Does elevated testosterone result in increased exposure and transmission of parasites?

Male-biased infection is a common phenomenon in vertebrate-parasite systems and male-biased transmission has been experimentally demonstrated. One mechanism that is hypothesized to create male-biased transmission is the immuno-suppressive effect of testosterone because it increases susceptibility to infection. Testosterone also influences host behaviour and, consequently, may increase exposure to parasites. To test how testosterone could increase exposure and transmission, we undertook a longitudinal mark-recapture study where we experimentally elevated testosterone levels in wild male rodents. Individuals in control populations reduced the average number of contacts over the treatment period, while populations with experimentally elevated testosterone levels maintained the number of contacts between hosts. As a result, the transmission potential was higher in testosterone treated populations compared to controls. Our results indicated that males with high-testosterone levels alter the population-level contacts, producing different social networks and increasing transmission potential compared to those where testosterone is at background levels.     

Applications of genome‐scale metabolic reconstructions

The availability and utility of genome‐scale metabolic reconstructions have exploded since the first genome‐scale reconstruction was published a decade ago. Reconstructions have now been built for a wide variety of organisms, and have been used toward five major ends: (1) contextualization of high‐throughput data, (2) guidance of metabolic engineering, (3) directing hypothesis‐driven discovery, (4) interrogation of multi‐species relationships, and (5) network property discovery. In this review, we examine the many uses and future directions of genome‐scale metabolic reconstructions, and we highlight trends and opportunities in the field that will make the greatest impact on many fields of biology.     

Is the combination of topsoil replacement and inoculation with plant material an effective tool for the restoration of threatened sandy grassland?

Question: Is it possible to restore dry calcareous inland sand ecosystems with their characteristic plant community structure within a 4‐yr period by means of combined abiotic–biotic techniques (topsoil replacement, inoculation with raked/mown plant material from target areas)? Location: Upper Rhine valley, Germany. Methods: Two 4‐year experiments were carried out on former arable land, each in the proximity of a reference area bearing a similar complex of threatened sandy grasslands (experiment 1: fine‐scale; experiment 2: landscape scale). In both experiments we used nutrient‐poor deep‐sand substrate (abiotic approach), raked/mown inoculation material from target areas and grazing as management tool (biotic and management approach). The vegetation of the restoration and donor areas was sampled once a year and analysed by non‐metric multidimensional scaling (NMDS) ordination and target‐species ratios. Mixed linear models were calculated to determine effects of grazing (experiment 1) and year (both experiments). Results: NMDS revealed a continuous development of the restored sites towards the corresponding donor sites. Similarly, target‐species ratios of the restored sites tended towards the ratios of the donor sites. To date, grazing effects have mainly been structural: reduction of a carpet‐forming pleurocarpous moss species and of litter. In addition, cover of target species in relation to total plant cover was significantly enhanced by grazing in the last two study years. Conclusions: The combination of nutrient‐poor substrate, inoculation with raked/mown plant material and grazing proved to be a very effective restoration method for dry base‐rich sand ecosystems. After 4 yr the restored plant communities serve as well‐developed parts of a habitat network.     

Developing a Benthic Index of Biological Integrity and Some Relationships to Environmental Factors in the Subtropical Xiangxi River,China

The aim of this study is to develop a benthic index of biotic integrity (B‐IBI) to help understand how the increasing anthropogenic pressure may impact the subtropical Xiangxi River in China. Benthic macroinvertebrate and environmental surveys were conducted at 77 sites in early summer 2004. Each collection site was categorized as reference or impaired based on physical, chemical, biological, and land‐use information. Six non‐redundant metrics from 35 metrics were used to differentiate between reference and impaired sites. We selected six metrics for the final IBI. The scoring criteria of each metric were normalized based on the quadrisection and 0–10 scaling systems. Both scaling methods were used to assess the aquatic health of each site in the Xiangxi River watershed. The results showed that most sites were in fairly poor condition. Furthermore, we identified the relationship between B‐IBI metrics, water‐quality, and land‐use variables with a principal component analysis. A composite of nutrients and land‐use intensity explained most variances. These results suggest that the B‐IBI may be a suitable method for assessing river conditions within the subtropical Xiangxi River in central China (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Differentiation of probiotic and environmental Saccharomyces cerevisiae strains in animal feed

Aims: To establish an identification system for probiotic Saccharomyces cerevisiae strains based on artificial neural network (ANN)–assisted Fourier‐transform infrared (FTIR) spectroscopy to improve quality control of animal feed. Methods and Results: The ANN‐based system for differentiating environmental from probiotic S. cerevisiae strains comprises five authorized feed additive strains plus environmental strains isolated from different habitats. A total of 108 isolates were used as reference strains to create the ANN. DHPLC analysis and δ‐PCR were used as reference methods to type probiotic yeast isolates. The performance of the FTIR‐ANN was tested in an internal validation using unknown spectra of each reference strain. This validation step yielded a classification rate of 99·1 %. For an external validation, a test data set comprising 965 spectra of 63 probiotic and environmental S. cerevisiae isolates unknown to the ANN was used, resulting in a classification rate of 98·2 %. Conclusions: Our results demonstrate that probiotic S. cerevisiae strains in feed can be differentiated successfully from environmental isolates using both genotypic approaches and ANN‐based FTIR spectroscopy. Significance and Impact of the Study: FTIR‐based artificial neural network analysis provides a rapid and inexpensive technique for yeast identification both at the species and at the strain level in routine diagnostic laboratories, using a single sample preparation.     

Characterization of a new xyloglucan endotransglucosylase/hydrolase (XTH) from ripening tomato fruit and implications for the diverse modes of enzymic action

Xyloglucan endotransglucosylase/hydrolases (XTHs) are cell wall-modifying enzymes that align within three or four distinct phylogenetic subgroups. One explanation for this grouping is association with different enzymic modes of action, as XTHs can have xyloglucan endotransglucosylase (XET) or endohydrolase (XEH) activities. While Group 1 and 2 XTHs predominantly exhibit XET activity, to date the activity of only one member of Group 3 has been reported: nasturtium TmXH1, which has a highly specialized function and hydrolyses seed-storage xyloglucan rather than modifying cell wall structure. Tomato fruit ripening was selected as a model to test the hypothesis that preferential XEH activity might be a defining characteristic of Group 3 XTHs, which would be expressed during processes where net xyloglucan depolymerization occurs. Database searches identified 25 tomato XTHs, and one gene (SlXTH5) was of particular interest as it aligned within Group 3 and was expressed abundantly during ripening. Recombinant SlXTH5 protein acted primarily as a transglucosylase in vitro and depolymerized xyloglucan more rapidly in the presence than in the absence of xyloglucan oligosaccharides (XGOs), indicative of XET activity. Thus, there is no correlation between the XTH phylogenetic grouping and the preferential enzymic activities (XET or XEH) of the proteins in those groups. Similar analyses of SlXTH2, a Group 2 tomato XTH, and nasturtium seed TmXTH1 revealed a spectrum of modes of action, suggesting that all XTHs have the capacity to function in both modes. The biomechanical properties of plant walls were unaffected by incubation with SlXTH5, with or without XGOs, suggesting that XTHs do not represent primary cell wall-loosening agents. The possible roles of SlXTH5 in vivo are discussed.