Genetic methods for the detection of microbial pathogens. Identification of enterotoxigenic Escherichia coli by DNA colony hybridization: collaborative study

Enteropathogenic Escherichia coli strains may produce a cholera-like, heat-labile enterotoxin (LT) as a virulence factor. The gene that codes for LT can be purified by recombinant DNA techniques and used as a genetic probe for DNA hybridization. These probes detect enterotoxigenic strains as well as strains that may not manifest toxin production but carry the genetic information to do so. In this study, 13 laboratories tested 3 known and 25 unknown (10 positive and 15 negative) cultures of E. coli for the presence of the LT gene. The isolates had been tested and classified by the mouse Y-1 adrenal cell test and an enzyme-linked immunosorbent assay. Cultures were spotted on nitrocellulose filters on MacConkey agar and incubated. Colonies were lysed in situ and their DNA was hybridized to 32P-labeled, purified LT gene DNA (provided to the collaborators). Positive colonies were identified by autoradiography. Of 325 samples, 315 (96.9%) were identified correctly and 10 were misclassified; there were 6 false negative and 4 false positive identifications. Chi-square values indicated that the method agreed with the previous classification and was equally efficient in distinguishing positive and negative samples (95.7 and 98.1%, respectively). The method has been adopted official first action.     

The profitability of producing channel catfish Ictalurus punctatus (Rafinesque) in cages at a commercial scale on small farms

Past beneficiaries of research and extension projects in aquaculture in the USA have been large farmers using pond culture systems. Additional studies, based on sound knowledge of empirical behaviour, are needed to identify alternative technologies and aid in the management decisions of small-scale farms. A mixed integer, multiperiod linear programming model and survey data were used to analyse the profitability of caged channel catfish, Ictalurus punctatus (Rafinesque), culture. Results suggest that only a limited number of farmers may be able to adopt cage culture as an alternative farm enterprise. Profitability was sensitive to assumed product prices.     

Contrasting climate velocity impacts in warm and cool locations show that effects of marine warming are worse in already warmer temperate waters

Species responses to climate change are often measured at broad spatiotemporal scales, which can miss the fine-scale changes that are most relevant to conservation and fisheries management. We develop a scaleable geostatistical approach to assess how juvenile and adult fish distributions have been shaped by changes in bottom temperature and dissolved oxygen over a recent decade of warming in the northeast Pacific. Across 38 demersal fishes, biomass trends were associated negatively with warming and positively with dissolved oxygen, but when trends in both biomass and climate were converted to velocities—the speed and direction a population would have to move to maintain consistent conditions—the effect of temperature change differed depending on local conditions. In the warmest locations, warming velocities were associated with negative biotic velocities for 19 of 69 species-maturity combinations, and yet were almost always associated with stable or positive biotic velocities in the coolest locations (64 of 69). These spatially consistent biomass declines (negative biotic velocities) in the warmest locations and increases in cooler locations suggest a redistribution of species with the potential for new ecological and fisheries interactions. After controlling for temperature, the more spatially consistent effects of dissolved oxygen were often negative, suggesting a mechanism other than hypoxia avoidance—potentially changes in primary production. Our approach identifies the species and locations that are most sensitive to observed changes in the environment at any scale, thus facilitating future vulnerability assessments.     

Effects of organic matter in aquacultural waste on the ammonium exchange capacity of clinoptilolite

Clinoptilolite, an ammonium-selective ion exchanger, is being used to control ammonia accumulation in recirculating culture systems. Studies were conducted to establish a correlation among the ammonium exchange capacity of clinoptilolite, level of organic matter in aquacultural wastewater, and regenerant solution type. A recirculating culture system of 2300-I capacity provided wastewater with a represantative organic matrix. Treatment of the wastewater led to a decrease in the performance of clinoptilolite under non-equilibrium (packed-column) and equilibrium operating conditions. The extent of the effects increased with an increase in organic level of the treatment solution. In packed-column tests, the maximum observed reductions in mean removal efficiency (3.5%), volume of wastewater treated prior to reaching breakthrough (14.9%), and operating exchange capacity (19.7%), occurred in columns regenerated with a brine of pH 7.0. Columns regenerated with a brine of pH 10.5 showed little response. Treatment of aquacultural wastewater produced a brown discoloration of the packing which was removed by treatment with 1 bed volume of a hypochlorite restorant solution (0.5% Cl₂).     

Plant litter decomposition and microbial characteristics in volcanic soils (Mt Etna,Sicily) at different stages of development

Soils at different developmental stages were sampled from eight sites on the slopes of Mt Etna, Sicily (Italy) and characterized for total C, microbial biomass and microbial respiration. The values of these parameters were greatest for the most developed soils, but differences in recent management and site characteristics limited analysis of trends with soil development across the eight sites. The decomposition kinetics of both intact leaf litter and the water-insoluble fraction of leaf litter from three common species on Etna [Etnean broom (Genista aetnensis), European chestnut (Castanea sativa), and Corsican pine (Pinus nigra)] were determined in four of the soils (the two with the smallest and the two with the largest organic C contents) in a laboratory experiment over 168 days to test two hypotheses. First, that the readily mineralized fraction of added plant C is greater when the plant material decomposes in well-developed soils compared to less developed soils, and second, that the microbial communities in less developed soils are less efficient at mineralizing C from low quality plant residues. The first hypothesis held for Genista and Pinus litter, but not Castanea litter. The second hypothesis was supported for the Castanea and Pinus litter, but not for the Genista litter. Thus, the general applicability of the hypotheses was dependent on the precise source and characteristics of the litter.     

Quantification,Morphology and Ultrastructure of Preantral Follicles of Buffalo (Bubalus bubalis) Foetuses

The objective of this study was to determine the number, morphology and ultrastructure of preantral ovarian follicles of buffalo (Bubalus bubalis) foetuses at different ages. Quantification revealed number of primordial, primary and secondary follicles of 48 857 ± 17 506, 26 000 ± 20 452, 18 428 ± 10 875 and 18 375 ± 19 690, 225 ± 349, 326 ± 288 at 12–34 cm and 35–60 cm crown rump length (CRL), respectively. Follicular diameter values were 28.9 (±3.4), 34.7 (±5.9) and 59.4 (±12.6) μm; oocyte diameters were 21.7 (±2.8), 24.3 (±3.4) and 33.0 (±7.7) μm, and the numbers of follicular cells in the follicle equatorial section were 7.1 (±1.4), 12.0 (±2.4) and 13.8 (±2.4) for primordial, primary and secondary follicles, respectively. The primordial follicle consisted of an oocyte surrounded by a layer of flattened follicular cells with a normally eccentric oocyte nucleus. Dispersed Golgi complex, smooth endoplasmic reticulum, rounded mitochondria and several lipid vesicles were observed in the cytoplasm and cell junctions between the follicle cell membranes and the oocyte. This work describes the number, morphometry and ultrastructure of preantral follicles of buffalo foetuses, concluding that folliculogenesis is established between 8 and 34 cm CRL and that follicle number varies individually and according to age and that further studies are needed in this species.