Comparison of spontaneous antibiotic resistance frequency of Salmonella Typhimurium growth in glucose amended continuous culture at slow and fast dilution rates

The objective of the study was to determine the frequency of spontaneous acquisition of resistance to select antibiotics by Salmonella Typhimurium (ST) when grown in glucose amended continuous flow culture at slow (D = 0.025 h(-1)) or fast (D = 0.27 h(-1)) dilution rates. The bacterium was grown in LB minimal medium (pH 6.25) containing no antibiotics. Upon achieving steady state, samples were plated to tryptic soy agar (TSA) alone or supplemented (per ml) with 2 and 16 microg oxytetracycline, 4 and 16 microg tetracycline, 2 and 64 microg kanamycin, and 0.25 and 2 microg enrofloxacin. Regardless of growth rate, CFU of resistant ST from the TSA containing antibiotics was less than 2 x 10(1) except for 2 microg kanamycin and 0.25 microg enrofloxacin treatments (higher than 1 x 10(9) and 4 x 10(7) CFU of resistant ST for trials 1 and 2, respectively). Frequency of recovering resistant ST from the TSA containing the higher antibiotic concentrations was less than 1 in 10(9) for all antibiotics, but was higher on the media containing 2 microg kanamycin and 0.25 microg enrofloxacin at both slow and fast growth rates. In general, minimal susceptibility differences were detected for isolates from slow and fast dilution rates.     

Growth of zooxanthellae in culture with two nitrogen sources

Physiological characteristics of zooxanthellae were examined under nutrient-saturated conditions created by mixing ammonium (¹⁵NH₄) with nitrate (¹⁵NO₃) to give 0.88 mM total nitrogen. Growth rate varied with the form of nitrogen provided. Ammonium alone resulted in the lowest C:N and C:chl-a ratios. Although zooxanthellae took up nitrate in the absence of ammonium, ammonium assimilation was 1.3 times higher than nitrate assimilation. Ammonium strongly inhibited nitrate assimilation. While high-ammonium treatments resulted in the highest ¹⁴C incorporation into intermediate compounds, high nitrate levels resulted in the highest ¹⁴C incorporation into protein, suggesting that the intermediate compounds are produced prior to the subsequent production of protein when ammonium is the dominant N source. The enhanced production of intermediate compounds at the expense of carbon directed to protein synthesis in the presence of ammonium might be analogous to the “host factor” observed in zooxanthellae–host symbioses, since growth rate is depressed due to low production of protein. Received: 16 March 2000 / Accepted: 26 August 2000     

ANALYSIS AND MODELING OF LONG-TERM STREAM TEMPERATURES ON THE STEAMBOAT CREEK BASIN,OREGON: IMPLICATIONS FOR LAND USE AND FISH HABITAT1

ABSTRACT: Steamboat Creek basin is an important source of timber and provides crucial spawning and rearing habitat for anadromous steelhead trout (Oncorhynchus mykiss). Because stream temperatures are near the upper limit of tolerance for the survival of juvenile steelhead, the possible long-term effect of clear-cut logging on stream temperatures was assessed. Twenty-year (1969–1989) records of summer stream temperature and flow from four tributaries and two reaches of Steamboat Creek and Boulder Creek (a nearby unlogged watershed) were analyzed. Logging records for the Steamboat Creek basin and air temperature records also were used in the analysis. A time-series model of the components of stream temperature (seasonal cycle of solar radiation, air temperature, streamflow, an autoregressive term of order 1, and a linear trend variable) was fitted to the water-temperature data. The linear trend variable was significant in all the fitted models except Bend Creek (a tributary fed by cool ground-water discharge) and Boulder Creek. Because no trends in either climate (i.e., air temperature) or streamflow were found in the data, the trend variable was associated with the pre-1969 loss and subsequent regrowth of riparian vegetation and shading canopies.     

Operating Experience with Biogas Plants in Sri Lanka

Three hundred and three biogas plants, representing a majority of the units installed in Sri Lanka up to 1984, were inspected, and it was found that 280 of these had been put into commission at some time prior to the study. Of the 280 commissioned plants, 170 (61%) were functioning satisfactorily providing biogas for cooking and/or lighting. The remaining 110 (39%) were either not functioning or were supplying very little gas owing to gas leaks, inadequate input of dung, or poor plant management. The most common plant was the 6 m³, fixed dome, household plant, and the most common raw material used was cattle dung. In the majority of household plants the cost of construction was partly or wholly subsidized.     

RESPONSE OF NORTH AMERICAN FRESHWATER LAKES TO SIMULATED FUTURE CLIMATES1

ABSTRACT: We apply a physically based lake model to assess the response of North American lakes to future climate conditions as portrayed by the transient trace-gas simulations conducted with the Max Planck Institute (ECHAM4) and the Canadian Climate Center (CGCM1) atmosphere-ocean general circulation models (A/OGCMs). To quantify spatial patterns of lake responses (temperature, mixing, ice cover, evaporation) we ran the lake model for theoretical lakes of specified area, depth, and transparency over a uniformly spaced (50 km) grid. The simulations were conducted for two 10-year periods that represent present climatic conditions and those around the time of CO₂ doubling. Although the climate model output produces simulated lake responses that differ in specific regional details, there is broad agreement with regard to the direction and area of change. In particular, lake temperatures are generally warmer in the future as a result of warmer climatic conditions and a substantial loss (> 100 days/yr) of winter ice cover. Simulated summer lake temperatures are higher than 30°C over the Midwest and south, suggesting the potential for future disturbance of existing aquatic ecosystems. Overall increases in lake evaporation combine with disparate changes in A/OGCM precipitation to produce future changes in net moisture (precipitation minus evaporation) that are of less fidelity than those of lake temperature.     

Phosphorus leaching from biosolids-amended sandy soils

Increasing emphasis on phosphorus (P)-based nutrient management underscores the need to understand P behavior in soils amended with biosolids and manures. Laboratory and greenhouse column studies characterized P forms and leachability of eight biosolids products, chicken manure (CM), and commercial fertilizer (triple superphosphate, TSP). Bahiagrass (Paspalum notatum Flugge) was grown for 4 mo on two acid, P-deficient Florida sands, representing both moderate (Candler series: hyperthermic, uncoated Typic Quartzipsamments) and very low (Immokalee series: sandy, siliceous, hyperthermic Arenic Alaquods) P-sorbing capacities. Amendments were applied at 56 and 224 kg P(T) ha(-1), simulating P-based and N-based nutrient loadings, respectively. Column leachate P was dominantly inorganic and lower for biosolids P sources than TSP. For Candler soil, only TSP at the high P rate exhibited P leaching statistically greater (alpha = 0.05) than control (soil-only) columns. For the high P rate and low P-sorbing Immokalee soil, TSP and CM leached 21 and 3.0% of applied P, respectively. Leachate P for six biosolids was <1.0% of applied P and not statistically different from controls. Largo biosolids, generated from a biological P removal process, exhibited significantly greater leachate P in both cake and pelletized forms (11 and 2.5% of applied P, respectively) than other biosolids. Biosolids P leaching was correlated to the phosphorus saturation index (PSI = [Pox]/[Al(ox) + Fe(ox)]) based on oxalate extraction of the pre-applied biosolids. For hiosolids with PSI < or = approximately 1.1, no appreciable leaching occurred. Only Largo cake (PSI = 1.4) and pellets (PSI = 1.3) exhibited P leaching losses statistically greater than controls. The biosolids PSI appears useful for identifying biosolids with potential to enrich drainage P when applied to low P-sorbing soils.     

Animal Agriculture: Symbiosis, Culture, or Ethical Conflict?

Several writers on animal ethics defend the abolition of most or all animal agriculture, which they consider an unethical exploitation of sentient non-human animals. However, animal agriculture can also be seen as a co-evolution over thousands of years, that has affected biology and behavior on the one hand, and quality of life of humans and domestic animals on the other. Furthermore, animals are important in sustainable agriculture. They can increase efficiency by their ability to transform materials unsuitable for human consumption and by grazing areas that would be difficult to harvest otherwise. Grazing of natural pastures is essential for the pastoral landscape, an important habitat for wild flora and fauna and much valued by humans for its aesthetic value. Thus it seems that the environment gains substantially when animals are included in sustainable agricultural systems. But what about the animals themselves? Objections against animal agriculture often refer to the disrespect for animals’ lives, integrity, and welfare in present intensive animal production systems. Of the three issues at stake, neither integrity nor animal welfare need in principle be violated in carefully designed animal husbandry systems. The main ethical conflict seems to lie in the killing of animals, which is inevitable if the system is to deliver animal products. In this paper, we present the benefits and costs to humans and animals of including animals in sustainable agriculture, and discuss how to address some of the ethical issues involved.     

The current practice of health risk assessment: potential impact on standards for toxic air contaminants

Since the Bhopal incident, the public has placed pressure on regulatory agencies to set community exposure limits for the dozens of chemicals that may be released by manufacturing facilities. More or less objective limits can be established for the vast majority of these chemicals through the use of risk assessment. However, each step of the risk assessment process (i.e., hazard identification, dose-response assessment, exposure assessment, and risk characterization) contains a number of pitfalls that scientists need to avoid to ensure that valid limits are established. For example, in the hazard identification step there has been little discrimination among animal carcinogens with respect to mechanism of action or the epidemiology experience. In the dose-response portion, rarely is the range of "plausible" estimated risks presented. Physiologically based pharmacokinetic (PB-PK) models should be used to understand the difference between the tissue doses and the administered dose, as well as the difference in target tissue concentrations of the toxicant between rodents and humans. Biologically-based models like the Moolgavkar-Knudson-Venzon (MKV) should be developed and used, when appropriate. The exposure assessment step can be significantly improved by using more sensitive and specific sampling and analytical methods, more accurate exposure parameters, and computer models that can account for complex environmental factors. Whenever possible, model predictions of exposure and uptake should be validated by biological monitoring of exposed persons (urine, blood, adipose) or by field measurements of plants, soil, fish, air, or water. In each portion of an assessment, the weight of evidence approach should be used to identify the most defensible value. In the risk characterization, the best estimate of the potential risk as well as the highest plausible risk should be presented. Future assessments would be much improved if quantitative uncertainty analyses were conducted. Procedures are currently available for making future assessments. By correcting some of these shortcomings in how health risk assessments have been conducted, scientists and risk managers should be better able to identify scientifically appropriate ambient air standards and emission limits.     

Combined use of eDNA metabarcoding and video surveillance for the assessment of fish biodiversity

Monitoring communities of fish is important for the management and sustainability of fisheries and marine ecosystems. Baited remote underwater video systems (BRUVs) are among the most effective nondestructive techniques for sampling bony fishes and elasmobranchs (sharks, rays, and skates). However, BRUVs sample visually conspicuous biota; hence, some taxa are undersampled or not recorded at all. We compared the diversity of fishes characterized using BRUVs with diversity detected via environmental DNA (eDNA) metabarcoding. We sampled seawater and captured BRUVs imagery at 48 locales that included reef and seagrass beds inside and outside a marine reserve (Jurien Bay in Western Australia). Eighty-two fish genera from 13 orders were detected, and the community of fishes described using eDNA and BRUVs combined yielded >30% more generic richness than when either method was used alone. Rather than detecting a homogenous genetic signature, the eDNA assemblages mirrored the BRUVs’ spatial explicitness; differentiation of taxa between seagrass and reef was clear despite the relatively small geographical scale of the study site (∼35 km²). Taxa that were not sampled by one approach, due to limitations and biases intrinsic to the method, were often detected with the other. Therefore, using BRUVs and eDNA in concert provides a more holistic view of vertebrate marine communities across habitats. Both methods are noninvasive, which enhances their potential for widespread implementation in the surveillance of marine ecosystems.