Use of antibiotic resistance mutations to track strains of obligately anaerobic bacteria introduced into the rumen of sheep

Selective plating procedures were used to follow the fate of rifampicin-resistant mutant strains of the obligately anaerobic species Bacteroides multiacidus and Selenomonas ruminantium after their introduction at numbers around 10⁷/ml into the rumen of sheep. Bacteroides multiacidus strain F100 showed an initially rapid rate of loss (49%/h) but subsequently numbers declined more gradually approaching the limits of detection (10³/ml) after 100 h. Viable cell numbers also decreased in vitro upon addition of F100 cells to whole rumen contents, but remained stable upon addition to cell-free rumen fluid, suggesting protozoal predation. F100 cells were able to grow in vitro in whole rumen contents in the presence of an added utilizable substrate such as sorbitol, but addition of sorbitol to the rumen failed to enhance survival in vivo . In the case of S. ruminantium , introduced rif^R strains persisted in the rumen at levels around 10⁶ ml for at least 30 days.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Survival of the recombinant Bacteroides thetaiotaomicron strain BTX in in vitro rumen incubations

The survival of Bacteroides thetaiotaomicron strain BTX under rumen-simulating conditions was studied. Strain BTX is a recombinant variant of strain 5482 engineered for the production of high levels of xylanase, an enzyme important in the degradation of hemicellulose. Strain BTX was not inhibited by compounds present in rumen fluid and it grew well in media containing rumen fluid (up to 75%) or high concentrations of volatile fatty acids (total concentration, 100 mmol l⁻¹). The ability of strain BTX to compete with other micro-organisms under rumen-like conditions was studied in in vitro incubations of rumen contents. These experiments employed a consecutive batch culture (CBC) system consisting of alfalfa suspended in a rumen fluid buffer inoculated with blended rumen contents and maintained by transfers (10%, v/v) at 48 h intervals. CBC cultures contained a diversity of microbial morphotypes and accumulated fermentation products in rumen-like proportions. When added alone, the numbers of BTX cells were maintained for only a few hours, and then declined precipitously until undetectable after 48 h. If CBC cultures were also supplemented with chondroitin sulphate (a mucopolysaccharide used by Bact. thetaiotaomicron ), strain BTX grew and the pattern of its population generally followed that of the total population of ruminal bacteria in these cultures. When transferred into fresh CBC cultures containing chondroitin sulphate, BTX was again able to grow and increase in numbers, but to a diminished degree. Although BTX was able to survive and maintain itself in chondroitin sulphate supplemented cultures, this was at a very low level (10¹⁰ ml⁻¹). The potential for manipulation of rumen function by inoculation with recombinant bacteria is discussed.     

Seasonal patterns in water, sodium and energy turnover in free-living echidnas, Tachyglossus aculeatus (Mammalia: Monotremata)

The energetics of an egg-laying mammal, the echidna ( Tachyglossus aculeatus ), were studied in the wild by means of isotope turnover techniques. Water and sodium influx rates were highest in summer (47.7±15.3 ml kg^-1 day^-1 and 1.20±0.52 mmol kg^-1 day^-1, respectively) and associated with high metabolic rates (0.509±0.048 ml CO₂ g^-1 h^-1). Water and sodium influxes and metabolic rates were lowest in May and June (7.8±6.4 ml H₂O kg^-1 day^-1, 0.21±0.12 mmol Na kg^-1 day^-1 and 0.205±0.129 ml CO₂ g^-1 h^-1, respectively). These low rates in late autumn/early winter are associated with reduced activity, the animals spending substantial periods of time in torpor. The comparatively low isotope turnover rates of echidnas are a consequence of their diet; ants and termites which have low mass-specific energy contents.     

Continuous ethanol production by flocculating yeast in the fluidized bed bioreactor

Abstract: Continuous fermentation by a highly flocculant strain of the yeast Saccharomyces cerevisiae was carried out in a tower fluidized-bed bioreactor. The synthetic and molasses media with a total sugar concentration of 17% (w/v) were used for fermentation. Different dilution rates were tested. Stable cell densities of 50 kg m^-3(dry weight) were maintained for all dilution rates. The ethanol productivity was increasing linearly with dilution rates up to 15—20 kg m^-3 h^-1. Aeration of the culture stabilized flocculating activity and viability of yeast and also permitted long-term operation of the bioreactor.     

Coupling of fermentation and microfiltration for α-amylase production from Bacillus amyloliquefaciens

Abstract: A strain of Bacillus amyloliquefaciens secreting α-amylase was cultivated continuously in a fermentor coupled to a filtration unit. Under the tested operating conditions, the maximum flux was 91 m^-2 h^-1 during the first day and 61 m^-2 h^-1 during the 2nd day. The α-amylase retention was around 30%. Compared to a batch process, continuous cultivation with cell recycling led to lower α-amylase concentrations but to a doubling of volumetric productivities.     

Effects of glyphosate on nitrogen fixation of free-living heterotrophic bacteria

The effect of the herbicide glyphosate ( N -(phosphonomethyl)glycine) on the growth, respiration and nitrogen fixation of Azotobacter chroococcum and A. vinelandii was studied. Azotobacter vinelandii was more sensitive to glyphosate toxicity than A. chroococcum. Recommended dosages of glyphosate did not affect growth rates. More than 4 kg ha^-1 is needed to find some inhibitory effect. Specific respiration rates were 19.17 mmol O₂ h^-1 g^-1 dry weight for A. chroococcum and 12.09 mmol h^-1 g^-1 for A. vinelandii. When 20 kg ha^-1 was used with A. vinelandii , respiration rates were inhibited 60%, the similar percentage inhibition A. chroococcum showed at 28 kg ha^-1. Nitrogen fixation dropped drastically 80% with 20 kg ha^-1 in A. vinelandii and 98% with 28 kg ha^-1 in A. chroococcum. Cell size as determined by electron microscopy decreased in the presence of glyphosate, probably because glyphosate induces amino acid depletion and reduces or stops protein synthesis.     

Dose responses of tsetse flies (Glossina) to carbon dioxide, acetone and octenol in the field

ABSTRACT Studies were conducted in Zimbabwe of the catch of Glossina pallidipes Austen from an electric net plus target baited with mixtures of acetone plus carbon dioxide or 1-octen-3-ol (octenol) plus carbon dioxide. For acetone dispensed alone at 5–50, 000 mg h^-1, ten-fold increments in the dose increased the catch 1.7 times. For carbon dioxide dispensed alone, dose increments from 12 to 1201 h^-1 doubled the catch, but the catch was not further increased by dispensing carbon dioxide at 600–1200 1 h^-1. For mixtures of these two odours, ten-fold increments in the dose of carbon dioxide between 12 and 12, 0001 h^-1 increased the catch c . 2.5 times if acetone was also dispensed at >50 mg h^-1; changes in the dose of acetone between 50 and 50 000 mg h^-1 did not affect the catch. The addition of octenol (0.05 mg h^-1) to carbon dioxide (12–12001 h^-1) doubled the catch. Ten-fold increments in the dose of octenol between 0.05 and 5 mg h^-1 did not increase the catch significantly and the catch was independent of changes in the dose of carbon dioxide between 120 and 12001 h^-1. The behavioural basis of the dose-response curves was investigated using an incomplete ring of electric nets to assess the flight orientation of tsetse in different odours. Upwind flight was not elicited by acetone or octenol alone, or by carbon dioxide unless it was at very high doses, however, mixtures of carbon dioxide with acetone or octenol elicited upwind flight. It is suggested that the attractiveness of mixtures of acetone and carbon dioxide is a function of the region of overlap of these two odours at above threshold concentration. Acetone and octenol on their own appear to increase the responsiveness of flies to visual cues.     

Nickel and rubidium uptake by whole oat plants in solution culture

Nickel and rubidium uptake by oat plants ( Avena sativa L. cv. Victory) were examined in relation to solution temperature, solution concentrations, metabolic inhibitors, anaerobic root conditions, transpiration and time. Over a 4-h period, uptake rates for both Ni²⁺ and Rb⁺ remained constant at 23°C. Decreasing temperatures to 2°C, 20 μ M concentrations of 2,4-dinitrophenol (DNP), or anaerobic root conditions decreased Ni²⁺ and Rb⁺ uptake rates by 97 to 86% in whole plants. Treatment of excised roots with 20 μ M DNP decreased Ni²⁺ uptake by 93%. Nickel and Rb⁺ uptake rates measured as a function of the external solution concentration followed a typical parabolic curve. K_m (0.012 m M ) and V_max [2.72 μmol (g dry weight)^-1 h^-1] values for Ni²⁺ were nearly 7 times lower than those for Rb⁺ [0.09 m M and 19.2 μmol (g dry weight)^-1 h^-1]. In all experiments, Ni²⁺ and Rb⁺ showed qualitatively similar uptake patterns, but Rb⁺ uptake was quantitatively more sensitive than Ni²⁺ to experimental manipulations.     

Effect of hunger on the daily pattern of feeding rates in juvenile pink salmon, Oncorhynchus gorbuscha Walbaum

Juvenile pink salmon, Oncorhynchus gorbuscha , in two test groups of differing hunger level fed continuously on live copepods, maintained at high densities, throughout 12 h feeding periods in the laboratory. Analysis of video films showed that mean feeding rates were initially (first 10 min) between 51.5 and 63.8 prey-capture attempts (snaps) fish^-1 10 min^-1, but declined abruptly with increasing satiation to relatively constant levels of about 5.0 and 8.0 snaps fish^-1 10 min^-1, which were maintained during the subsequent 11 h of feeding. The data suggests that after the initial filling of their stomachs with food, juvenile pink salmon keep their stomachs full by feeding at a rate that balances the gastric evacuation rate of 18.6 mg prey h^-1 at 11° C. Less than 15% of the fish's stomach contents need be evacuated apparently for spontaneous feeding to resume or occur. Increased hunger level (by increasing a pre-test food deprivation period from 24 to 72 h) resulted in fish increasing their average feeding rate and thus their ration consumed from 23.6 to 39.8% dry body weight per 12 h.     

Limitations of the enzyme-linked immunosorbent assay for routine determination of legume inoculant quality

Peat inoculants containing strains of either Rhizobium or Bradyrhizobium spp. were used to determine correlations between cell numbers and A₄₀₅ values obtained with double antibody sandwich enzyme-linked immunosorbent assay (DAS ELISA) and indirect ELISA. ELISA values of inoculants containing strains of Rhizobium were weak and non-specific; with Bradyrhizobium spp. strains, readings were higher and cross-reactions negligible when heated inoculant suspensions were allowed to stand for 3 h before ELISA determinations were made. With soybean inoculant, correlation coefficients of r = 0.93 and 0.83 were obtained with DAS and indirect ELISA, respectively. A linear curve relating log cell numbers to A₄₀₅ values was used to determine the reliability of DAS ELISA values obtained over 2 years with tests on commercially produced soybean inoculants. In the range 5 times 10⁸-ca 3 times 10⁹ cells/g inoculant, DAS ELISA estimates closely followed plate counts but no significant correlation was found when inoculants contained >ca 3 times 10⁹ cells/g. With a minimum requirement of 1 times 10⁹ cells/g inoculant, discrepancies between DAS ELISA estimates and plate counts obtained with inoculants produced with gamma-irradiated peat would have resulted in the erroneous rejection or acceptance of 14.5% of all inoculants tested, based on DAS ELISA estimates. With inoculants produced with steam-sterilized peat, which was unfavourable for survival of strain WB1, 70.0% of the inoculants rejected because of low plate counts would have been acceptable on the basis of DAS ELISA estimates.     

Growth of thermophilic obligately autotrophic hydrogen-oxidizing bacteria on thiosulfate

Thermophilic obligately autotrophic H₂-oxidizing bacteria from Icelandic hot springs were tested for growth on thiosulfate. Ten strains were tested and all grew on thiosulfate but not on sulfite or sulfur. The product of thiosulfate oxidation was sulfate. The growth rate on thiosulfate was slower (μ=0.12 h^-1) than on H₂ (μ=0.34 h^-1). Washed cells which had been grown on thiosulfate could oxidize thiosulfate rapidly but H₂-grown cells oxidized thiosulfate much more slowly and with about a 3 h lag time. The bacteria would not grow on agar medium under H₂ but grew on agar medium containing thiosulfate.     

Drinking rate, uptake of bacteria and microalgae in turbot larvae

The drinking rate of turbot larvae increased from 14 to 120 nl larva^-1 h^-1 from day 2 to 11 after hatching, which gave a slightly increased specific drinking rate (calculated per biomass) from day 2 to 7 (0·8–1·9 nl μg carbon^-1 h^-1. The clearance rate of both algae and bacteria was 10–100 times higher than the drinking rate, which indicated that the larvae had an active uptake of both algae and bacteria. On day 2 and 4 after hatching highest clearance rate was observed for Tetraselmis sp. On day 6 about the same clearance rate was observed for bacteria, Isochrysis galbana and Tetraselmis sp. Until day 4 the turbot larvae had a higher ingestion rate of Tetraselmis sp. than of I. galbana , whereas on day 6 the rates were similar (28–41 ng carbon larvae^-1 h^-1). The assimilation efficiency was somewhat higher for I. galbana than for Tetraselmis sp., and on day 6 the assimilated algae constituted 1·5 and 0·9% of the larval biomass for I. galbana and Tetraselmis sp., respectively.     

The influence of pH and growth rate on production of the bacteriocin, bavaricin MN, in batch and continuous fermentations

Bavaricin MN, a bacteriocin produced by Lactobacillus bavaricus MN, reached titres of 2000 AU ml^-1 in APT broth maintained at pH 6.0, 30°C in a batch fermenter. Levels of bavaricin MN at pH 5.5 and 6.5 were lower despite comparable levels of producer cells. The addition of 3.0 g l^-1 beef extract to APT broth resulted in increases in both the growth rate of the culture and the production of bavaracin MN. The titre of bavaricin MN in batch fermenters controlled at pH 6.0 in APT broth plus 3 g l^-1 beef extract reached 3200 AU ml^-1 at 30°C. This level was reduced to 800 AU ml^-1 by 76 h. Glucose-limited continuous culture of Lact. bavaricus MN under the same conditions resulted in an increase in the titre of bavaricin MN to 6400 AU ml^-1. This level was maintained, independent of growth rate, for 345 h. Growth rates of 0.205, 0.118, 0.169 and 0.058 h^-1 were examined.     

Photosynthesis and carbohydrate partitioning in sweet cherry: Fruiting effects

The effect of fruiting on carbon fixation and retention in leaves was monitored by measuring net photosynthesis (Pn) and total non-structural carbohydrates (TNC) on a seasonal basis on mature fruiting and non-fruiting sweet cherry trees ( Prunus avium L. cv. Bing). Pn was also measured diurnally during stages II and III of fruit development. Pn rates increased to between 18 and 20 mg CO₂ dm^-2 h^-1 during stage II of fruit development and were maintained until harvest. Diurnally, Pn increased in the morning to 20 mg CO₂ dm^-2 h^-1 and this rate continued until sunset. Leaf carbohydrate levels decreased in both fruiting and non-fruiting trees beginning at the equivalent of stage II of fruit growth. Carbohydrates were lower in leaves and woody portions of current, 1- and 2-year-old shoots of fruiting trees. Although differences were found in levels of non-structural carbohydrates, no differences in Pn were found in fruiting vs non-fruiting plants on either a seasonal or a diurnal basis. Pn rates in swet cherry in the field were primarily affected by ontogeny and environment and not by sink strength.     

INFLUENCE OF OXIDATION-REDUCTION REDUCTANTS ON SALMONELLA TYPHIMURIUM GROWTH RATES AFTER INITIAL pH ADJUSTMENT AND ZINC COMPOUND ADDITION

The objective of this study was to examine the separate influence of acidic pH, reductants (cysteine and sulfide) and zinc compounds (Zn acetate and Zn sulfate) during anaerobic growth of a S. typhimurium poultry isolate in rich or minimal media. The anaerobic growth of a S. typhimurium poultry isolate in TSB medium was significantly inhibited by either acidic initial pH or higher concentrations of Zn acetate. S. typhimurium anaerobic growth in M9 minimal medium was significantly inhibited by either acidic pH or higher concentrations of Zn acetate or Zn sulfate. Most anaerobic growth rates of the S. typhimurium poultry isolate in acidic media and with higher concentrations of Zn acetate or Zn sulfate were less than 0.10 h^-1. The overall anaerobic growth rates of S. typhimurium were inhibited more in the presence (0.089 h^-1) of reductants than in the absence (0.102 h^-1) of reductants in M9 medium. Results in this study suggest that either increasing Zn concentration or decreasing initial pH can reduce growth rate of foodborne Salmonella under anaerobic growth conditions.     

Comparison of conductimetric and traditional plating techniques for detecting yeasts in fruit juices

Frozen fruit juice concentrates containing an average microbial population of log₁₀ 1.54 cfu ml^-1 were examined by traditional plating techniques and direct and indirect conductimetry. The initial populations in diluted (1:4) concentrates increased to an average of log₁₀ 3.82 cfu ml^-1 during incubation at 25°C for 24 h. Incubation before plating and subjecting to conductimetric tests also facilitated the resuscitation of cells that may have been freeze-injured. Yeasts were recovered in equal numbers on acidified (pH 3.5) potato dextrose agar and dichloran rose bengal chloramphenicol agar (pH 5.6). Yeasts and bacteria were recovered on orange serum agar. Detection times determined by indirect conductimetry correlated fairly well ( r = -0.73) with populations (cfu ml^-1) detected on traditional plating media. Populations in diluted concentrates which were not incubated before examination were detected conductimetrically in an average of 48.9 h, whereas detection times for diluted concentrates incubated for 24 h at 25°C before testing were reduced to an average of 14.1 h. Examination by conventional (direct) conductimetry required an additional 10–20 h to reach changes in conductance of 5 μS h^-1.     

Pectinolytic enzymes of anaerobic fungi

Pectinolytic enzymes of four rumen fungi have been described. Three fungal species were monocentric Neocallimastix spp. H15, JL3 and OC2, and one isolate was a polycentric strain of Orpinomyces joyonii , A4. They differed in degree of pectin degradation and utilization. Only the strain Neocallimastix sp. H15 and partially Orpinomyces joyonii A4 were able to utilize pectin to a higher extent. The most important pectinolytic activity in all these isolates represented pectin lyase (EC 4.2.2.10) and polygalacturonase (EC 3.2.1.15). Their specific activities were in the range of 100–900 and 10–450 μg galacturonic acid h^-1 mg protein^-1 for pectin lyase and polygalacturonase, respectively. Polygalacturonase, located mainly in the endocellular fraction, was inhibited by calcium ions and had the main pH optimum at pH 6.0. All strains produced pectate lyase (EC 4.2.2.2). None of the strains tested produced pectinesterase (EC 3.1.1.11).     

Water vapour uptake by diapausing eggs of a tropical walking stick

Abstract. This study is the first to demonstrate the capacity of an arthropod egg, that of a tropical walking stick Extatosoma tiaratum (Macleuy), to absorb water vapour from the air. This species diapauses both as an early embryo and then again as a pharate first instar larva, and both stages are capable of absorbing water vapour. Water vapour absorption occurs at lower humidities and at a lower rate for an egg in early embryonic diapause (c. a_v 0.30, 0.516 mg h^-1δ_v^-1) than in the diapausing pharate first instar (c. a_v 0.60, 0.725 mgh^-1δa_v^-1) at 25C. In addition to having the capacity to gain water at very low vapour activities, water is efficiently conserved as indicated by the low rate of water loss (0.015% h^-1 in the early embryo and 0.046% h^-1 in the pharate larva at 25C). Eggs that have been killed lose water when held at a hydrating vapour activity, thus implying that active uptake contributes to net absorption. Wax block experiments suggest that water is absorbed over the entire chorionic surface. Eggs of five other insect species that were examined [Lymantria dispar (L.), Bombyx mori (L.), Antheraea polyphemus (Cram.), Oncopeltus fasciatus (Dallas) and Diaferomera femorata (Say)] lacked the ability to absorb atmospheric water.     

Oxygen consumption of East Siberian cod: no support for the metabolic cold adaptation theory

Standard metabolic rate ( R _s) at 2°C of eight East Siberian cod Arctogadus borisovi , caught in West Greenland, body mass of 601.5 ± 147.6 g (mean ± s.D.), was 40.9 ± 5.9 mg O₂ kg^-1 h^-1 and 59.0 ± 6.6mg O₂ kg^-1 h^-1 when extrapolated to a standardized 100 g fish. R _s was compared with three other Gadidae, to test the theory of metabolic cold adaptation (MCA). There was no evidence of MCA in the family.