The populations, characterization and activity of suspended bacteria in the Welsh River Dee

In a 29 month study of bacterial populations at three sites on the Welsh River Dee, the aerobic heterotrophic bacteria increased from an average basal level of about 1.2 times 10⁴ colony-forming units (cfu)/ml near the source of the river, to 2 times 10⁵ cfu/ml in the lower reaches. The ratio, total bacterial cell count: viable count, decreased from 70 in the upland reaches to 10 in the lower parts of the river. There was no apparent seasonal variation in bacterial numbers but on occasions the bacterial populations in both upland and lowland reaches of the river increased simultaneously. Fluctuations in bacterial numbers over a 50-fold range were observed in this study. Bacterial isolates from both upland and lowland sites were predominated by two groupings of bacteria, the Pseudomonas—Agrobacterium—Alcaligenes group and the Flavobacterium—Cytophaga—Flexibacter group. Results suggested that the latter group may have been part of the autochthonous population. Seasonal variation in heterotrophic potential ( V _max) for acetate uptake was shown to occur over a 30-fold range in the lowland reaches of the River Dee. Peaks in activity at the lowland site occurred during the summer months, the range of V _max values for acetate ranged from 0.2 to 30 μg/1/h. Fluctuations in V _max values from the upland site were not seasonal but were instead linked to faecal pollution, V _max values from this site range from 0.04 to 3 μg/1/h.     

Effects of Diflubenzuron on the Development of Bombyx mori (Lepidoptera: Bombycidae)

ABSTRACT This study was conducted to determine the effects of diflubenzuron (DFB) on the growth and development of the silkworm, Bombyx mori (L.). The DFB treatment extended abnormally the larval duration and affected negatively on larval spinning of the 5th instar. All the larvae treated with high DFB concentration (2.5 × 10^-1 and 2.5x 10^-1μg/μl) lost their spinning capability and finally died, whereas 62% of larvae treated with low DFB concentration (2.5 × 10^-1μg/μl)) spinned cocoon. The larval weights depended sensitively on the DFB treatment period rather than on the DFB concentration. The DFB treatment decreased the larval maturity less than 6% without regard to the concentration and treatment period. All the larva, when treated with DFB before the 5th days of the 5th instar, were not matured.     

A TEN-YEAR RECORD OF ABOVEGROUND BIOMASS IN A KANSAS TALLGRASS PRAIRIE: EFFECTS OF FIRE AND TOPOGRAPHIC POSITION

Measurements of mid-season live and dead aboveground biomass are reported for a 10-yr period (1975–84) in a northeast Kansas tallgrass prairie. Study sites included shallow, rocky upland and deep, non-rocky lowland soils in annually burned (April) and unburned watersheds. Lowland sites had significantly greater live biomass than upland sites for both burned and unburned prairie for the 10-yr period. Moreover, live biomass was greater on burned than unburned lowland sites, but was not significantly increased by fire on the upland sites. Averaged across upland and lowland sites, mid-season live biomass was 422 g m^–2 on annually burned and 364 g m^–2 on unburned sites for the 10-yr period. Each site had its lowest live biomass value during the severe drought year of 1980 (range = 185–299 g m^–2). During the study period, live biomass was most strongly correlated with seasonal pan water evaporation (r = –0.45 to –0.82), whereas dead biomass was correlated with the previous yr's precipitation (r = 0.61 and 0.90 for upland and lowland sites, respectively). When aboveground biomass was sampled throughout the 1984 season and separated into several components, biomass of the graminoids was 40% lower, whereas that of forbs and woody plants was 200–300% greater in the unburned than in the annually burned site.     

Respiration of Colpoda cucullus During Active Life and Encystment

SYNOPSIS. During encystment of Colpoda cucullus (O. F. Müller) the respiratory rate decreases from about 11.3 × 10^-5μl. O₂/hr. (mean value for active form) to about 1.3 × 10^-5μl./hr. (mean for unstable cyst); the process takes about 24 hrs. At the same time the activity of the contractile vacuole is stopped, but there is no correlation in time between the two processes: when respiration is inhibited by 1/2–2/3 the vacuolar activity is hardly changed. The respiration of unstable cysts remains approximately constant at least for 4 weeks. Experiments with methylene blue suggest that inhibition of respiration at encystment may be due to inhibition of terminal oxidase.     

Effect of 2-chloroethylphosphonic acid on capsule formation and alkaloid content in Papaver somniferum

Application of different concentrations of ethephon (2-chloroethylphosphonic acid) to Papaver somniferum L. at the times of stem elongation, bud, and capsule formation produced different effects. Ethephon (10^-2 M ) retarded growth of the plant and inhibited capsule formation during stem elongation, significantly reduced capsule size during the flowering period, but did not alter capsule development during capsule formation. When applied during the period of stem elongation, ethephon (10^-3 M and 10^-4 M ) reduced capsule size; alkaloid accumulation was reduced by ethephon at a concentration of 10^-3 M , but slightly increased by 10^-4 M . Ethephon (10^-3 M and 10^-4 M ) did not alter capsule development or alkaloid content significantly when applied during bud formation, but stimulated capsule size and alkaloid content when applied during capsule formation. Pretreating the plants with Ag⁺ (silver nitrate) did not reverse the ethephon effect. The results suggest that capsule maturation and alkaloid accumulation in P. somniferum are modified by ethylene, which is produced as a result of exogenous ethephon treatment.     

A Simple Cranial Window Technique for Optical Monitoring of Cerebrocortical Microcirculation and NAD/NADH Redox State. Effect of Mitochondrial Electron Transport Inhibitors and Anoxic Anoxia

Abstract: Fluorescence of NADH and vascular volume of the brain cortex of chloralose-anesthetized cats were measured by surface fluororeflectometry. A cranial window and superfusion technique was elaborated for the topical inhibition of mitochondrial electron transport in the brain cortex by amytal (inhibits at site I) and cyanide (inhibits at site III). The changes in NAD/NADH redox state and CVV evoked by these electron transport inhibitors were compared with those elicited by anoxic anoxia. Amytal (10^-3-10^-1 M ) and cyanide (10^-5-10^-2 M ) resulted in a concentration-dependent and reversible increase in cortical NAD reduction and vascular volume, but the cerebrocortical vessels were almost completely dilatated long before maximum NAD reduction was reached. Cyanide at 10^-2 M increased cortical NAD reduction and vascular volume as much as anoxic anoxia. Amytal at 10^-1 M induced approximately half of the NAD reduction evoked by 10^-2 M cyanide or anoxic anoxia, but resulted in only slightly less vasodilatation than that following cyanide and anoxic anoxia. Since amytal inhibits mitochondrial electron transport at site I—and cyanide and anoxia at site III—but induces a comparable degree of vasodilatation, it is concluded that cytochrome oxidase cannot be the single molecular oxygen sensor in the brain cortex.     

Factors affecting the distribution of genetic variability in the guppy, Poecilia reticulata

Previous studies on Trinidadian guppies have shown an apparent association of genetic variability, expressed as mean heterozygosity (Ho) at allozyme loci, with river order: fish from lowland sites exhibit higher mean Ho than their upland counterparts. Detailed genetic and behavioural observations were undertaken in the present study by repeated sampling throughout two river courses to examine population heterogeneity. Results show that the predation regime mediated mating behaviour of upland and lowland populations in the wild is not as divergent as previous laboratory observations have suggested. Furthermore, genetic variation at the eight loci variable in Trinidadian populations (p₁₀₀=0·13–O·88, H₀=O·03–0·23) appears to bear little association with predation regime, but is related to sub-structuring of populations by habitat features and geographic isolation. We therefore conclude that the observed patterns of genetic variability arise primarily as a consequence of stochastic as opposed to deterministic factors.     

Riparian zones as havens for exotic plant species in the central grasslands

In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m²subplots (nested in four 1000 m² plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m² subplots and 32 1000 m² plots). At the 1 m² scale, mean foliar cover of native species was significantly greater (P<0.001) in riparian zones (36.3% ± 1.7%) compared to upland sites (28.7% ± 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% ± 3.8% versus 8.2% ± 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m² scale, mean exotic species richness was also significantly greater (P<0.05) in riparian zones (7.8 ± 1.0 species) compared to upland sites (4.8 ± 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t =1.7, P=0.09) and total foliar cover (t = 2.4, P=0.02). Likewise, 26% of the variance in exotic species cover (log₁₀ cover) was explained by positive relationships with soil % silt (t =2.3, P=0.03) and total plant species richness (t = 2.5, P=0.02). At landscape scales (four 1000 m² plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r=0.73, P<0.05) and cover (r=0.74, P<0.05). Exotic species cover (log₁₀ cover) was positively correlated with log₁₀% N in the soil (r=0.61, P=0.11) at landscape scales. On average, we found that 85% (±5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (±8%) were found in upland plots. We conclude that: (1) species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists.     

Use of conductance measurements to detect growth of Clostridium botulinum in a selective medium

Growth of Clostridium botulinum in a selective medium (SBM) was monitored using conductance measurements. The correlation of log ₁₀ counts of spores and vegetative cells with detection times was highly significant ( r = 0.96, 0.97; P < 0.001). Log₁₀ counts of Cl. botulinum growing in pasteurized pork slurries also showed a clear linear relationship with detection times ( r = 0.77) but the confidence limits (± log₁₀ 2.3) of the regression line were too wide to estimate numbers of Cl. botulinum. For growth studies of Cl. botulinum in pork slurries detection times were useful in determining whether or not a visually unspoiled sample contained growing cells. Knowledge that a sample contained growing cells allowed a count to be made within 24 h, whereas 48 h would elapse before results from a traditional plate count were available.     

Modelling of the rate data from the fermentation of cassava slurry

Data from analyses of the fermentation of cassava slurry were used to derive kinetic constants for the rate of hydrolysis of bound cyanide, formation of free cyanide, pH change and fermentation. The pseudo-kinetic constant for the decay of bound cyanide was 1·6 times 10^-2/h and 2·5/h for free cyanide. Under the experimental conditions, the concentration of bound cyanide at any time during fermentation was 22·65e^-0·016tμg/g, where t is time in h. The fermentation rate constant was determined as 2·2871 times 10¹⁹. Based on the empirical expressions of the rate data, it is believed that rate constants of the intrinsic parameters of fermentation of systems similar to cassava slurry could be determined.     

Comparison of some decontamination methods and growth media for isolation of mycobacteria from northern brook waters

Two decontamination methods and five media were compared for the isolation of mycobacteria from brook waters of different physical, chemical and bacteriological characteristics. The decontaminants used were: 0.7 mol 1^-1 NaOH followed by 50 g 1^-1 oxalic acid and 0.9 mol 1^-1 H₂SO₄ combined with 0.5 g 1^-1 cycloheximide. The media compared were: Mycobacteria 7H11 agar with OADC enrichment (pH 6.6), glycerol egg (pH 6.5 and 5.5), and pyruvate egg (pH 6.5 and 5.5). All media contained cycloheximide, 0.5 g 1^-1. The NaOH—oxalic acid method generally resulted in lower contamination and higher isolation of mycobacteria than the H₂SO₄-cycloheximide method. With the NaOH—oxalic acid method, all five media were equal in positivity rates but contamination was a problem on Mycobacteria 7H11 agar. Of the four egg media tested, the highest positivity rate (92% of the samples) was obtained on the pyruvate modification (pH 6.5), and the highest mean colony count of mycobacteria (900 cfu 1^-1) on the glycerol modification (pH 6.5). Characteristics of water and sampling site had similar effects on the isolation frequencies of mycobacteria obtained by different combinations.     

Gorging response of Glossina palpalis palpalis to ATP analogues

ABSTRACT. The potencies of seventeen analogues of ATP as gorging inducers for Glossina palpalis palpalis were evaluated. The ranking for effective dose that induced half the flies to gorge (ED₅₀) was: A tetra P 5 ATP=2'd ATP ADP=2'd ADP > AMP-PNP > 3'd ATP 2'3'dd ATP > AMP-PCP > adenosine 5' triphosphate 2',3'dialdehyde AMP-CPP >> AMP. Females detect ATP and its analogues better than males. The ED₅₀ of ATP was 5 × 10^-7 M for teneral females and 1.5 × 10^-6 M for males. According to the potency order of the ATP analogues, the G.p.palpalis gustatory receptors recognizing ATP can be classified as P_2y purinoceptors.     

Ecology of Peridinium willei and P. volzii (Dinophyceae) in Danish lakes

The distribution of Peridinium willei and P. volzii was studied in Danish lakes. Both species were confined to lakes with concentrations of Total P < 0.15 mg 1^-1, with the majority of occurrences at Total P concentration between 0.020–0.040 mg 1^-1 and concentrations of PO₄ P between detection limit and 0.040 mg 1^-1. The occurrence of the species in relation to inorganic N compounds (NH₄ N and NO₂+ NO₃ N) was significantly broader for P. willei than for P. volzii: P. willei had an almost even distribution within a wide range of NH₄ N, whereas P. volzii mainly occurred between 0.001 and 0.10 NH₄ N 1^-1. P. willei had an almost even distribution at values beween 0.005 and 0.42 mg NO₂+ NO₃ N 1^-1, whereas P. volzii mainly occurred below 0.050 mg NO₂+ NO₃ N 1¹. P. willei was found at pH values between 4.2 and 8.5, whereas P. volzii was confined to lakes with a slightly basic pH. The study confirmed the broad limits of P. willei and the much more narrow limits of P. volzii in relation to seasonal occurrence and pH, as well as an affinity of the former to ponds and lakes with a rich bottom vegetation. The study also showed, however, that the species were not as widespread and common in recent Danish lake phytoplankton as generally stated by previous authors. The use of different ecological factors to give weight to species separation is discussed. The inclusion of P. volzii in P. willei proposed by Popovsky & Phiester is not supported by the present study, as the two taxa appear to have different ecological tolerances.     

Spontaneous All-or-Nothing Action Potentials in the Ciliate Bursaridium difficile

The electrical membrane properties and the swimming behaviour of the freshwater ciliate Bursaridium difficile were studied by current clamp recordings and video analysis. The resting membrane potential was –45 ± 6 mV (mean ± SD, n = 80), and the input resistance and membrane capacitance were 109 ± 42 megaohms (MΩ) (n = 63) and 457 ± 150 picofarads (pF) (n = 42), respectively. Based on an estimated surface area of 6.8 × 10^-4 cm², the corresponding specific membrane resistance and capacitance are 7.4 × 10⁴Ω× cm² and 0.7 μF/cm². Bursaridium difficile generates spontaneous, all-or-nothing action potentials with a well-defined threshold in normal medium. The spontaneous firing frequency was 0.22 ± 0.06 Hz (n = 80). The maximum rate of rise of the action potentials was less than 1 V/s, and they displayed a prolonged plateau phase (0.5–1 s). The action potentials were abolished in nominal Ca²⁺-free solution and are thus Ca²⁺-spikes. The swimming pattern of Bursaridium in homogeneous surroundings is composed of forward swimming periods interrupted by regular, short periods of backward swimming followed by a change in the forward swimming direction. The turning frequency corresponded to the spontaneous firing frequency, and only forward swimming was observed in nominal Ca²⁺-free solution. The periods of backward swimming activity are thus linked to the spontaneous action potentials.     

REGULATION OF OXYGEN CONSUMPTION IN NEUROBLASTOMA CELLS: EFFECTS OF DIFFERENTIATION AND OF POTASSIUM

Abstract— The rate of oxygen consumption has been measured micromanometrically in fresh mouse neuroblastoma cells and in corresponding cells cultivated with and without 20% calf serum known to suppress differentiation. Fresh cells and cells cultivated in the serum depleted medium showed a relatively intense respiration (0.5–1.0 × 10⁻⁵μl/h/cell), whereas the proliferating, cultivated cells had a low rate of oxygen uptake (0.2 × 10^-5μl/h/cell), provided they did not differentiate morphologically during the 4 h of measurement in the serum-free diver medium. Both morphological and metabolic differentiation of such cells occurs rapidly but may be completely prevented by siliconization of the divers.
An increase of the potassium concentration in the medium to 50 mM had essentially no effect on cultivated, differentiated cells, but led to an abolishment of oxygen uptake by fresh cells. No stimulatory effect of potassium was observed.     

EVALUATION OF ADENOSINE TRIPHOSPHATE (ATP) BIOLUMINESCENCE FOR ESTIMATING BACTERIA ON SURFACES OF BEEF CARCASSES

A rapid (<15 min), inexpensive and simple method has been developed to estimate the concentration of bacteria on surfaces of beef carcasses using adenosine triphosphate (ATP) bioluminescence. Surfaces (5x5 cm²) of beef carcasses (n= 159) were collected by excision. An ATP assay and aerobic plate count were performed on each sample. A significant (p < 0.001) positive linear relationship (r = 0.83) between plate count and ATP assay was obtained for 159 beef carcass samples. When thresholds levels were set at 1 × 10⁴, 1 × 10⁵ and 1 × 10⁶ CFU/cm², there was moderate to good agreement between the ATP bioluminescence assay and the aerobic plate count as determined by the k-statistic. The application of this ATP bioluminescence test to HACCP systems for beef slaughter processes is discussed.     

Nucleic acid contents and growth of first-feeding walleye pollock larvae in response to prey densities typical of sub-Arctic ecosystems

The growth, nucleic acid and protein contents of walleye pollock Theragra chalcogramma larvae reared at prey densities of 10, 30, 50, and 500 prey 1^-1 were measured for the first 9 days after the feeding initiation at 6° C. Incremental growth rates of larvae (mm day^-1) were low and variable for the first 7 days after feeding initiation. Growth rates and rates of RNA, DNA, and protein accumulation by larvae reared at 500 prey 1^-1 were positive while those of larvae reared at the lower prey levels did not differ significantly from zero. The RNA/DNA ratio was variable and exhibited no significant trend among food treatments. Estimates of instantaneous protein growth rates ranged from - 6·7 to 13·2% day^-1 at food densities of 10 and 500 prey 1^-1, respectively, and were moderately correlated with larval RNA/DNA ratios ( r = 0·628). The results suggest that in situ protein growth rates of first-feeding pollock larvae may be influenced by prey fields within the range of ambient food densities reported for sub-Arctic ecosystems.     

Resistance of a cased caddis larva to accidental entry into the drift: the contribution of active and passive elements

SUMMARY. . 1. The resistance to passive entry into the drift of first to fifth instar larvae of Allogamus auricollis (Pictet, 1834), a case-bearing caddis-fly, was investigated in the laboratory using an artifical stream channel.
2. Dead larvae in their cases were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to wash larvae away ranged from 3 cm s^-l (first instars) to 21 cm s^-1 for fifth instars. When the larvae were at right angles to the current (lateral position), these speeds were 2 and 9cm s^-1, respectively. In terms of force (Newtons), this passive resistance to drift ranged from 0.3x10^-6 N (first instar, frontal position) to 307.0x10^-6 N (fifth instar, frontal position). The data obtained in the experiments were in good agreement with values calculated from hydrodynamic equations, using biometric parameters of the larvae.
3. Total resistance to drift was studied by exposing living larvae to different current speeds. The speed just sufficient to wash larvae away ranged from 13 cm s^-1 in the first instar to 27.9 cm s^-1 in the fifth instar (frontal position). In terms of force, the total resistance to drift varied between 5.3x10^-6 N (first instar) and 547.5x10^-6 N (last instar).
4. The difference between total and passive resistance to drift was defined as'active resistance to drift', and is due to the effectiveness of a larva's attachment to the substrate. It ranged from 3.5x10^-6 N (first instar) to 222.8X 10^-6 N (last instar).     

The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/1 at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 times 10^-6 or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 times 10^-5–1 x 10^-4), and Pseudomonas spp. and Enterobacteriaceae (5 times 10^-3–1 x 10^-2 or greater). These organisms were killed rapidly when suspended in illuminated (170 μE/m²/s) solutions of Rose Bengal (1 times 10^-4 mol/1) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organisms were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 μE/m²/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 times 10^-5 mol/1) media exposed continuously to modest illumination (55–80 μE/m²/s).     

Evaluation of histidine decarboxylase activity of bacteria isolated from sardine (Sardina pilchardus) by an enzymic method

A fast and simple enzymic method has been adapted to measure histidine decarboxylase activity in bacteria isolated from fish. It was possible to quantify the presence of histamine at levels higher than 1.03 times 10^-2μmol (3 ppm) per ml of culture medium. There was a good correlation (γ=0.99) between the histamine content and the increase of absorbance in the concentration range of 3 and 30 ppm. The method can be used for quantitation of the amount of histamine produced by a selected strain, and has the advantages of being low in cost, reliable, easy to use and fast to perform. Plesiomonas shigelloides , a bacterium frequently isolated from fish and aquatic environments, has been identified as a new histamine-former in fish.