Diversity of the active methanotrophic community in acidic peatlands as assessed by mRNA and SIP-PLFA analyses

The active methanotroph community was investigated for the first time in heather (Calluna)-covered moorlands and Sphagnum/Eriophorum-covered UK peatlands. Direct extraction of mRNA from these soils facilitated detection of expression of methane monooxygenase genes, which revealed that particulate methane monooxygenase and not soluble methane monooxygenase was probably responsible for CH(4) oxidation in situ, because only pmoA transcripts (encoding a subunit of particulate methane monooxygenase) were readily detectable. Differences in methanotroph community structures were observed between the Calluna-covered moorland and Sphagnum/Eriophorum-covered gully habitats. As with many other Sphagnum-covered peatlands, the Sphagnum/Eriophorum-covered gullies were dominated by Methylocystis. Methylocella and Methylocapsa-related species were also present. Methylobacter-related species were found as demonstrated by the use of a pmoA-based diagnostic microarray. In Calluna-covered moorlands, in addition to Methylocella and Methylocystis, a unique group of peat-associated type I methanotrophs (Gammaproteobacteria) and a group of uncultivated type II methanotrophs (Alphaproteobacteria) were also found. The pmoA sequences of the latter were only distantly related to Methylocapsa and also to the RA-14 group of methanotrophs, which are believed to be involved in oxidation of atmospheric concentrations of CH(4). Soil samples were also labelled with (13)CH(4), and subsequent analysis of the (13)C-labelled phospholipid fatty acids (PLFAs) showed that 16:1 omega 7, 18:1 omega 7 and 18:1 omega 9 were the major labelled PLFAs. The presence of (13)C-labelled 18:1 omega 9, which was not a major PLFA of any extant methanotrophs, indicated the presence of novel methanotrophs in this peatland.

Impact of water table depth on forest soil methane turnover in laboratory soil cores deduced from natural abundance and tracer 13C stable isotope experiments

We investigated turnover of methane (CH4) in soils from a poorly drained UK forest. In situ, this forest exhibited a negligible soil-atmosphere CH4 flux, whereas adjacent grassland plots were sources of CH4. We hypothesised that the forest plots exhibited reduced anaerobic CH4 production through water-table draw down. Consequently, we exposed soil cores from under oak to high and low water-table conditions in the laboratory. Methane fluxes increased significantly in the high water-table (1925+/-1702 mug CH4 m(-2) h(-1)) compared to the low one (-3.5+/-6.8 microg CH4 m(-2) h(-1)). Natural abundance delta13C values of CH4 showed a strong depletion in high water-table cores (-56.7+/-2.9 per thousand) compared to methane in ambient air (-46.0 per thousand) indicative of methanogenic processes. The delta13C values of CH4 from low water-table cores (delta13C-46.8+/-0.2 per thousand) was similar to ambient air and suggested little alteration of headspace CH4 by the soil microbial community. In order to assess the CH4 oxidizing activity of the two treatments conclusively, a 13CH4 spike was added to the cores and 13CO2 production was measured as the by-product of CH4 oxidation. 13CH4 oxidation rates were 57.5 (+/-12.7) and 0.5 (+/-0.1) microg CH4 m(-2) h(-1) for high and low water-tables, respectively. These data show that the lower water-table hydrology treatment impacted methanogenic processes without stimulating methanotrophy.

Fatty acid compositions of Collembola: unusually high proportions of C20 polyunsaturated fatty acids in a terrestrial invertebrate

To examine the C(20) polyunsaturated fatty acid (PUFA) compositions of Collembola, we raised five species of Collembola on yeast diets, and then quantified body mass, neutral lipid fatty acid (NLFA) and phospholipid fatty acid (PLFA) compositions. PLFA content was always less than 5% of dry weight, but NLFA content varied from 5.9% to 29.6% of dry weight, depending upon species. Combined C(20) PUFA proportions of up to 9.2% and 48% were observed in the NLFA and PLFA fractions, respectively, resulting in total C(20) PUFA proportions of up to 19.4% of the total fatty acid compositions of Collembola. C(20) PUFAs were also detected in Collembola specimens from a deciduous woodland at proportions up to 29.7% of the total fatty acid composition. Terrestrial invertebrates generally contain <4% and <22% C(20) PUFAs in PLFAs and NLFAs, respectively; therefore, these results demonstrate that Collembola often possess the highest proportions of C(20) PUFAs yet observed in terrestrial invertebrates. The biochemical reasons for such high C(20) PUFA proportions, which were biosynthesised by the Collembola since these components were absent from the yeast diets, remain unclear. The distinctive fatty acid compositions of Collembola may be useful in soil food web studies utilising fatty acids as biomarkers of trophic behaviour.

Lipid content and carbon assimilation in Collembola: implications for the use of compound-specific carbon isotope analysis in animal dietary studies

In an effort to understand the relationships between both the lipid content and delta13C values of Collembola and their diet, isotopically labelled (C3 and C4) bakers' yeasts were cultured and fed to two Collembolan species, Folsomia candida and Proisotoma minuta. The fatty acid composition of Collembola generally reflected that of the diet with the addition of the polyunsaturated components 18:2(n-6), 20:4(n-6) and 20:5(n-3), which appeared to be biosynthesised by the Collembola. Whilst ergosterol was the only sterol detected in the yeast diets, only cholesterol was detected in Collembola, and although the delta13C values of diet and consumer sterols differed by >2 per thousand, the delta13C values indicated that cholesterol was derived entirely from dietary sterol. The bulk delta13C values of Collembola were similar to those of the diets, but fatty acid delta13C values did not necessarily reflect those of the dietary fatty acids, indicating significant de novo biosynthesis of fatty acids within Collembola. Switching the Collembola from C3 to C4 yeast enabled the determination of the rates of incorporation of dietary carbon into Collembolan lipids, and showed that half-lives of the incorporation of dietary carbon varied between 1.5 and 5.8 days at 20 degrees C. Cholesterol exhibited the slowest rate of incorporation in both species, while bulk carbon in F. candida possessed an intermediate rate. These results demonstrate that an understanding of the sources of isotopic fractionation and the role of biochemistry in regulating the delta13C values of individual compounds is important in the application of compound-specific isotopic analysis to the study of animal trophic activities.

Effects of gamma irradiation on Holcus lanatus (Yorkshire fog grass) and associated soil microorganisms

An investigation was conducted to determine the impact of acute doses of gamma radiation on the microbial community structure of a Holcus lanatus dominated grassland soil. Mesocosms containing soil and established grass were irradiated using a sealed (137)Cs source (7.0 Gy min(-1)). Doses ranged from 5 to 160 Gy, analyses were conducted on the day of irradiation, then 7 and 30 days later. Plant growth and arbuscular mycorrhizal fungal colonisation of roots were reduced by irradiation. Gram-negative bacteria, and microbial metabolic capacity were also negatively affected by treatment. Microbial biomass measured by phospholipid fatty acid (PLFA) analysis, showed an increase at doses above 20 Gy, 7 and 30 days after treatment. Proportions of Gram-positive bacterial and fungal PLFAs fluctuated inversely to each other, in response to both sampling time and radiation dose. We hypothesise that many of the observed soil microbial responses are indirect effects mediated by the influence of ionising radiation on the plants in this system.

Retained cocaine conditioned place preference in D1 receptor deficient mice

The role of the D1 dopamine receptor subtype in mediating cocaine effects was examined in mice in which the D1 receptor gene had been ablated by homologous recombination. Cocaine reward was assessed by conditioned place preference experiments using mice which had either one allele (+/-) or both alleles (-/-) of the D1 dopamine receptor gene disrupted and in their wild type (+/+) littermates. Cocaine conditioning resulted in similar increases in preference for drug-paired environments in mice of each of the three genotypes. Cocaine did not alter locomotor activity levels in homozygous, D1 knockout mice -/-, whereas increased activity was noted in both +/+ and +/- animals. These results are consistent with the idea that the D1 receptor is involved in the locomotor stimulant effects of cocaine, but has little role in a major test of the rewarding and reinforcing effects of the drug.