Canadian Journal of Microbiology
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Inhibition of the growth of grain-storage molds <i>in vitro</i> by the yeast <i>Pichia anomala</i> (Hansen) Kurtzman The potential use of yeasts to control grain-storage molds was evaluated by coculturing the yeast Pichia anomala with Penicillium roqueforti and Aspergillus candidus on agar plates, using different temperatures, water activities (aw ), and nutrient concentrations. Addition of 10 ppm cycloheximide to malt-extract agar inhibited Pichia anomala completely without affecting mold growth, making it possible to quantify the inhibition as a reduction in colony-forming units (cfu). For A. candidus, numbers of cfu and hyphal lengths were reduced at an initial yeast concentration of 104 cells/plate and reduced below detection limit at 108 cells/plate. A clear reduction in growth of Penicillium roqueforti was only observed at 108 yeast cells/plate. The antagonistic effect was generally more pronounced at low (6, 15 °C) and high (30, 37 °C) temperatures than at ambient ones. Pichia anomala inhibited growth of both molds more strongly in a substrate-rich medium than in a medium with a low substrate content. In water agar (low substrate concentration) the degree of inhibition of Penicillium roqueforti was larger at 0.96 aw than at 0.98 aw .Key words: biological control, Aspergillus candidus, Penicillium roqueforti.
Canadian Journal of Microbiology - Tập 39 Số 6 - Trang 623-628 - 1993
Decrease in soil microbial activity and biomasses owing to nitrogen amendments Microbial biomass and soil respiration rate decreased after application of 150 kg NH4 NO3 –N∙ha−1 to different coniferous forest podzols. The decrease was already found 3 months after fertilization and was still evident after 3–5 years. Changes in pH, organic matter, or water content in the soils could not explain the decreases. In laboratory experiments, several unfertilized forest soils were treated with 2 mg of NH4 NO3 –N or of urea–nitrogen∙g wet soil−1 . The ammonium nitrate addition resulted in severe depressions of the respiration rates during and up to 175 days of incubation and the decrease was evident after about 1 week. The urea treatment initially increased the respiration rate of the soils, but this appeared to be a transitory effect.
Canadian Journal of Microbiology - Tập 29 Số 11 - Trang 1500-1506 - 1983
Copper stress and filamentous fungus<i>Humicola lutea</i>103 — ultrastructural changes and activities of key metabolic enzymes Humicola lutea 103 is a copper-tolerant fungal strain able to grow in the presence of 300 μg·mL–1 Cu2+ under submerged cultivation. To prevent the consequences of copper overload, microorganisms have evolved molecular mechanisms that regulate its uptake, intracellular traffic, storage, and efflux. In spite of this avoidance strategy, high heavy-metal concentrations caused distinct and widespread ultrastructural alterations in H. lutea. The mitochondria were the first and main target of the toxic action. The effect of copper on activities of the key enzymes (hexokinase, glucose-6-phosphate dehydrogenase, malate dehydrogenase, and isocitrate dehydrogenase) included in the 3 main metabolic pathways, glycolysis, pentose phosphate pathway, and tricarboxylic acid cycle, was investigated. High metal concentrations exhibited a dramatic negative effect on hexokinase, while the other 3 enzymes showed a significant and dose-dependent stimulation. On the basis of the present and previous results we concluded that the copper-induced oxidative stress plays an important role in the fungal tolerance to high Cu2+ concentrations.
Canadian Journal of Microbiology - Tập 58 Số 12 - Trang 1335-1343 - 2012
Effect of hydrogen peroxide on antibacterial activities of Canadian honeys Honey is recognized as an efficacious topical antimicrobial agent in the treatment of burns and wounds. The antimicrobial activity in some honeys depends on the endogenous hydrogen peroxide content. This study was aimed to determine whether honey's hydrogen peroxide level could serve as a honey-specific, activity-associated biomarker that would allow predicting and assessing the therapeutic effects of honey. Using a broth microdilution assay, I analyzed antibacterial activities of 42 Canadian honeys against two bacterial strains: Escherichia coli (ATCC 14948) and Bacillus subtilis (ATCC 6633). The MIC90 and MIC50 were established from the dose-response relationship between antibacterial activities and honey concentrations. The impact of H2 O2 on antibacterial activity was determined (i) by measuring the levels of H2 O2 before and after its removal by catalase and (ii) by correlating the results with levels of antibacterial activities. Canadian honeys demonstrated moderate to high antibacterial activity against both bacterial species. Both MIC90 and MIC50 revealed that the honeys exhibited a selective growth inhibitory activity against E. coli, and this activity was strongly influenced by endogenous H2 O2 concentrations. Bacillus subtilis activity was marginally significantly correlated with H2 O2 content. The removal of H2 O2 by catalase reduced the honeys' antibacterial activity, but the enzyme was unable to completely decompose endogenous H2 O2 . The 25%-30% H2 O2 "leftover" was significantly correlated with the honeys' residual antibacterial activity against E. coli. These data indicate that all Canadian honeys exhibited antibacterial activity, with higher selectivity against E. coli than B. subtilis, and that these antibacterial activities were correlated with hydrogen peroxide production in honeys. Hydrogen peroxide levels in honey, therefore, is a strong predictor of the honey's antibacterial activity.Key words: honey, antibacterial activity, hydrogen peroxide, catalase, Escherichia coli, Bacillus subtilis.
Canadian Journal of Microbiology - Tập 52 Số 12 - Trang 1228-1237 - 2006
Effects of oxytetracycline, oxolinic acid, and flumequine on bacteria in an artificial marine fish farm sediment Oxytetracycline, oxolinic acid, and flumequine are at present the most frequently used antibacterial agents in the treatment of marine farmed fish in Norway. These substances are supplied with the food pellets and a substantial amount ends up in the sediment under the net pens. The effects of these antibacterial agents on the microbial community in a sediment were experimentally examined in tanks containing sediment to which was added either oxytetracycline, oxolinic acid, or flumequine, and supplied with a constant water flow. During the first 20 days of the experiment, approximately one-third of the antibacterial agents disappeared from the sediments. During the next 165 days another 25% vanished. There were elevated numbers of bacteria resistant to oxytetracycline and oxolinic acid a few days after the start of the experiment. The resistance that developed to oxytetracycline was higher and longer lasting than that to oxolinic acid and flumequine. Of the quinolones, flumequine seemed least disposed to induce resistance. The number of bacteria in all treated sediments decreased to 50–67% of the numbers in the control sediment 2 days after medication. Seven days after medication the sulfate reduction rates in the treated sediments were reduced to less than 10% of the rates found in the control. This effect lasted at least 29 days, but after 70 days the inhibition of the sulfate reduction in the treated sediments had disappeared. Key words: antibacterial agents, sediment, bacterial resistance, sulfate reduction.
Canadian Journal of Microbiology - Tập 38 Số 12 - Trang 1307-1312 - 1992
Enhancing plant productivity while suppressing biofilm growth in a windowfarm system using beneficial bacteria and ultraviolet irradiation Common problems in a windowfarm system (a vertical and indoor hydroponic system) are phytopathogen infections in plants and excessive buildup of biofilms. The objectives of this study were (i) to promote plant health by making plants more resistant to infection by using beneficial biosurfactant-producing Pseudomonas chlororaphis around the roots and (ii) to minimize biofilm buildup by ultraviolet (UV) irradiation of the water reservoir, thereby extending the lifespan of the whole system with minimal maintenance. Pseudomonas chlororaphis-treated lettuce grew significantly better than nontreated lettuce, as indicated by enhancement of color, mass, length, and number of leaves per head (p < 0.05). The death rate of the lettuce was reduced by ∼50% when the lettuce was treated with P. chlororaphis. UV irradiation reduced the bacteria (4 log reduction) and algae (4 log reduction) in the water reservoirs and water tubing systems. Introduction of P. chlororaphis into the system promoted plant growth and reduced damage caused by the plant pathogen Pythium ultimum. UV irradiation of the water reservoir reduced algal and biofilm growth and extended the lifespan of the system.
Canadian Journal of Microbiology - Tập 61 Số 7 - Trang 457-466 - 2015
Phylogenetic diversity of the <i>dddP</i> gene for dimethylsulfoniopropionate-dependent dimethyl sulfide synthesis in mangrove soils The dddP gene encodes an enzyme that cleaves dimethylsulfoniopropionate (DMSP) into dimethyl sulfide (DMS) plus acrylate and has been identified in various marine bacteria and some fungi. The diversity of dddP genes was investigated by culture-independent PCR-based analysis of metagenomic DNA extracted from 4 mangrove soils in Southern China. A phylogenetic tree of 144 cloned dddP sequences comprised 7 groups, 3 of which also included dddP genes from previously identified Ddd+ (DMSP-dependent DMS production) bacteria. However, most (69%) of the DddP sequences from the mangroves were in 4 other subgroups that did not include sequences from known bacteria, demonstrating a high level of diversity of this gene in these environments. Each clade contained clones from all of the sample sites, suggesting that different dddP types are widespread in mangroves of different geographical locations. Furthermore, it was found the dddP genotype distribution was remarkably influenced by the soil properties pH, available sulfur, salt, and total nitrogen.
Canadian Journal of Microbiology - Tập 58 Số 4 - Trang 523-530 - 2012
Selection of a stable clone of the MVPK-1 fetal porcine kidney cell for assays of foot-and-mouth disease virus The MVPK-1 cell line, derived from fetal porcine kidney cells, supports the replication of foot-and-mouth disease (FMD) virus. The cell line was adapted to grow in medium containing 5% bovine serum. The susceptibility of the adapted cells decreased as they aged at 37 °C. Various clones were isolated from the adapted cells and their growth characteristics and sustained susceptibility to FMD virus were compared. Clone 7 maintained uniform susceptibility to FMD virus over a 3-day period at 37 °C and proved superior to other clones in the characteristics studied. The clone has maintained satisfactory susceptibility to FMD virus through 40 subcultures. Clone 7 can replace primary bovine kidney cells for routine viral assays, but cannot detect as much FMD virus in animal specimens as primary bovine kidney, bovine thyroid, or swine kidney cells.
Canadian Journal of Microbiology - Tập 23 Số 3 - Trang 295-299 - 1977
THE INFLUENCE OF SOIL AND ROOT EXTRACTS ON THE ASSOCIATIVE GROWTH OF SELECTED SOIL BACTERIA These studies are concerned with the growth interrelationships of mixed cultures of five soil organisms in soil extract and root extracts of 2-, 4-, and 8-week-old oats, soybeans, and wheat. Population changes of Agrobacterium radiobacter, Arthrobacter citreus, Azotobacter chroococcum, Bacillus cereus, and a Pseudomonas sp. in pure and mixed culture were followed by plating on selective media. B. cereus and A. chroococcum grew poorly alone or in mixed culture in the extracts. In soil extract, A. citreus predominated over, or was nearly equal in number to, the Gram-negative forms (Pseudomonas and Agrobacterium). In root extracts, Pseudomonas sp. always predominated over A. citreus in mixed culture. A. radiobacter was inhibited in mature root extracts (8-week-old plants) although in pure culture it recovered after a period. An antagonistic effect of Pseudomonas sp. on A. chroococcum plated on nitrogen-free agar medium was found to be related to the kind of agar used.
Canadian Journal of Microbiology - Tập 9 Số 2 - Trang 187-197 - 1963
A review of issues related to measuring colonization of plant roots by bacteria Root colonization by introduced bacteria is an important step in the interaction of beneficial bacteria with the host plant. Investigators attempting to measure root colonization by bacteria must face several issues. A clear concept or definition of root colonization should be stated in each research summary, as several different definitions have been proposed. We consider true root colonists to be those bacteria that colonize roots in competitive conditions, i.e., natural field soils. Different methods of processing root samples are required if one is measuring external root colonization alone, internal colonization alone, or both. Given that most beneficial bacterial strains currently under investigation as root colonists are members of taxa naturally found in soils, a marking system is required to differentiate the introduced strain from members of the indigenous rhizosphere community. Spontaneous antibiotic resistance, immunological approaches, and foreign DNA sequences are among the marking systems that have been used and each has some possible advantages and disadvantages. More research is needed in the development and comparison of marking systems. The design of experiments to measure root colonization should take into account several statistical issues. One must decide what constitutes the sample unit for each replication of a given treatment, e.g., whole root systems or root segments. Consideration should also be given to how best to express the estimated population of root colonists (e.g., cfu/g fresh or dry weight root, cfu/cm root, or cfu/surface area root). Statistical analysis by standard analysis of variance tests should be used whenever possible to separate treatment means of colonization levels; however, one must determine that the underlying assumptions of these tests are correct for each experiment. Finally, in quantification of populations on roots, one will almost certainly encounter replications with no bacteria, i.e., zeros. There are several options for how to calculate treatment means when one or more replications is a zero, and the implications of these options are discussed. Key words: bioluminescence, genetic markers, plant growth-promoting rhizobacteria, rhizosphere bacteria, root, colonization.
Canadian Journal of Microbiology - Tập 38 Số 12 - Trang 1219-1232 - 1992
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