- Volume 137, Issue 9, 1991
Volume 137, Issue 9, 1991
- Physiology And Growth
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Topography of methanogenic subpopulations in a microbial consortium adapting to thermophilic conditions
More LessSummary: The microanatomy of a granular, methanogenic, microbial consortium (granule) was investigated by applying histochemical chemical techniques and light microscopy. The granules were obtained from a full-scale, mesophilic, upflow anaerobic-sludge blanket (UASB) bioreactor and were inoculated into laboratory-scale counterparts with a defined Substrate in which they were maintained for several weeks before shifting to thermophilic conditions. Samples for analysis were collected from the original inoculum, and from the laboratory-scale bioreactors before and after the temperature shift. Four months after this shift, the basic architectural plan of the granules was found to comprise a core or medulla, and a peripheral zone or cortex bounded by denser layers, and a spongy matrix formed by microbes and intercellular material. Also, five methanogenic subpopulations known to occur in these 4-month thermophilic granules were mapped to elucidate their spatial arrangement using immunofluorescence with antibody probes of predefined specificity spectra on histologic thin sections. Each subpopulation showed a distinctive distribution pattern; e.g. elongated surface and inner colonies for the methanogen antigenically related to Methanobacterium thermoautotrophicum ΔH, packets and cellular cords for the methanosarcina related to Methanosarcina thermophila TM1, bundles for Methanothrix rods, and dense or sparse lawns for the methanogens antigenically related to Methanobrevibacter arboriphilus AZ and Methanobrevibacter smithii ALI, respectively. These features were absent from, or much less developed in, the original inoculum granules, and before the temperature shift or even 1 week thereafter. All granules showed the same basic architecture involving a cortex and a medulla, but the inner texture of the mesophilic granules was considerably more compact than that of the 4-month thermophilic granules. Thus, the topography of methanogenic subpopulations and some structural details of the 4-month thermophilic granules Seem to be the result of adaptation to enrivonmental factors such as temperature, the same way as the array of methanogenic species and their numbers were found to be in previous work.
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Physiological regulation and optimization of lipase activity in Pseudomonas aeruginosa EF2
More LessSummary: Physiological regulation of extracellular lipase activity by a newly-isolated, thermotolerant strain of Pseudomonas aeruginosa (strain EF2) was investigated by growing the organism under various conditions in batch, fed-batch and continuous culture. Lipase activity, measured as the rate of olive oil (predominantly triolein) hydrolysis, was weakly induced by general carbon and/or energy limitation, strongly induced by a wide range of fatty acyl esters including triglycerides, Spans and Tweens, and repressed by long-chain fatty acids including oleic acid. The highest lipase activities were observed during the stationary phase of batch cultures grown on Tween 80, and with Tween 80-limited fed-batch and continuous cultures grown at low specific growth rates. The lipase activity of Tween 80-limited continuous cultures was optimized with respect to pH and temperature using response surface analysis; maximum activity occurred during growth at pH 6·5, 35·5 †C, at a dilution rate of 0·04 h−1. Under these conditions the culture exhibited a lipase activity of 39 LU (mg cells)−1and a specific rate of lipase production (q Lipase) of 1·56 LU (mg cells)−1h−1(1 LU equalled 1 μmol fatty acid released min−1). Esterase activity, measured with p-nitrophenyl acetate as substrate, varied approximately in parallel with lipase activity under all growth conditions, suggesting that a single enzyme may catalyse both activities.
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The use of acetate as an additional co-substrate improves methylotrophi growth of the acetogenic anaerobe Eubacterium limosum when CO2 fixation is rate-limiting
More LessSummary: Growth of the acetogenic anaerobe Eubacterium limosum on methanol/CO2 mixtures is limited by the rate at which CO2 can be assimilated. This limitation can be offset by the consumption of acetate as an additional co-substrate. Growth on methanol/CO2/acetate mixtures improves growth rates but stimulates production of an unidentified polymer leading to cell aggregation and wall growth under chemostat conditions. Production of butyrate as major fermentation end-product leads to growth inhibition visualized by an increased maintenance requirement as demonstrated by Y ATP estimations.
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The involvement of glutamate dehydrogenase and glutamine synthetase/glutamate synthase in ammonia assimilation by the basidiomycete fungus Stropharia semiglobata
More LessSummary: When grown on ammonia as sole nitrogen source, the basidiomycete fungus Stropharia semiglobata assimilated nitrogen via glutamate dehydrogenase (GDH). The two isoenzymes of GDH were both repressed by increasing concentrations of ammonia, but NADP-GDH (EC 1.4.1.4) was far more active than NAD-GDH (EC 1.4.1.2). Glutamine synthetase (GS; EC 6.3.1.2) and glutamate synthase (GOGAT; EC 1.4.7.1) were also active in S. semiglobata and these enzyme activities were independent of the ammonia concentration in the suspension. From enzyme activity and 1 5N-labelling studies of amino acids, it is concluded that both GDH and GS/GOGAT contribute to ammonia assimilation in this fungus.
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- Plant-Microbe Interactions
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Molecular genetics of Pseudomonas syringae pathovar pisi: plasmid involvement in cultivar-specific incompatibility
More LessSummary: A mutant (PF24) of the race 1 strain, 299A, of Pseudomonas syringae pv. pisi has been characterized in terms of its interactions with pea (Pisum sativum) cultivars. The mutant showed a changed reaction (avirulence to virulence) with a group of pea cultivars, including cvs. Belinda and Puget, previously thought to contain resistance genes R1 and R3. Avirulence towards cv. Puget was restored by transfer of any one of five cosmid clones from a race 3 (strain 870A) gene library to a rifampicin-resistant derivative of PF24. These observations were in agreement with a revised race-specific resistance genotype for Belinda and similar cultivars comprising a single resistance gene, R3. An incompatible interaction was observed between strain PF24 and cvs. Vinco (postulated to harbour race-specific resistance genes R1, R2, R3 and R5) and Hurst’s Greenshaft (R4 and possibly R1), indicating that the mutant retains at least one avirulence gene (A1 or A1 and A4). Mutant PF24 showed loss of a cryptic plasmid (pA V212) compared with its progenitor, strain 299A. A subclone (pAV233) of one of the race 3 restoration clones showed strong hybridization with similar-sized digestion fragments in race 3 plasmid DNA, confirming the A3 gene to be plasmid-borne. Strong cross-hybridization was also observed with a single 3·27 kb EcoRI fragment of plasmid DNA present in strain 299A but absent from strain PF24. This is consistent with the corresponding A3 determinant being located on pAV212 in the race 1 strain 299A. The novel avirulence gene corresponding to A3 in strain 870A is provisionally designated avrPpi3. A spontaneous race-change variant (strain 1759, which expressed no avirulence phenotype toward the pea differential cultivars) was derived from the race 3 strain 870A. This race 6 strain and a wild isolate of a race 6 strain both lacked plasmid DNA sequences corresponding to the insert in pA V233.
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Two different modes of attachment of Azospirillum brasilense Sp7 to wheat roots
More LessSummary: Two in vitro assays are described that can distinguish between two modes of attachment of Azospirillum brasilense Sp7 to wheat roots, and quantify the number of attached bacteria. The first assay measures A. brasilense adsorption (Ads), which reaches a maximal level within 2 h of incubation. Adsorption forces are weak, since adsorbed bacteria can be quantitatively removed by vortexing the root in water. In addition, adsorption is strongly reduced by pretreatment of A. brasilense cells with pronase E. The second assay measures A. brasilense anchoring (Anc), which begins only after 8 h of incubation and reaches a maximal level after 16 h. That adsorption and anchoring are different phenomena is further demonstrated by the properties of two classes ofA. brasilense attachment mutants. The first class of mutants, deficient in the production of a particular surface polysaccharide, has completely lost anchoring capability, but maintains wild-type adsorption capacity (Ads+Anc−). Mutants of the second class are defective in adsorption, but not in anchoring (Ads−Anc+). On the basis of these data, a two-step attachment mechanism of A. brasilense to wheat roots is proposed. The first step consists of a rapid and weak adsorption and depends on bacterial surface protein; the second step is, at least in vitro, independent of the first and consists of firm anchoring of adsorbed and free bacteria by means of bacterial extracellular polysaccharide.
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- Systematics
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An obligately anaerobic, coiled bacterium from Ace Lake, Antarctica
More LessSummary: A coiled or ‘C-shaped’, Gram-negative, non-motile bacterium was isolated from the anaerobic waters of Ace Lake, an Antarctic lake of salinity similar to seawater. The strain was obligately anaerobic and lacked oxidase, catalase and respiratory lipoquinones. It fermented glucose and peptones, and formed H2, CO2, and butyric, acetic and formic acids as major end-products. Pyruvate was metabolized to H2, CO2, and acetic and formic acids. The organism had an optimum temperature for growth of 15–16 °C, and no growth occurred at 22 °C. In synthetic medium, the generation time at 1·7 °C (in situ lake temperature) was 53 h. The optimum NaCl concentration for growth was 0·3 m, with poor growth at 0·1 m (5·8%, w/v). The mol% G + C of the DNA was 25·9 ± 0·4% (T m). The bacterium could not be accommodated within current bacterial species based on phenotypic criteria. Although coiled bacteria have been previously observed in Antarctic anaerobic environments, they had not been cultivated, and their metabolic capability and possible ecological role were unknown.
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Classification of acidophilic, neutrotolerant and neutrophilic streptomycetes by nucleotide sequencing of 5S ribosomal RNA
Summary: Complete 5S ribosomal RNA sequences were obtained for four acidophilic actinomycetes, seven neutrophilic streptomycetes and a strain of Streptoverticillium baldaccii. All of the organisms contained RNAs belonging to the 120 nucleotide type. An evolutionary tree was generated after combining the test data with results from similar studies on representative Gram-positive bacteria. The acidophilic, neutrotolerant and neutrophilic actinomycetes were recovered in a distinct cluster that was equated with the genus Streptomyces. The sequence data support the view that the genera Chainia, Elytrosporangium, Kitasatoa and Microellobosporia should be considered as synonyms of the genus Streptomyces. The recovery of the Streptoverticillium baldaccii strain on the fringe of the Streptomyces cluster is also consistent with current trends in the taxonomy of these organisms. Further work is needed to determine the taxonomic status of the two streptomycete subgroups that comprised the streptomycete cluster.
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- Corrigendum
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Volumes and issues
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