Immunohistochemical Characterization of Sarcomas in Trp53+/- Haploinsufficient Mice.

The use of immunohistochemical (IHC) staining in determining and/or confirming the cellular origin of poorly differentiated sarcomas was evaluated in this study. Sarcomatous neoplasms were evaluated in a research study conducted in 2 strains of p53+/- haploinsufficient mice. The most common neoplasms were undifferentiated sarcomas, followed by osteosarcomas and rhabdomyosarcomas (RMSs). The RMSs were poorly differentiated and appeared similar to the pleomorphic, or adult type, RMS of humans. All sarcomas stained positive by IHC for the mesenchymal cell intermediate filament vimentin. The RMSs were identified by positive IHC staining for myogenin, a transcription factor specific to skeletal muscle. Osteosarcomas were easily identifiable on hematoxylin and eosin-stained slides; no generally accepted IHC stain specific for bone is presently available. Some of the undifferentiated sarcomas contained numerous macrophages that stained positive for F4/80, a macrophage marker; the positive-staining cells were considered to be infiltrating macrophages. One-third of the neoplasms observed in this study were associated with subcutaneous implanted electronic microchips used for animal identification. Based upon histopathologic evaluation and IHC staining, it was not possible to distinguish neoplasms associated with subcutaneous microchips from neoplasms not associated with microchips.

Characterization of skin abnormalities in a mouse model of osteogenesis imperfecta using high resolution magnetic resonance imaging and Fourier transform infrared imaging spectroscopy.

Evaluation of the skin phenotype in osteogenesis imperfecta (OI) typically involves biochemical measurements, such as histologic or biochemical assessment of the collagen produced from biopsy-derived dermal fibroblasts. As an alternative, the current study utilized non-invasive magnetic resonance imaging (MRI) microscopy and optical spectroscopy to define biophysical characteristics of skin in an animal model of OI. MRI of skin harvested from control, homozygous oim/oim and heterozygous oim/+ mice demonstrated several differences in anatomic and biophysical properties. Fourier transform infrared imaging spectroscopy (FT-IRIS) was used to interpret observed MRI signal characteristics in terms of chemical composition. Differences between wild-type and OI mouse skin included the appearance of a collagen-depleted lower dermal layer containing prominent hair follicles in the oim/oim mice, accounting for 55% of skin thickness in these. The MRI magnetization transfer rate was lower by 50% in this layer as compared to the upper dermis, consistent with lower collagen content. The MRI transverse relaxation time, T2, was greater by 30% in the dermis of the oim/oim mice compared to controls, consistent with a more highly hydrated collagen network. Similarly, an FT-IRIS-defined measure of collagen integrity was 30% lower in the oim/oim mice. We conclude that characterization of phenotypic differences between the skin of OI and wild-type mice by MRI and FT-IRIS is feasible, and that these techniques provide powerful complementary approaches for the analysis of the skin phenotype in animal models of disease.

Useful immunohistochemical markers of tumor differentiation.

Immunohistochemistry (IHC) has been somewhat underutilized in the practice of toxicological pathology but can be a valuable tool for the evaluation of rodent neoplasms, both in a diagnostic and an investigational role. Determining an exact tumor type using standard hematoxylin and eosin (H&E) staining of formalin-fixed tissues can be challenging, especially with metastatic and/or poorly differentiated tumors. Successful IHC is dependent on many factors, including species and tissue type, type and duration of fixation, quality fresh or frozen sectioning, and antibody specificity. The initial approach of most tumor diagnosis IHC applications is distinguishing epithelial from mesenchymal differentiation using vimentin and cytokeratin markers, although false-negative and/or false-positive results may occur. Experimentally, IHC can be employed to investigate the earliest changes in transformed tissues, identifying cellular changes not normally visible with H&E. Individual markers for proliferation, apoptosis, and specific tumor proteins can be used to help distinguish hyperplasia from neoplasia and determine specific tumor origin/type. IHC provides a relatively rapid and simple method to better determine the origin of neoplastic tissue or investigate the behavior or progression of a given neoplasm. Several experimental and diagnostic examples will be presented to illustrate the utility of IHC as a supplement to standard staining techniques.

Nitrogen cycling in coastal marine ecosystems.

It is generally considered that nitrogen availability is one of the major factors regulating primary production in temperate coastal marine environments. Coastal regions often receive large anthropogenic inputs of nitrogen that cause eutrophication. The impact of these nitrogen additions has a profound effect in estuaries and coastal lagoons where water exchange is limited. Such increased nutrient loading promotes the growth of phytoplankton and fast growing pelagic macroalgae while rooted plants (sea-grasses) and benthic are suppressed due to reduced light availability. This shift from benthic to pelagic primary production introduces large diurnal variations in oxygen concentrations in the water column. In addition oxygen consumption in the surface sediments increases due to the deposition of readily degradable biomass. In this review the physico-chemical and biological factors regulating nitrogen cycling in coastal marine ecosystems are considered in relation to developing effective management programmes to rehabilitate seagrass communities in lagoons currently dominated by pelagic macroalgae and/or cyanobacteria.

Absence of toxic effects in F344/N rats and B6C3F1 mice following subchronic administration of chromium picolinate monohydrate.

Chromium picolinate monohydrate (CPM) is a synthetic compound heavily marketed to consumers in the United States for use as a dietary supplement for muscle building and weight loss. The National Toxicology Program (NTP) tested the toxicity of this compound based on the potential for widespread consumer exposure and lack of information about its toxicity. Groups of 10 male and 10 female F344/N rats and B6C3F(1) mice were exposed to 0, 80, 240, 2000, 10,000, or 50,000 ppm CPM in feed for 13 weeks. CPM administration produced no effect on body weight gain or survival of rats or mice. Organ weights and organ/body weight ratios in exposed animals were generally unaffected by CPM. No compound-related changes in hematology and clinical chemistry parameters were observed. There were no histopathological lesions attributed to CPM in rats or mice.

A perspective on the biotechnological potential of extremophiles.

It is well recognized that many environments considered by man to be extreme are colonized by microorganisms which are specifically adapted to these ecological niches. A diverse range of bacteria, cyanobacteria, algae and yeasts have been isolated from such habitats and it is now widely accepted that these microorganisms provide a valuable resource not only for exploitation in novel biotechnological processes but also as models for investigating how biomolecules are stabilized when subjected to extreme conditions. This short review summarizes our current state of knowledge of this unique group of microorganisms and their enzymes, and attempts to identify their future biotechnological potential.

Sequential analysis of the pathogenesis of plutonium-induced pulmonary neoplasms in the rat: morphology, morphometry, and cytokinetics.

Light microscopy, morphometry, and cytokinetic techniques were used to examine the dynamics of plutonium-induced pulmonary proliferative lesions and neoplasms in rats at several intervals to 450 days after inhalation exposure to aerosols of 239PuO2. Maximal increases in alveolar and bronchiolar epithelial cell labeling were seen at 30 days; decreasing subsequently, the levels remained elevated above control indices. Focal proliferative epithelial lesions developed in the lung by 180 days and before the onset of pulmonary neoplasms. Pulmonary neoplasms, predominantly adenocarcinomas and squamous cell carcinomas, were initially observed at 308 days. The proliferative lesions progressed through a succession of morphological changes leading to the development of neoplasms. The volume density (fraction) and epithelial surface area of foci of alveolar epithelial hyperplasia increased progressively between 180 and 450 days after exposure, in contrast to the other proliferative lesions. We conclude that plutonium-induced pulmonary neoplasms develop through a succession of focal proliferative lesions that represent developmental preneoplastic lesions. Progressive increases in volume and epithelial surface area of the alveolar epithelial hyperplasias suggest that they may be more at risk for neoplastic transformation than the other histological types of proliferative foci.

Osmotically induced intracellular trehalose, but not glycine betaine accumulation promotes desiccation tolerance in Escherichia coli.

Trehalose considerably increased the tolerance of Escherichia coli to air drying, whether added as an excipient prior to drying or accumulated as a compatible solute in response to osmotic stress. The protective effect of exogenously added trehalose was concentration dependent, up to a threshold value of 350 mM. However, trehalose alone cannot explain the intrinsically greater desiccation tolerance of stationary compared to exponential phase E. coli cells, although their tolerance was also enhanced by exogenous or endogenously accumulated trehalose. In contrast, glycine betaine whether added as an excipient or accumulated intracellularly had no influence on desiccation tolerance. These data demonstrate that the protection provided by compatible solutes to cells subjected to desiccation differs from that during osmotic stress, due to the much greater reduction in available cell water. The protective effects of trehalose during desiccation appear to be due to its stabilising influence on membrane structure, its chemically inert nature and the propensity of trehalose solutions to form glasses upon drying, properties which are not shared by glycine betaine.

Toxicity and carcinogenicity studies of oxazepam in the Fischer 344 rat.

Oxazepam and related benzodiazepines are used in the treatment of anxiety. Carcinogenicity studies of oxazepam were performed with the F344 rat because of marked differences in tumor responses observed in NTP studies with B6C3F1 and Swiss-Webster mice compared to the results of Sprague-Dawley rat studies submitted to the FDA by a manufacturer to support registration of the drug. Groups of 50 male and 50 female F344/N rats were fed diets containing 0, 625, 2500, or 5000 ppm oxazepam for up to 105 weeks. A stop-exposure group of 50 males and 50 females received 10,000 ppm oxazepam in diet for 26 weeks, after which animals received control diet. All 5000- and 10, 000-ppm stop-exposure males died before the end of the study. Survival of 2500-ppm males and females was lower than that of controls. Body weight gains of 2500- and 5000-ppm males and females were less than those of controls. Male rats exposed to 2500 ppm had an increased incidence of renal tubule adenoma and hyperplasia. In addition, the incidences of renal tubule adenoma and hyperplasia were increased in the 10,000-ppm stop-exposure group. The incidences of nephropathy in exposed females were greater than those in controls, and the severity of nephropathy increased in exposed males. Epithelial hyperplasia and chronic inflammation of the nonglandular stomach were increased in males given 2500 and 5000 ppm and the incidence of ulcers of the nonglandular stomach in 2500-ppm males was also greater than that in controls. In males exposed to 5000 ppm, mineralization of the glandular stomach and erosion of the duodenum were observed. In females exposed to 2500 ppm, the incidences of epithelial hyperplasia, chronic inflammation, and ulcers of the nonglandular stomach and the incidence of erosion in the glandular stomach were increased. The incidences of centrilobular hepatocyte hypertrophy in males and females given 2500 and 5000 ppm were greater than those in controls. In summary, there was equivocal evidence of carcinogenicity in males based on increased renal tubule adenomas in groups which also had significantly enhanced nephropathy. There was no evidence of carcinogenicity of oxazepam in females given a diet containing 625, 2500, or 5000 ppm for 2 years or 10,000 ppm for 6 months.

Lung tumor induction by inhalation exposure to molybdenum trioxide in rats and mice.

Inhalation studies of molybdenum trioxide (MoO3) were conducted because of its wide use in industry, human exposure, and lack of data on carcinogenicity. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to MoO3 by inhalation at 0, 10, 30, or 100 mg/m3, 6 h/day, 5 days/week, for 2 years. In both rats and mice, survival and mean body weights of exposed groups of males and females were similar to those of their respective controls. There were significant exposure-dependent increases in blood molybdenum concentration in exposed rats and mice. There were no toxicological differences in bone density or curvature between exposed animals and their respective controls. In rats, dose-dependent increases in incidence of hyaline degeneration in the nasal olfactory epithelium and squamous metaplasia of the epithelium lining the base of the epiglottis were observed. The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) was marginally increased in males but not in females compared with controls. In mice, the incidences of squamous metaplasia of the epithelium lining the base of the epiglottis, hyperplasia of the laryngeal epithelium, and metaplasia of the alveolar epithelium were significantly increased in all exposed males and females compared with controls. The incidence of alveolar/bronchiolar adenoma or carcinoma (combined) in exposed groups of males and females was significantly greater than that in the control groups.

Toxicology and carcinogenesis studies of p,p'-dichlorodiphenyl sulfone in rats and mice.

p,p'-Dichlorodiphenyl sulfone (DDS) is used as a starting material in the production of polysulfones and polyethersufones, a family of thermoplastics. DDS was studied because of its high production volume and use. In toxicology studies, 10 Fischer 344 rats and 10 B6C3F1 mice/sex/group were fed diets containing 0, 30, 100, 300, 1,000 or 3,000 ppm DDS for 14 weeks. All animals survived until the end of the studies. Mean body weights of groups exposed to 300 ppm or greater were significantly decreased. Liver and kidney in rats and liver in mice were the major target organs of DDS toxicity. Dose-related increases in liver weights and incidences of centrilobular hepatocyte hypertrophy were observed in DDS-exposed groups. Nephropathy was seen in male and female rats only at and above 300 ppm. Neurotoxicity evaluations were negative in DDS-treated animals. Clinical chemistry and hematology parameters were minimally affected. In the 2-year toxicity and carcinogenicity studies, 50 rats and 50 mice/sex/group were fed diets containing 0, 10 (male rats), 30, 100, or 300 ppm DDS for 104 to 105 weeks. Survival of exposed groups was not affected. There were no clinical signs of toxicity related to DDS exposure. Final mean body weights were 2-17% lower in DDS-treated groups. Liver was the only target organ of DDS-induced toxicity. The incidence of centrilobular hepatocyte hypertrophy in mice and rats, and the incidence of bile duct hyperplasia and centrilobular degeneration in female rats was significantly greater than in controls. A no-observed-adverse-effect level (NOAEL) of 30 ppm DDS in the diet (1.5 mg/kg body weight) was established for rats. DDS was not carcinogenic in these studies.

Carcinogenesis studies of tetrahydrofuran vapors in rats and mice.

Tetrahydrofuran (THF) is a widely used industrial solvent and was selected for carcinogenesis studies by the National Toxicology Program (NTP) because of its potential for widespread occupational exposure in humans and a lack of information on animal toxicity and carcinogenicity. Groups of 50 male and 50 female F344/N rats and B6C3F1 mice were exposed to 0, 200, 600, or 1800 ppm THF by inhalation, 6 h per day, 5 days per week, for 105 weeks. Survival and mean body weights of male and female rats exposed to THF were comparable to that of the controls. No clinical findings or nonneoplastic lesions related to THF exposure were observed in male or female rats. The incidences of renal tubule epithelial adenoma or carcinoma (combined) in exposed male rats occurred with a positive trend, and in males exposed to 600 and 1800 ppm exceeded the historical range for controls in 2-year NTP inhalation studies. There were no other neoplastic lesions related to THF exposure observed in male or female rats. After week 36, the survival of male mice exposed to 1800 ppm was significantly lower than that of the controls. Mean body weights of male and female mice exposed to THF were similar to those of the controls throughout the study. Male mice exposed to 1800 ppm were observed in a state of narcosis during and up to 1 h after the exposure periods. Nonneoplastic lesions related to THF exposure were not observed in male or female mice. The neoplastic lesions related to THF exposure were seen in female mice only. In female mice exposed to 1800 ppm, the incidences of hepatocellular neoplasms were significantly greater than those in the controls. In conclusion, there was some evidence of carcinogenic activity of THF in male F344/N rats due to increased incidences of adenoma or carcinoma (combined) of the kidney at the 600 and 1800 ppm exposure levels. There was clear evidence of carcinogenic activity in female B6C3F1 mice based on increased incidences of hepatocellular neoplasms at the 1800 ppm exposure level. THF was not carcinogenic in female rats or male mice exposed at 200, 600, or 1800 ppm.

Long-term toxicity studies of ozone in F344/N rats and B6C3F1 mice.

The toxicity and carcinogenicity of ozone was evaluated in Fischer 344/N rats and B6C3F1 mice exposed to 0, 0.12 (2 years only), 0.5 or 1.0 ppm ozone by inhalation for 2-year and lifetime exposures. A 2-year cocarcinogenicity study (male rats only) included the subcutaneous administration of 0, 0.1 or 1.0 mg/kg/body wt. of 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) for the first 20 weeks along with inhalation exposure to 0 or 0.5 ppm ozone followed by additional 84 weeks of ozone exposure alone. Ozone exposure in rats did not cause an increased incidence of lung neoplasms. In the cocarcinogenicity study, ozone exposure did not have an additive carcinogenic effect. Lifetime and 2-year ozone exposure was associated with a marginal increase in lung tumors in male B6C3F1 mice and a more pronounced increase in females. Unique mutations in the K-ras gene were found in the mouse lung neoplasms from the ozone-exposed mice.

Bacterial interactions in the rhizosphere of seagrass communities in shallow coastal lagoons.

Rooted phanerogam communities in the shallow intertidal and subtidal coastal zone represent productive and healthy ecosystems. Inorganic nutrients are assimilated into seagrass biomass. Much of the organic matter resulting from moribund seagrass is rapidly mineralized, principally by bacteria. The microbial community of the rhizosphere is also highly active due to the supply of organic matter released during photosynthesis. This active sediment community plays an important role through carbon, nitrogen and phosphorous cycling in maintaining the stability and productivity of seagrass meadows. Over the last two decades, however, seagrass meadows in European coastal areas have declined due to increasing pollution. As eutrophication advances a trasition occurs from rooted phanerogram dominated communities to planktonic algal blooms and/or cyanobacterial blooms. Such changes represent the decline of a stable, high biodiversity habitat to an unstable one dominated by a few species. These changes of community structure can occur rapidly once the internal nutrient and organic matter control cycles are exceeded. A field investigation was undertaken to establish the spatial distribution of bacterial populations of Zostera noltii colonized and uncolonized sediment in the Bassin d'Arcachon, France. Bacteria were enumerated using both plate count and MPN techniques for different functional groups as well as determining the total bacterial populations present. Nitrogen fixation, ammonification, sulphate reduction rates, as well as alkaline phosphatase activity were also determined. Colonization of the Z. noltii roots and rhizomes was studied by light and scanning electron microscopy. Results confirmed that higher bacterial populations were present in the rhizosphere of Z. noltii compared to uncolonized sediments. Furthermore, electron microscopy identified the rhizome as the main site of colonization for a diverse range of morphological groups of bacteria. Sulphate reducing bacteria were identified as the key group of bacteria involved in N-fixation in the rhizosphere of Z. noltii. The data will be discussed in relation to the role played by the rhizosphere microflora in supplying and mobilising nutrients in Z. noltii.

14-Week toxicity and cell proliferation of methyleugenol administered by gavage to F344 rats and B6C3F1 mice.

Methyleugenol, a food flavor and fragrance agent, was tested for toxicity in male and female F344/N rats and B6C3F1 mice. Groups of 10 males and 10 females per sex per species were administered 0, 10, 30, 100, 300 or 1000 mg methyleugenol/kg body weight in 0.5% aqueous methylcellulose by gavage, 5 days per week for 14 weeks. Additional groups of rats and mice of each sex were dosed similarly and used for hematology and clinical chemistry studies. Groups of 10 male and 10 female rats and mice received the vehicle by gavage on the same dosing schedule and served as vehicle controls. For serum gastrin, gastric pH and cell proliferation studies groups of 10 female rats were given 0, 37, 75 or 150 mg/kg, once daily 5 days per week for 30 or 90 days or 300 or 1000 mg/kg for 30 days; male mice were given 0, 9, 18.5, 37, 75, 150 or 300 mg/kg for 30 or 90 days. For the gastrin, pH and cell proliferation studies, groups of 10 female rats and 10 male mice were given the vehicle for 30 or 90 days and served as controls. Methyleugenol administration to rats induced erythrocyte microcytosis and thrombocytosis in male and female rats. It also caused an increase in serum alanine aminotransferase and sorbitol dehydrogenase activities and bile acid concentration, suggesting hepatocellular injury, cholestasis or altered hepatic function. Additionally, methyleugenol induced hypoproteinemia and hypoalbuminemia, evidenced by decreased total protein and albumin concentrations in both male and female rats, suggesting in inefficiency of dietary protein utilization due to methyleugenol-induced toxic effects on the liver and glandular stomach of rats and mice. The increase in gastrin and gastric pH of rats and mice given methyleugenol suggests that gastrin feedback was impaired and resulted in conditions not conducive to protein digestion. In rats, methyleugenol caused an increase in the incidences of hepatocyte cytologic alteration, cytomegaly, Kupffer cell pigmentation, mixed foci of cellular alteration and bile duct hyperplasia of the liver and atrophy and chronic inflammation of the mucosa of the glandular stomach. In mice, it caused an increase in the incidence of cytologic alteration, necrosis, bile duct hyperplasia and subacute inflammation of the liver and atrophy, degeneration, necrosis, edema, mitotic alteration, and cystic glands of the fundic region of the glandular stomach. The increased incidences of adrenal gland cortical hypertrophy and/or cytoplasmic alteration in the submandibular salivary glands, adrenal glands, testis and uterus of rats were considered secondary to the chemical-related effects observed in the liver and glandular stomach. Based on mortality, body weight gain, clinical chemistry and gross and microscopic evaluation of tissues of rats and mice, the no-observed-effect level (NOEL) of methyleugenol for both species was estimated at 10 mg/kg.

Hetero-azeotropic distillation: combining fungal dehydration and lipid extraction.

A low-cost single-stage laboratory process combining fungal dehydration and lipid extraction was compared with a traditional two-stage method employing freeze-drying and subsequent mechanical disruption in the presence of solvent. The ability of a number of organic solvents to form hetero-azeotropes with water was exploited. Chloroform, cyclohexane and hexane were assessed in their abilities to both dry and extract lipid from the oleaginous phycomycete Mortierella alpina (ATCC 32222). Drying rate and lipid extraction were maximised under conditions that prevented fungal agglomeration. The total processing time was limited by the rate of dehydration rather than by the rate of lipid extraction. In all cases azeotropic distillation facilitated a greater rate of dehydration than was possible with freeze-drying. A consequent reduction in overall processing time was observed. Uniquely, both the solvent used and the mode of mixing employed controlled the morphology of the aggregates formed during distillation. In combination with mild mixing chloroform discouraged agglomeration whereas cyclohexane and hexane promoted aggregation. Successful lipid extraction was dependent on the use of dry biomass rather than on the application of heat to effect distillation. Neither the application of heat nor the solvent employed had any significant effect on the lipid composition of the extracted oil.

Developing the continuum of dental education: including dental foundation trainers in the delivery of a community-based clinical teaching programme.

INTRODUCTION: Despite advances in evidence-based dental school educational programmes, the charge is sometimes made that dental students are 'no longer as good as they used to be'. Recent modifications have meant that dental education is now a 'life-long experience', of which dental school is the initial, albeit very important, component. Contemporary dental students will normally enter dental foundation (DF) training on completion of dental school. As such there may be value in including DF trainers in dental school teaching programmes. The aim of this paper is to report the experiences, feedback and opinions of these DF trainers following their first-hand experience of the community-based clinical teaching programme at Cardiff, and assess if their perspectives of contemporary dental student education changed following this. MATERIALS AND METHODS: DF trainers were invited to attend the community-based clinical teaching programme at Cardiff on an observer basis. Twenty-four DF trainers attended, following which evaluation questionnaires were completed. Information sought included opinions and attitudes to the teaching programme, the physical environment in which the teaching programme took place, knowledge and attitudes towards community-based clinical teaching and modifications that DF trainers would make to the teaching programme to further improve the knowledge, skills and attributes of dental school graduates for DF training. RESULTS: Responses were received from 20 DF trainers (response rate = 83%). All 20 respondents felt that the teaching provided within the community-based clinical teaching programme was appropriate, with one respondent noting that it was like 'a day in the life of a dental practice', 'where anything could present'. Sixteen respondents were satisfied with the scope and content of the community-based clinical teaching programme, with a small number recommending inclusion of teaching in relation to inlays/onlays (n = 2), simple orthodontics (n = 1) and splinting (n = 1). Eighteen respondents reported that they felt students were adequately prepared for entry into DF training. All 20 respondents reported that their visit to the community-based clinical teaching programme had improved their perception of contemporary dental school education with one respondent noting: 'I am certainly more confident about students graduating' and another noting: 'It has reassured me that there are final year dental students that appear very professional and competent'. CONCLUSIONS: This investigation has demonstrated there is much to be gained by inclusion of DF trainers in undergraduate dental student community-based clinical teaching programmes. In an era where tensions exist between dental school teaching and subsequent DF training and independent practice, inclusion of DF trainers can exert positive pressures on dental school programmes and on DF training to ensure that young and newly graduating dentists are best prepared to meet the needs of their patients.

A preliminary investigation of the effects of salinity on the bacterial flora of the Tay estuary.

Two features of the effects of salinity on the bacterial flora of the Tay estuary are considered. First the effect of salinity on the size and species composition of the resident microflora at various sites within the estuary. The second part is concerned with data obtained from laboratory experiments designed to study the effects of subjecting marine and freshwater bacteria, isolated from the Tay, to salt stress.

Asparagine and glutamine metabolism in Rhodopseudomonas acidophila.

Rhodopseudomonas acidophila strain 7050 achieved balance growth when provided with either asparagine or glutamine as nitrogen source. Under these growth conditions R. acidophila synthesized a mixed amidase which exhibited similar activity (223--422 nmol/min . mg protein) against either nitrogen source. Determination of the free intracellular amino acid pools show that deamidation of asparagine and glutamine resulted in elevated levels of both aspartate and glutamate. Cell-free extracts of R. acidophila showed significant aminotransferase activity, particularly glutamine-oxaloacetate aminotransferase (89.7--209.3 nmol/min . mg protein), glycine oxaloacetate aminotransferase (135--227 nmol/min . mg protein), alanine glyoxylate aminotransferase (66.3--163.2 nmol/min . mg protein) and serine-glyoxylate aminotransferase (57.1--68.4 nmol/min . mg protein). Short term labelling experiments using 14C-glyoxylate show that glycine plays an important role in amino nitrogen transfer in R. acidophila and that the enzymes for the metabolism of glyoxylate via glycine, serine and hydroxypyruvate were present in cell-free extracts. These data confirm that R. acidophila can satisfy all its' nitrogen requirements by transamination.

Fatty acid and phospholipid composition of five psychrotrophic Pseudomonas spp. grown at different temperatures.

The free fatty acid and phospholipid composition of 5 psychrotrophic marine Pseudomonas spp. have been determined in chemostat culture with glucose as the limiting substrate over the range 0--20 degrees C. The predominant fatty acid present in all the isolates was hexadecenoic acid (C 16:1) together with lesser quantities of octadecenoic acid (C 18:1) whilst none contained acids with chain lengths exceeding 18 carbon atoms. Decreasing the growth temperature from 20 degrees C to 0 degrees C resulted in little significant change in fatty acid composition. The principal phospholipid components of the five psychrotrophic pseudomonads have been identified as phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Decreasing the growth temperature did not elicit significant changes either in the total quantities of phospholipid synthesized or in the concentration of individual phospholipid components in any of the isolates. All the psychrotrophs showed maximum glucose uptake between 15 degrees C and 20 degrees C and the rate decreased rapidly as the temperature was decreased towards 0 degrees C.