- Volume 137, Issue 6, 1991
Volume 137, Issue 6, 1991
- Physiology And Growth
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Metabolic response of Bacillus stearothermophilus chemostat cultures to a secondary oxygen limitation
More LessWith variously limited chemostat cultures of Bacillus s teawthermophilus, the glucose consumption rate increased markedly as the concentration of dissolved oxygen (d.o.t.; dissolved oxygen tension) was lowered from 50% to 1 % air saturation. Concomitantly, the specific rate of acetate production increased and lactate, which was not present in the fully aerobic cultures, accumulated in large amounts. Moreover, whereas at a high d.o.t. only an ammonia- limited culture excreted 2-oxoglutarate, all glucose-sufficient cultures excreted this metabolite at a d.o.t. of 1 % air saturation, even more being produced by a K+-limited culture than by the ammonia-limited one. The activities of those enzymes of glycolysis that were measured increased in parallel with the glucose consumption rate, as did the activities of enzymes of the Entner-Douderoff pathway. Similarly, the activities of lactate dehydrogenase and acetate kinase (which were synthesized constitutively also) reflected the corresponding metabolite production rates. Tricarboxylic acid (TCA) cycle activity markedly diminished with a lowering of the available oxygen supply and again (with the exception of aconitase and 2-oxoglutarate dehydrogenase) this was mirrored in decreases in the activities of TCA cycle enzymes. Assessments of energy flux in terms of ATP equivalents suggested that it was energetically more expensive to synthesize biomass at a low d.o.t. than at a high one. However, the presence of enzymes of the methylglyoxal bypass (methylglyoxal synthase and glyoxylase) at high activities in cells grown at a low d.o.t. render assessments of ATP flux rates unreliable.
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An efficient cyanide-degrading Bacillus pumilus strain
More LessSummary: A Gram-positive, aerobic, endospore-forming bacterium was isolated by an enrichment technique for the ability to degrade cyanide and was identified as a Bacillus pumilus strain. The bacterium rapidly degraded 100 mg I–1 of free cyanide in the absence of added inorganic and organic substances. The ability to degrade cyanide was linked to the growth phase and was not exhibited before late exponential/early stationary phase. Cyanide-degrading activity could not be induced before this time by the addition of 20 mg cyanide I–1. Production of the cyanide-degrading activity required 0·01 mg Mn2+ I–1 and did not occur at Mn2+ concentrations below 0·002 mg I–1. Cyanide-degrading activity was intracellular and cell-free extracts rapidly degraded cyanide.
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Comparison of growth characteristics of anaerobic fungi isolated from ruminant and non-ruminant herbivores during cultivation in a defined medium
Summary: Anaerobic fungi were isolated from rumen fluid of a domestic sheep (Ovis aries; a ruminant) and from faeces of five non-ruminants: African elephant (Loxodonta africana), black rhinoceros (Diceros bicornis), Indian rhinoceros (Rhinoceros unicornis), Indian elephant (Elephas maximus) and mara (Dolichotis patagonum). The anaerobic fungus isolated from the sheep was a Neocallimastix species and the isolates from non-ruminants were all species similar to Piromyces spp. A defined medium is described which supported growth of all the isolates, and was used to examine growth characteristics of the different strains. For each fungus the lipid phosphate content was determined after growth on cellobiose and the resulting values were used to estimate fungal biomass after growth on solid substrates. The ability of isolates from ruminants and non-ruminants to digest both wheat straw and cellulose was comparable. More than 90% and 60%, respectively, of filter paper cellulose and wheat straw were digested by most strains within 60–78 h. Growth of two fungi, isolated from rumen fluid of a sheep (Neocallimastix strain N1) and from faeces of an Indian rhinoceros (Piromyces strain R1), on cellobiose was studied in detail. Fungal growth yields on cellobiose were 64·1 g (mol substrate)–1 for N1 and 34·2 g mol–1 for R1. The major fermentation products of both strains were formate, lactate, acetate, ethanol and hydrogen.
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Influence of CO2 and low concentrations of O2 on fermentative metabolism of the rumen ciliate Dasytricha ruminantium
More LessSummary: The effects of ruminal concentrations of CO2 and O2 on glucose-stimulated and endogenous fermentation of the rumen isotrichid ciliate Dasytricha ruminantium were investigated. Principal metabolic products were lactic, butyric and acetic acids, H2 and CO2. Traces of propionic acid were also detected; formic acid present in the incubation supernatants was found to be a fermentation product of the bacteria closely associated with this rumen ciliate. 13C NMR spectroscopy revealed alanine as a minor product of glucose fermentation by D. ruminantium. Glucose uptake and metabolite formation rates were influenced by the headspace gas composition during the protozoal incubations. The uptake of exogenously supplied d-glucose was most rapid in the presence of O2 concentrations typical of those detected in situ (i.e. 1–3 μm). A typical ruminal gas composition (high CO2, low O2) led to increased butyrate and acetate formation compared to results obtained using O2-free N2. At a partial pressure of 66 kPa CO2 in N2, increased cytosolic flux to butyrate was observed. At low O2 concentrations (1–3 μm dissolved in the protozoal suspension) in the absence of CO2, increased acetate and CO2 formation were observed and D. ruminantium utilized lactate in the absence of extracellular glucose. The presence of both O2 and CO2 in the incubation headspaces resulted in partial inhibition of H2 production by D. ruminantium. Results suggest that at the O2 and CO2 concentrations that prevail in situ, the contribution made by D. ruminantium to the formation of ruminal volatile fatty acids is greater than previously reported, as earlier measurements were made under anaerobic conditions.
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Thermal inactivation of Listeria monocytogenes studied by differential scanning calorimetry
More LessSummary: The effect of NaCl on the thermal inactivation of Listeria monocytogenes has been investigated by conventional microbiological techniques and by using differential scanning calorimetry (DSC). Addition of 1·5 m-NaCI to cells grown at lower NaCl concentrations significantly increases the tolerance of cells to mild heat stress (56–62 °C). DSC thermograms show five main peaks which are shifted to higher temperatures in the presence of 1·5 m-NaCI. Measurement of loss of viability in the calorimeter gave good correlation between cell death and the first major thermogram peak at two NaCI concentrations. The time course of the loss of this first peak when cells were heated and held at 60 °C in the calorimeter matched the loss of viability, whereas the peak attributable to DNA showed little change during this process. The use of DSC to investigate the mechanisms involved in thermal inactivation is discussed.
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- Systematics
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Atypical characteristics of the salmonid pathogen Aeromonas salmonicida
D. McIntosh and B. AustinSummary: Incubation of Aeromonas salmonicida at supra-optimal temperatures, i.e. 30-37 °C, resulted in the expression of motility by polar flagella, and changes in sugar fermentation patterns, e.g. loss of acid production from mannitol, loss of the ability to degrade complex molecules (aesculin, DNA, elastin and gelatin), and an increase in antibiotic resistance (notably co-trimoxazole). Motility was enhanced in cultures grown in brain heart infusion broth supplemented with 18% (w/v) Ficoll.
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An integrated approach to the taxonomy of the genus Verticillium
More LessSummary: The taxonomic relationship among 64 isolates of the genus Verticillium was investigated using a range of morphological, physiological and biochemical characters with particular reference to V. lecanii. Forty-five isolates pertaining to the V. lecanii complex were compared, including isolates from arthropods (entomopathogens), rust fungi (hyperparasites) and ‘saprophytic’ sources. Other Verticillium species from invertebrate, fungal and plant hosts were included in the study to explore relationships within the genus. By analysing 41 characters, similarities were calculated between isolates using Gower's coefficient, and dendrograms were derived by average linkage clustering. Six cluster groups were delimited: V. lecanii isolates (7), mostly from homopteran insects; hyperparasitic isolates (3), including one of V. psalliotae, from rusts; V. lecanii isolates (18) mainly from insects of UK origin; V. lecanii isolates (7) from coffee rust; V. lecanii isolates (11) from scale insects, predominantly tropical; and two isolates of V. alboatrum. The remaining 16 isolates, mostly from Cordyceps and Torrubiella infections of tropical forest arthropods, did not fit into any cluster group and all probably represent undescribed anamorphs. A similar pattern was obtained when the electrophoretic properties of catalase isoenzymes were compared. Twelve catalase bands were identified. The taxonomic significance of these findings is discussed.
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Multivariate analyses of fatty acid data from whole-cell methanolysates of Prevotella, Bacteroides and Porphyromonas spp.
More LessSummary: The genus Bacteroides contains a number of biochemically and physiologically heterogeneous groups of organisms and needs taxonomic revision. In this study cellular fatty acids from a number of Bacteroides spp. were identified and quantified using gas chromatography and gas chromatography-mass spectrometry. The chemical data were then subjected to principal components analysis. In B. fragilis, which is the type species of the genus Bacteroides, C3-OH-iso17 was the predominant fatty acid (38.0%) and Cante15 was present in higher amounts (32.7%) than Ciso15 (14.6%). B.fragilis thus differed from all the other species examined: Prevotella (Bacteroides) buccae, P. (B.) oralis, P. (B.) oris, P. (B.) disiens, P. (B.) veroralis, P. (B.) heparinolytica and Porphyromonas (Bacteroides) endodontalis. Principal components analysis also enabled the closely related P. buccae, P. oralis and P. oris to be differentiated.
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