Influences on the antimicrobial activity of surface-adsorbed nisin

The efficacy of the antimicrobial peptide nisin was examined after adsorption to silica surfaces. Three protocols were used to evaluate nisin's activity against adhered cells ofListeria monocytogenes: bioassay usingPediococcus pentosaceous FBB 61-2 as the sensitive indicator strain; visualization and enumeration of cells by microscopic image analysis; and viability of adhered cells as determined by lodonitrotetrazolium violet uptake and crystallization. The activity of adsorbed nisin was highly dependent upon conditions of adsorption. The highest antimicrobial activity of adsorbed nisin occurred with high concentrations of nisin (1.0 mg ml^–1) and brief contact times (1 h) on surfaces of low hydrophobicity. Sequential adsorption of a second protein (-lactoglobulin or bovine serum albumin) onto surfaces consistently resulted in decreased nisin activity. These data provide direction for the development of applications to limit microbial attachment on food contact surfaces through the use of adsorbed antimicrobial peptides.     

Pine needle growth and fine structure after prolonged acid rain treatment in the subarctic

The growth and morphology of Scots pine needles were studied in a long-term acid rain experiment in the far north of Finnish Lapland. Pine trees 5 m tall of age 50–70 years were exposed, by spraying the foliage and soil from a height of 2 m, to either clean water (IC) or acidified water over the period 1985–1992, the acidification site being divided into sub-areas in which the precipitation contained two levels of either sulphuric (Sm, Sh) or nitric (Nm, Nh) acid, or both (SNm, SNh). The treatments with medium and high sulphate-S over eight consecutive years yielded a total sulphur deposition of 3·4 and 17·1 gm⁻², respectively, and those with medium and high nitrate-N a total nitrogen deposition of 1·1 and 5·9 g m⁻². Needles were collected for light and electron microscopy, growth measurements and morphometry. Growth in branch height had decreased by about 40% after 6 years of SNm or SNh treatment, and needle growth by 15% in the SNh trees as compared with the irrigated control trees (IC), although decreases were statistically significant only with respect to the non-irrigated control trees (DC). Growth of branches and needles was slightly better in the Nh treatment than in the IC group. The areas of the whole needle, the mesophyll and the phloem decreased in response to SNh treatment as compared with IC or DC, and a statistically significant decrease of about 30–40% was seen in the area of the xylem in comparison with DC. Cellular damage was observed following the acid treatments, especially with a high acid load. The damage was manifested in collapse of the cellular compartments, increases in lipid accumulations and swelling or disorganization of the protoplast. Increased vacuolization of the cytoplasm, plasmalemma irregularities and chilling-type damage to the mitochondria were also observed.     

Macroecology of Aquatic Insects: A Quantitative Analysis of Taxonomic Richness and Composition in the Andes Mountains of Northern Ecuador

To determine the spatial dynamics of Neotropical lotic insect species, specimens were collected from 41 streams on the eastern and western flanks of the Andes Mountains in Ecuador. We examined the manner in which taxonomic richness and composition differed with elevation, latitude, and versant. Statistical analyses were limited to 5 families (Ephemeroptera: Baetidae, Leptohyphidae, Oligoneuriidae; Heteroptera: Naucoridae; Coleoptera: Elmidae), comprising 32 genera and 85 species, for which identifications or morphospecies assignments were reliable. Assessment of taxonomic diversity was based on the richness of genera and species at each site. In addition, each site was characterized by species richness within each of 4 families with more than 10 species. The effects of versant and transect on composition and structure were family‐specific. Mean site differences between versants in elmid richness at generic and specific levels depended on transect. Only baetid richness was affected by versant and transect in a consistent manner. Variation among sites in composition based on all genera and species was captured using multidimensional scaling (MDS). Subsequent MANOVAs based on scores from MDS axes revealed that differences between versants were much stronger in the southern transect, although transects differed from each other at specific and generic levels. A Jaccard's similarity matrix was computed for each family to reflect the spatial organization of taxonomic composition. Mesogeographic patterns of species composition for each of the four families were correlated (Mantel analysis) at both the regional level and at the level of the entire study area. At the regional level, the only pair of families to exhibit correlated patterns of species composition was elmids and naucorids in the southwestern region. The pattern of species composition for each family was correlated with the patterns for one or more other families at the level of the entire study area. Thus, spatial dynamics of species composition was similar for the families examined, suggesting that the Andes exert a consistent influence on species distributions within families, regardless of ordinal affiliation. At a local scale, however, the way in which taxonomic composition changed with latitude and versant was family‐specific. Mayflies, the most vagile of the taxa studied, had the highest percentage of species overlap between versants. Of three genera of Naucoridae collected, species of Ambrysus, of probable Mexican origin, were found only on the eastern versant, corroborating other evidence that the genus is recent in South America. Moreover, dispersion by Ambrysus across the Andes Mountains may not have occurred, as it has for Cryphocricos and Limnocoris, which are of probable South American origin.     

Cost modelling of Pseudomonas fluorescens and Pseudomonas chlororaphis as biocontrol for competitive exclusion of Salmonella enterica on tomatoes

Published research on process-based models for biocontrol of foodborne pathogens on produce is limited. The aim of this research was to develop cost model estimates for competitive exclusion (CE) process using Pseudomonas fluorescens and Pseudomonas chlororaphis (non-plant pathogenic and non-human pathogen) as biocontrol against Salmonella enterica on tomatoes. Cost estimates were based on material inputs, equipment, facilities, and projected processing conditions of post-harvest packaging of tomatoes. The microbiological data for inactivation of S. enterica was based on published papers. The small-scale processing facility was assumed to have a processing capacity of 2000 kg of tomatoes/hour for 16 h per day, operational 6 days a week, and for 3-months /year. The large-scale facility was assumed to have a processing capacity of 100,000 kg of tomatoes/hour. Estimated initial capital investment costs for small and large-scale models (production facility) were US$391,000 and US$2.1 million. Application of CE for biocontrol of S. enterica on tomatoes was estimated at US$0.0058–0.073/kg of tomatoes during commercial processing operations. This exceeds chlorine wash technology estimated at US$0.00046/kg and is competitive with gaseous chlorine dioxide at US$0.02–0.21/kg. For high-value produce, CE may complement existing technologies increase food safety, reduce storage loses, and extend shelf life of produce.     

A molecular phylogeny of the lizard genus Phymaturus (Squamata,Liolaemini): Implications for species diversity and historical biogeography of southern South America

The lizard genus Phymaturus is widely distributed in Argentina and along the eastern edge of Chile between 25° and 45° south. We sampled 27 of the 38 currently recognized species plus 22 candidate species using two mitochondrial genes (cytb and 12S), four protein coding nuclear genes and seven anonymous nuclear loci, and present the first comprehensive molecular phylogenetic hypothesis for the clade. We recovered two large clades (the palluma or northern group and patagonicus or southern group) previously recognized on the basis of morphological and mitochondrial sequence evidence, and compared results obtained from concatenated-gene analyses with results of a coalescent-based species-tree approach (BEST). With both methods we identified four main clades within the palluma group (mallimaccii, roigorum, verdugo, and vociferator) and five main clades within the patagonicus group (calcogaster, indistinctus, payuniae, somuncurensis, and spurcus). We found several instances of non-monophyly with cytb and cases of incongruence between mitochondrial vs nuclear data for which we discuss alternative hypotheses. Although with lower support values, combined BEST results are more congruent with concatenated nuclear data than with combined concatenated analyses, suggesting that BEST is less influenced by demographic processes than combined concatenated analyses. We discuss the taxonomic, biogeographic and conservation implications of these results and how the future integration of phylogeographic and morphological approaches will allow the further testing of demographic and biogeographic hypotheses.     

A comparison of nuclear and mitochondrial cline shapes in a hybrid zone in the Sceloporus grammicus complex (Squamata; Phrynosomatidae)

The F5 and FM2 chromosome races of the Sceloporus grammicus complex form a hybrid zone in the Mexican state of Hidalgo. Previous studies of this zone have assessed genetic structure by averaging estimates of shape and width across three diagnostic chromosome markers. This approach is likely to mask subtle differences in cline shape among loci (e.g. selected vs. neutral), and obscure any displacement of cline centres (if present). Here we use maximum likelihood methods to construct the best fitting individual clines for three chromosomal markers, and also add two new markers; the mitochondrial DNA (mtDNA) locus, and the nuclear ribosomal DNA (rDNA) repeat. For each locus, hybrid zone models were fitted by cline shape and width, and the position and number of segments describing the centre of the zone. Pairwise comparisons between all clines revealed concordance between chromosomes 2 and 6, but significant discordance in cline structure among all other paired combinations. The concordance of chromosomes 2 and 6 suggests that these clines are maintained by genome-wide forces. The discordance of the chromosome 1 cline suggests an influence of asymmetric introgression, while the mtDNA cline is probably influenced by selection and drift. The rDNA locus reveals a pattern best explained by either extreme asymmetric introgression or gene conversion. The structure of zone indicates that genome-wide processes and locus specific selective forces as well as drift, are operating to different degrees on different loci. The locus-by-locus approach used here permits a finer discrimination among possible mechanisms responsible for the maintenance of the individual clines.     

What Drives Chytrid Infections in Newt Populations? Associations with Substrate,Temperature, and Shade

The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) is considered responsible for the population declines and extinctions of hundreds of amphibian species worldwide. The panzootic was likely triggered by human-assisted spread, but once the pathogen becomes established in a given region, its distribution is probably determined by local drivers. To assess the relative importance of potential drivers of infection in red-spotted newts (Notophthalmus viridescens), we measured Bd levels in 16 populations throughout central Pennsylvania. Infected individuals were detected in all but four populations, indicating that Bd is widespread in this region. We quantified local factors hypothesized to influence Bd, and found that infection levels were best predicted by the proportion of the pond substrate consisting of leaf litter or vegetation, along with a significant effect of water temperature. Bd infection in amphibians is temperature-dependent, and one possible explanation of the apparent substrate effect is that tree cover and vegetation provide shade, reducing the availability of shallow, warm-water patches in which newts might reduce or clear Bd infections. Alternatively, leaf litter and emergent vegetation might increase Bd infection more directly, perhaps by providing substrates for environmental growth of the fungus. We also observed a curvilinear relationship between Bd load and snout-vent length (a proxy for age), hinting that newts might develop acquired resistance to Bd infection. Though correlational, these results add to a growing body of evidence suggesting that environmental temperature is an important driver of Bd infection dynamics.     

Least-desired index for assessing the effectiveness of grass riparian filter strips in improving water quality in an agricultural region

Unprotected streams within the agricultural Midwest region of the United States are subject to sedimentation, nutrification, and agricultural chemicals. Grass riparian filter strips (GRFSs) have been implemented as a best management practice to minimize sedimentation and associated materials that are harmful to aquatic ecosystems; however, few studies have examined the benthic community response to GRFS installation. This study introduces a least-desired index (LDI) multimetric approach of evaluating benthic communities in response to GRFS installation. LDI was determined in a reciprocal fashion to that of a benthic macroinvertebrate index of biotic integrity (B-IBI). When reference conditions are not available for the use of B-IBI, anti-reference sites, representing least-desired conditions, can be used in constructing an LDI. A B-IBI and LDI were constructed in the Claypan Till Plains Subsection of Missouri and comparatively used to evaluate two test sites where tall fescue GRFS were installed. Five metrics were used to develop the B-IBI and six for the LDI. The LDI tended to be more conservative at evaluation in comparison to the B-IBI. Paired t-tests showed that LDI and B-IBI were significantly different at scoring test sites. The LDI assessed both test sites as showing no response to GRFS installation, whereas the B-IBI suggested moderate improvement. The LDI was considered to be a better index for evaluation because the streams used to develop the B-IBI were not suitable reference sites. An argument for the use of chironomid based metrics in low gradient agricultural streams is presented.     

Molecular evidence for a species complex in the patagonian lizard Liolaemus bibronii and phylogeography of the closely related Liolaemus gracilis (Squamata: Liolaemini)

The lizard genus Liolaemus is endemic to temperate South America and includes 190 species. Liolaemus bibronii has a large geographic distribution and inhabits a great diversity of habitats, including the Monte, Steppe, and high Andean grassland environments. Liolaemus gracilis has a similar body size and shape to L. bibronii; the two are parapatrically distributed, and L. gracilis is also widely distributed. Here we use the mtDNA cytb sequence data of these two species to investigate lizard phylogeographic patterns in southern South America. L. bibronii is paraphyletic with respect to L. gracilis, Liolaemus ramirezae, Liolaemus robertmertensi and Liolaemus saxatilis; it is composed of many genetically different allopatric haploclades, some of which are reciprocally monophyletic. We also found evidence for introgression between L. bibronii and L. gracilis in the same area that introgression was hypothesized in the Liolaemus darwinii complex. We discuss the distribution of the major haploclades with inferences of their population histories, the concordance of these clades' distributions and histories with other lizard complexes studied with the same markers and methods, and taxonomic implications of these results.