis Type="Italic">Amblyomma fuscum</Emphasis> (Acari: Ixodidae) on <Emphasis Type="Italic">Thrichomys laurentius</Emphasis> (Rodentia: Echimyidae), in northeastern Brazil

We investigated the Amblyomma fuscum load on a pullulating wild rodent population and the environmental and biological factors influencing the tick load on the hosts. One hundred and three individuals of Thrichomys laurentius were caught in an Atlantic forest fragment in northeastern Brazil, as part of a longitudinal survey on ticks infesting non-volant small mammals. Ticks (n = 342) were found on 45 individuals and the overall mean intensity of infestation was 7.6 ticks per infested rodent. Ticks were highly aggregated in the host population and the negative binomial distribution model provides a statistically satisfactory fit. The aggregated distribution was influenced by sex and age of the host. The microhabitat preference by T. laurentius probably increases contact opportunities between hosts and aggregated infesting stages of the ticks and represents important clues about the habitat suitability for A. fuscum.     

A metabolic model for acetate uptake under anaerobic conditions by glycogen accumulating organisms: Stoichiometry, kinetics, and the effect of pH

A metabolic model for the stoichiometry of acetate uptake under anaerobic conditions by an enriched culture of glycogen accumulating organisms (GAOs) was developed and tested by experimental studies. Glycogen served as the source of both reducing power and energy to drive the process of acetate uptake. The amount of glycogen consumed and poly-beta-hydroxyvalerate (PHV) accumulated in the cells increased with increasing pH, indicating that the energy requirements for acetate uptake increased with pH. The composition of the accumulated poly-beta-hydroxyalkanoates (PHAs) was adequately predicted using the assumption that acetyl-CoA and propionyl-CoA condense randomly to produce PHA. In addition, the rate of acetate uptake was strongly affected by the pH. The rate decreased with increasing pH and this dependence could be described with a saturation type of expression. A comparison of the rate of acetate uptake at low pH with the rates observed in enriched cultures of phosphorus accumulating organisms (PAOs) indicated that GAOs are able to compete effectively with PAOs in nutrient removal systems under certain conditions.     

Requirements of peptidoglycan structure that allow detection by the Drosophila Toll pathway

The Drosophila immune system is able to discriminate between classes of bacteria. Detection of Gram-positive bacteria involves a complex of two pattern recognition receptors: peptidoglycan recognition protein SA (PGRP-SA) and Gram-negative binding protein 1 (GNBP1). These activate the Toll signalling pathway. To define the cell wall components sensed by the host, we used highly purified peptidoglycan fragments of two principal Gram-positive bacterial pathogens Staphylococcus aureus and Streptococcus pneumoniae. We report that in both peptidoglycans, the minimal structure needed to activate the Toll pathway is a muropeptide dimer and that the free reducing end of the N-acetyl muramic acid residues of the muropeptides is essential for activity. Monomeric muropeptides were inactive and inhibitory in combination with dimers. Finally, peptidoglycan was degraded by the haemolymph of wild-type but not GNBP1 mutant flies. We suggest a model whereby GNBP1 is involved in the hydrolysis of Gram-positive peptidoglycan producing new glycan reducing ends, which are subsequently detected by PGRP-SA.     

Detection of DNA strand breakage in a marine amphipod by agarose gel electrophoresis: exposure to X-rays and copper.

This article describes the leading steps to develop an assay of DNA damage for the marine amphipod Gammarus locusta, using agarose gel electrophoresis (AGE). To test the sensitivity and feasibility of the AGE technique, X-ray assays were performed with naked DNA and with live amphipods. These positive controls demonstrated the effectiveness of the AGE technique to not only discriminate distinct levels of DNA strand breakage in a dose-dependent manner, but also to identify and quantify the type of strand breakage induced. It was also shown that it is possible to detect DNA damage using whole-body DNA extracts from amphipods. To explore the potential of this technique for use in ecotoxicological studies with amphipods, a 96-h waterborne-copper toxicity test was performed. Copper-induced DNA strand breakage was first observed after 24 h of exposure, and was recorded again at 96 h, at a copper concentration of 20 microg l(-1). The absence of strand breakage after 48 h of exposure is discussed in the light of the underlying mechanisms of copper toxicity and DNA repair. These studies demonstrated the feasibility of including DNA damage as a biomarker in ecotoxicological studies with amphipods. Information gained from the use of this biomarker would help with the interpretation of chronic toxicity tests and would contribute to our understanding of the impact of genotoxic insult in marine invertebrates, particularly crustaceans.