MidKent College

Abstract Aquatic invasive species, such as the signal crayfish (Pacifastacus leniusculus), present a major threat to freshwater ecosystems. However, these species can be challenging to detect in recently invaded habitats. Environmental DNA (eDNA)–based methods are highly sensitive and capable of detecting just a few copies of target DNA from non‐invasively collected samples. Therefore, they have considerable potential for broad‐scale use in mapping and monitoring the spread of invasive species. In this study, we aimed to increase our understanding of the current distribution of signal crayfish in a headwater stream system in the United Kingdom (tributaries of the River Wharfe, Addingham, Yorkshire). Environmental DNA sampling, assessment of water chemistry variables, and conventional crayfish hand‐searching were conducted across 19 study sites in five tributary streams. Using hand‐searching, we detected signal crayfish at 26% of the sites (5/19 study sites). However, using eDNA‐based methods, occupancy increased to 47% of study sites (9/19). Our sampling revealed previously unknown sites of crayfish occupancy, and using eDNA‐based methods, we were able to define the geographical extent of the invasion front in each headwater stream sampled. This study highlights that eDNA‐based methods are well‐suited for detecting newly established signal crayfish populations in recently invaded habitats, even when the invasive species is at low abundance and, therefore, might otherwise be under‐represented or undetected using conventional survey methods. Our study provides further evidence that headwater stream ecosystems are particularly vulnerable to signal crayfish invasion. However, their geomorphological features may make methods used to reduce or prevent invasive crayfish dispersal more effective than in other freshwater ecosystems.

As part of a European Union project (FAIR CT97 3020) microwave dielectric spectra of processed prawns (Pandalus borealis), cod (Gadus morhua), pork and chicken were measured and the data transformed using the statistical method of principal component analysis. The principal components were regressed (principal component regression) against various compositional variables, notably added water, protein, water, total phosphorus and NaCl and the calibration was validated using the method of internal cross-validation.

Bacteriophage A7 has been employed as an indicator for strains of Pseudomonas syringae pv. morsprunorum race 1. Electron microscopy showed that this phage had a hexagonal head, 59 nm in diameter, and a long, flexible, non-contractile tail, 164 nm long and 8 nm wide, containing approximately 15 evenly spaced transverse striations and terminating in a base-plate equipped with six spikes arranged in a radially symmetrical pattern around a central core. Two short fibres projecting at an angle from the base-plate were also visible on some phage particles. Phage A7 can therefore be placed in group B of the classification system of Bradley. Phage particles bound at apparently random sites over the surface of host cells by their base-plates, and after a short time released DNA from their heads. Phage A7 uses lipopolysaccharide (LPS) as its binding site on the bacterial cell surface, removing the d-rhamnan side-chains by the action of a rhamnan hydrolase. The appearance of purified LPS by electron microscopy was either strand-like or vesicular, according to whether it had been stained with phosphotungstate or uranyl acetate respectively. Strands were of approximately uniform width (approx. 9 nm). Vesicular forms included both circles, 25–45 nm in diameter, and larger oval structures of greater electron transparency. The appearance of the LPS did not alter on addition of the phage. Phage particles were observed attached via their base-plates to LPS vesicles, in particular the larger oval vesicles, but were never seen attached to strands. The heads of phage particles attached to LPS were frequently empty. The rhamnanase of phage A7 released the side-chain residues from the LPS as an equimolar mixture of tri- and hexasaccharide. By using 1 h-NMR spectroscopy and methylation analysis, the site of cleavage has been identified as the 2)-α-d-Rhap(1 → 3) residue.

Abstract Using either1l0m Ag-labelled Agl or labelled 0.02 M AgN03 solution, the kinetics of the exchange between the solid and Ag+ ions in solution exhibited a fast initial stage, possibly involving a surface layer of the solid, followed by a slower exchange possibly with Ag+ ions in the lattice. The initial rate increased as the solid/solution ratio increased but this rate was not appreciably altered when the solid was irradiated with visible light prior to the experiment. However, this treatment led to an increase in the rate of the slower step compared to that found for the solid which was not irradiated. The same trend was observed for the solid which was heated before the experiment above the transition temperature to the α-form.