Probing the chiroptical response of a single molecule

Chirally sensitive measurement techniques have generally been restricted to bulk samples. Here, we report the observation of fluorescence-detected circular dichroism (FDCD) from single (bridgedtriarylamine) helicene molecules by using an excitation wavelength (457 nanometers) in the vicinity of an electronic transition that shows circular dichroism in bulk samples. The distributions of dissymmetry (g) parameters by analysis of signals from pure M- and P-type diastereomers are almost perfect mirror images of one another, each spanning a range of both positive and negative values. In addition, we observe a well-defined structure in the histogram of dissymmetry parameters suggestive of specific molecular orientations at the polymer interface. These single-molecule results highlight strong intrinsic circular dichroism responses that can be obscured by cancellation effects in ensemble measurements of a randomly oriented bulk sample.     

A case study of biofilter activation and microbial nitrification in a marine recirculation aquaculture system for rearing Atlantic salmon (Salmo salar L.)

Marine recirculation aquaculture system (RAS) is a prominent technology within fish farming. However, the nitrifying bacteria in the biofilter have low growth rates, which can make the biofilter activation a long and delicate process with periods of low nitrification rates and variations in water quality. More knowledge on the microbial development in biofilters is therefore needed in order to understand the rearing conditions that favour optimal activation of the biofilters. In this case study, we investigated the activation of two biofilters in a marine RAS for Atlantic salmon post‐smolt associated with either high or low stocking densities of fish by monitoring the microbial communities and chemical composition. The results showed that the microbial communities in both biofilters were similar during the first rearing cycle, despite variations in the water quality. Nitrifying bacteria were established in both biofilters; however, the biofilter associated with low stocking density had the highest relative abundance of ammonia‐oxidizing Nitrosococcus (1.0%) and nitrite‐oxidizing Nitrospira (2.1%) at the end of the first rearing cycle, while the relative abundance of ammonia‐oxidizing Nitrosomonas (2.3%–2.9%) was similar in both biofilters. Our study showed that low fish stocking density during the first rearing cycle provided low and steady concentrations of ammonium, nitrite and organic load, which can stimulate rapid development of a nitrifying population in new marine RAS biofilters.     

Structure of the advanced regeneration community in tropical rain forest fragments of Los Tuxtlas, Mexico

We characterized the tree seedling community within seven forest fragments of different size (3-640 ha) at Los Tuxtlas, Mexico. We considered individual density, species richness, diversity, composition and functional group (shade tolerant, non-pioneer-light demander and pioneer species). We recorded 8038 individuals, belonging to 128 species and 40 morphospecies. Overall, shade-tolerant species had the highest density and diversity followed by non-pioneer-light demanders and pioneer species. Mean individual density per plot was not related to fragment size, but mean species richness per plot, total observed species richness and diversity were inversely related to fragment size, with the smallest fragments having the highest values. Species composition comparisons highlighted low similarity among fragments. Furthermore, larger fragments shared more species with the smallest fragments than between each other. Our results show that the largest fragments do not always hold the highest species richness; that small fragments comprise of high seedling species diversity, and represent a high regeneration potential for tree native species in the study landscape.     

High levels of spatial heterogeneity in the biodiversity of soil prokaryotes on Signy Island, Antarctica

In a previous study, soil bacterial diversity at environmentally distinct locations on Signy Island was examined using denaturing gradient gel electrophoresis (DGGE) profiling, and a range of chemical variables in soils was determined in order to describe variations between them. The dominant bacterial communities of all locations were found to be significantly different, although higher levels of similarity were observed between locations with similar physico-chemical characteristics, such as at penguin rookeries, seal wallows and vegetated soils. Extending this study, here soil prokaryote biodiversity was compared between 15 distinct locations in order to elucidate any interaction between four general habitat types on Signy Island (South Orkney Islands, maritime Antarctic) and any influence of previous human impacts at these sites. Specific sites were selected to represent the range of different soil environments present and to cover a range of environmental factors present in the maritime Antarctic which are known to influence bacterial community composition in soils elsewhere. A diverse prokaryote community is described, again with the majority of excised and sequenced bands belonging to the Bacteroidetes. Although DGGE profiling identified significant differences in prokaryotic biodiversity between all sampling sites, aggregations of banding patterns were also apparent across the different soil environments examined. Correlations between specific DGGE profiles and 10 selected soil parameters suggested that much of this variation could be explained by differences in the levels of environmental disturbance and soil pH. In particular, a greater proportion of variation in soil bacterial diversity was explained by differences in soil properties at human-disturbed locations than at undisturbed locations, with higher explanatory values by edaphic factors in the former and soil metal content in the later. In general, our data indicate that small-scale variation is an important factor in understanding patterns of prokaryotic distributions in soil habitats in the maritime Antarctic environment.     

Farmer perspectives and practices regarding water pollution control programmes in Scotland

Nitrate Vulnerable Zones (NVZ) were introduced in response to the Nitrates Directive (91/676/EEC) which states that all EU countries must reduce the nitrate in drinking water to a maximum of 50 mg/l. Farmers within a designated NVZ must adhere to strict rules over the timing and application of nitrogen from organic and inorganic sources. In Scotland, four NVZ regions were designated in 2003, covering around 14% of the land area and affecting over 12,000 farmers.This paper outlines the results of a recent study to understand farmer activities in response to and attitudes towards NVZ regulations in Scotland. A telephone survey was administered, obtaining a response of 184 farmers, supplemented by four workshops held in each NVZ region. This explored, both quantitatively and qualitatively, farmer behaviour and attitudes.The bulk of farmers have made little capital investment since the 2003 designation. Few farmers have invested in increased slurry storage facilities, nor begun to transport more slurry off-farm, claiming to have had enough storage capacity before designation to cover the imposed closed period.Farmer attitudes indicate a mostly negative view towards the perceived environmental benefits, water management and compliance. This can be explained by a number of concerns raised by farmers towards the scientific basis for designations. Furthermore, farmers viewed the restrictions placed on farming practices within NVZs as too inflexible.Given the mostly sceptical perceptions demonstrated by the farmers we call for a more integrated approach to water management at the catchment level. There is a role for policy-makers to provide clearer information over the science and purpose of the designations and also to invest in the transfer of technologies, in particular N-use software which is specifically tailored to NVZ regulations. Also, critical to this would be the development of transparent indicators of water quality. This may start to embed nitrogen pollution impacts within the farmer's cultural framework of decision-making.     

Infection of cotton byfusarium oxysporum f.sp.vasinfectum as affected by water stress

Since virulence ofFusarium oxysporum f.sp.vasinfectum (FOV) on cotton (Gossypium hirsutum) is enhanced when the fungus is cultivated in a saline environment, excessively saline water must not be used for the irrigation of cotton. However, the limitations thus placed on the available water resources may lead to conditions of enforced water stress for the plant. The present study investigated whether water stress affects the susceptibility of cotton to FOV. Groups of 2-month-old cotton plants of theFusarium-susceptible Coker 304 and the moderately resistant GSC 20 varieties were maintained without watering for varying periods immediately before or after being inoculated with FOV (15 plants per group, two replications). Watering was suspended for 3, 6, 12 or 24 days before inoculation, and for 3, 6, 12 or 15 days after inoculation. After inoculation the plants were maintained in a controlled environment with a 15,000 lux, 12-h photoperiod, at 28°/24°C D/N, 20% r.h. Xylem water potential was determined in a pressure chamber. Percent infected leaf area and date of onset of wilt were the parameters used to define severity of FOV infection. There was a consistent relation between low water potential in the xylem (-7 and -20 MPa) and severity of infection, particularly when the dry period occurred after inoculation. After exposure to the lowest post-inoculation water potentials, even variety GSC 20, which is normally moderately resistant, exhibited a fairly high percent infected leaf area. This should be taken into account when the cotton grower is faced with water shortages, especially during the period from branching to flower bud break.     

Interspecific competition and rarity in mudsnails: feeding interactions between and within Hydrobia acuta neglecta and sympatric Hydrobia species

• 1. Using production of faecal pellets as a proxy for feeding rate, possible reciprocal effects of the widespread and abundant mudsnails Hydrobia ulvae and Hydrobia ventrosa on the rare Hydrobia acuta neglecta were investigated under the sea‐water salinity conditions in which all three species occur naturally in East Anglia, UK.
• 2. Over a density range equivalent to 1000–34 000 m^?2, H. acuta and H. ventrosa (though not H. ulvae) at some point displayed an intraspecific reduction in egestion with increase in density. For H. acuta, every 5000 extra snails above a threshold of 16 000 m^?2 reduced egestion by up to 8%; and for H. ventrosa, every 5000 extra snails above a threshold of 8000 m^?2 reduced egestion by an average 7%.
• 3. Keeping the density of one test species constant at 4000 m^?2 whilst varying that of a sympatric one from 0 up to 30 000 m^?2 indicates that H. ulvae has a marked effect on H. acuta at all densities, decreasing its egestion by 10% for every 5000 m^?2 H. ulvae also present, but that H. acuta has no such reciprocal effect on H. ulvae. H. ventrosa had no effect on egestion in H. acuta, although H. acuta did have some minor effect on H. ventrosa, on average decreasing its egestion by 3% for every 5000 m^?2 H. acuta present.
• 4. The intensity of intraspecific competition within H. acuta, therefore, exceeds that exerted on H. acuta by H. ventrosa, and likewise intraspecific effects within H. ventrosa generally outweigh any interspecific effect from H. acuta. The effect of H. ulvae on H. acuta, however, exceeds that intraspecifically within H. acuta.
• 5. These results are discussed in relation to the rarity of H. acuta neglecta.

Copyright © 2005 John Wiley & Sons, Ltd.