A Screenable <em>In Vivo</em> Assay for Mitochondrial Modulators Using Transgenic Bioluminescent <em>Caenorhabditis elegans</em>

The multicellular model organism Caenorhabditis elegans is a small nematode of approximately 1 mm in size in adulthood that is genetically and ...

University of Aberdeen

The community structure of rhizosphere soil Archaea from three grassland types, associated with different management practices, was examined at a site in the Borders region of Scotland, by analysis of 16S rRNA gene fragments amplified from 16S rDNA and from rRNA. Denaturing gradient gel electrophoresis (DGGE) and sequence analysis of amplified products indicated high relative abundance within the archaeal community of two distinct lineages of non-thermophilic (group 1) Crenarchaeota. Grassland management practices influenced archaeal community structure, as characterized by both 16S rRNA- and 16S rDNA-derived DGGE profiles. One band dominated DGGE profiles in all three grassland types examined, and reproducible differences in the presence and intensity of bands were observed between profiles from managed and natural grassland sites. Analysis of 16S rRNA-derived amplicons from managed and natural grasslands at sites in the north of England and the north of Wales also indicated high relative abundance of non-thermophilic crenarchaeotes within the archaeal community. The band dominating the Scottish grassland site also dominated DGGE profiles from the English and Welsh sites, and similar differences were seen between profiles derived from soils subjected to different management regimes. The study indicates that grassland archaeal communities are dominated by Crenarchaeota, with closely related members of this lineage ubiquitous in distribution in UK upland pasture, and indicate that management practices influence the nature of the crenarchaeotal community.

The impact of grassland management on archaeal community structure in upland pasture rhizosphere soil.

The complex structure of soil and the heterogeneity of resources available to microorganisms have implications for sampling regimens when the structure and diversity of microbial communities are analyzed. To assess the heterogeneity in community structure, archaeal communities, which typically contain sequences belonging to the nonthermophilic Crenarchaeota, were examined at two contrasting spatial scales by using PCR-denaturing gradient gel electrophoresis (DGGE) analysis followed by unweighted pair group method with arithmetic mean analysis of 16S rRNA- and ribosomal DNA-derived profiles. A macroscale analysis was carried out with soil cores taken at 2-m intervals along triplicate 8-m transects from both managed (improved) and natural (unimproved) grassland rhizosphere soils. A microscale analysis was carried out with a single soil core by assessing the effects of both sample size (10, 1, and 0.1 g) and distance between samples. The much reduced complexity of archaeal profiles compared to the complexity typical of the bacterial community facilitated visual comparison of profiles based on band presence and revealed different levels of heterogeneity between sets of samples. At the macroscale level, heterogeneity over the transect could not be related to grassland type. Substantial heterogeneity was observed across both improved and unimproved transects, except for one improved transect that exhibited substantial homogeneity, so that profiles for a single core were largely representative of the entire transect. At the smaller scale, the heterogeneity of the archaeal community structure varied with sample size within a single 8- by 8-cm core. The archaeal DGGE profiles for replicate 10-g soil samples were similar, while those for 1-g samples and 0.1-g samples showed greater heterogeneity. In addition, there was no relationship between the archaeal profiles and the distance between 1- or 0.1-g samples, although relationships between community structure and distance of separation may occur at a smaller scale. Our findings demonstrate the care required when workers attempt to obtain a representative picture of microbial community structure in the soil environment.

Spatial analysis of archaeal community structure in grassland soil.

Grassland management regimens influence the structure of archaeal communities in upland pasture soils, which appear to be dominated by as yet uncultivated non-thermophilic Crenarchaeota. In an attempt to determine which grassland management factors select for particular crenarchaeal community structures, soil microcosm experiments were performed examining the effect of increased pH, application of inorganic fertilizer (ammonium nitrate) and sheep urine deposition on both archaeal and bacterial communities in unmanaged grassland soil. As grassland management typically increases pH, a further experiment examined the effect of a reduction in pH, to that typical of unimproved grassland soils, on archaeal and bacterial communities. The RT-PCR amplification of 16S rRNA followed by denaturing gradient gel electrophoresis analysis demonstrated a distinct and reproducible effect on bacterial communities after incubation for 28 or 30 days. In contrast, none of the treatments had a significant effect on the structure of the crenarchaeal community, indicating that these factors are not major drivers of crenarchaeal community structures in grassland soils.

Differential response of archaeal and bacterial communities to nitrogen inputs and pH changes in upland pasture rhizosphere soil.

In the C. albicans retrotransposon Tca2, the gag and pol ORFs are separated by a UGA stop codon, 3' of which is a potential RNA pseudoknot. It is unclear how the Tca2 gag UGA codon is bypassed to allow pol expression. However, in other retroelements, translational readthrough of the gag stop codon can be directed by its flanking sequence, including a 3' pseudoknot.

Control of gag-pol gene expression in the Candida albicans retrotransposon Tca2.

The ATP levels of an organism are an important physiological parameter that is affected by genetic make up, ageing, stress and disease.

Bridging the phenotypic gap: real-time assessment of mitochondrial function and metabolism of the nematode Caenorhabditis elegans.

Sublethal metabolic effects are informative toxicological end points. We used a rapid quantitative metabolic end point, bioluminescence of firefly luciferase expressing Caenorhabditis elegans, to assess effects of sublethal chronic exposure (19 h) to the oxidative stress agent and environmental pollutant cadmium (provided as chloride salt). Bioluminescence declined in a concentration-dependent manner in the concentration range tested (0-30 microM Cd), with comparable sensitivity to reproduction and developmental assay end points (after 67 and 72 h, respectively). Cd concentrations that resulted in 20% reduction in bioluminescence (EC(20)) were 11.8-13.0 microM, whereas the reproduction EC(20) (67 h exposure) was 10.2 microM. At low concentrations of Cd (< or = 15 microM), the decline in bioluminescence reflected a drop in ATP levels. At Cd concentrations of 15-30 microM, decreased bioluminescence was attributable both to effects of Cd on ATP levels and decreased production of luciferase proteins, concomitant with a decline in protein levels. We show that whole-animal bioluminescence is a valid toxicological end point and a rapid and sensitive predictor of effects of Cd exposure on development and reproduction. This provides a platform for high-throughput sublethal screening and will potentially contribute to reduction of testing in higher animals.

Rapid sublethal toxicity assessment using bioluminescent Caenorhabditis elegans, a novel whole-animal metabolic biosensor.

Abstract Quantitative models of bacterial conjugation are useful tools in environmental risk assessment and in studies of the ecology and evolution of bacterial communities. We constructed a mathematical model for gene transfer between bacteria growing on a solid surface. The model considers that donor and recipient cells will form separate colonies, which grow exponentially until nutrient exhaustion. Conjugation occurs when donor and recipient colonies meet, all recipient cells becoming transconjugants instantly, after which they act as donors. The model was tested theoretically by computer simulations that followed the histories of individual bacterial colonies and was validated for initial surface coverage of 60% or less, where confluent growth does not occur. Model predictions of final number of donors, recipients and transconjugants were tested experimentally using a filter mating system with two isogenic strains of Pseudomonas fluorescens MON787 acting as donor and recipient of plasmid RP4. Experimental trends resulting from varying donor and recipient inoculum numbers and donor:recipient ratios were well described by the model, although it often overestimated conjugation by 0.5-2 orders of magnitude. Predictions were greatly improved, generally to within half a log unit of experimental values, by consideration of the time for conjugative transfer. The model demonstrates the relationship between spatial separation of cells and nutrient availability on numbers of transconjugants. By providing a mechanistic approach to the study conjugation on surfaces, the model may contribute to the study of gene transfer in natural environments.

A model for bacterial conjugal gene transfer on solid surfaces.

A transgenic strain of the model nematode Caenorhabditis elegans in which bioluminescence reports on relative, whole-organism ATP levels was used to test an environmentally-relevant mixture of pollutants extracted from processed sewage sludge. Changes in bioluminescence, following exposure to sewage sludge extract, were used to assess relative ATP levels and overall metabolic health. Reproductive function and longevity were also monitored. A short (up to 8 h) sublethal exposure of L4 larval stage worms to sewage sludge extract had a concentration-dependent, detrimental effect on energy status, with bioluminescence decreasing to 50-60% of the solvent control (1% DMSO). Following longer exposure (22-24 h), the energy status of the nematodes showed recovery as assessed by bioluminescence. Continuous exposure to sewage sludge extract from the L4 stage resulted in a shorter median lifespan relative to that of solvent or medium control animals, but only in the presence of 400-600 µM 5-fluoro-2'-deoxyuridine (FUdR), which was incorporated to inhibit reproduction. This indicated that FUdR increased lifespan, and that the effect was counteracted by SSE. Exposure to sewage sludge extract from the L1 stage led to slower growth and a delayed onset of egg laying. When L1 exposed nematodes reached the reproductive stage, no effect on egg laying rate or egg number in the uterus was observed. DMSO itself (1%) had a significant inhibitory effect on growth and development of C. elegans exposed from the L1 stage and on reproduction when exposed from the L4 stage. Results demonstrate subtle adverse effects on C. elegans of a complex mixture of environmental pollutants that are present, individually, in very low concentrations and indicate that our biosensor of energy status is a novel, sensitive, rapid, quantitative, whole-organism test system which is suitable for high throughput risk assessment of complex pollutant mixtures.

L. Anne Glover

Institute of Medical Sciences

University of Aberdeen

A Screenable In Vivo Assay for Mitochondrial Modulators Using Transgenic Bioluminescent Caenorhabditis elegans

L. Anne Glover

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Institute of Medical Sciences

University of Aberdeen

A Screenable In Vivo Assay for Mitochondrial Modulators Using Transgenic Bioluminescent Caenorhabditis elegans

Institute of Medical Sciences