摘要:

Bacterioplankton productivity measurements based on [methyl-3H]-thymidine (TdR) orL-[3,4,5-3H]leucine (L-leu) incorporation typically depend on cold trichloroacetic acid (TCA) precipitation to separate3H uptake from incorporation. An additional rinse with cold 80% ethanol (EtOH) removed an average of 22 (L-leu) and 32% (TdR) of3H "incorporated" by San Francisco Bay samples and decreased the between-duplicate difference by a factor of 3.5. Similar results were obtained with samples from Tomales Bay, Calif., and Palmer Station, Antarctica. Varying amounts of cold TCA insoluble radiolabel from six other substrates were removed by the EtOH rinse. Regression analysis showed relationships between the effect of the EtOH rinse and a group of environmental variables and derived parameters. The percentage of3H removed was generally independent of filter type; however, there were often large differences in the amount of3H retained by Millipore versus Nuclepore or Poretics filters. The results strongly suggest that an EtOH rinse or other organic extraction should be included in protocols to determine incorporation of radiolabeled substrates into macromolecules. Furthermore, sequestering low molecular weight substrates in some sort of lipid-bound pool may represent a general storage mechanism employed by bacterioplankton.Key words: bacterioplankton, production, San Francisco Bay, filtration, incorporation.

ISSN:0008-4166    

DOI:10.1139/m92-100

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The binding of mutagenic pyrolyzates to cell fractions from some gram-negative intestinal bacteria and to thermally treated bacterial cells was investigated. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) were effectively bound by several of the bacterial cells. The cell wall skeletons of all bacteria effectively bound Trp-P-1 and Trp-P-2. Their cytoplasmic fractions retained Trp-P-1 and Trp-P-2, but to a lesser extent than the cell wall skeletons. 2-Amino-3-methylimidazo [4,5-f]quinoline (IQ) was not found in their cytoplasmic fractions. These cell wall skeletons also bound 2-amino-6-methyldipyrido[1,2-a:3′2′-d] imidazole (Glu-P-1), 2-amino-5-phenylpyridine (Phe-P-1), IQ, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQX). The amount of each mutagen bound differed with the type of mutagen and the bacterial strain used. The outer membrane ofEscherichia coliIFO 14249 showed binding of about 123.7 μg/mg of Trp-P-2, and its cytoplasmic membrane bound 57.14 μg/mg. Trp-P-2 bound to the bacterial cells was extracted with ammonia (5%), methanol, and ethanol but not with water.Key words: cell wall skeletons, outer membrane, cytoplasmic membrane, binding of mutagenic pyrolyzates.

ISSN:0008-4166    

DOI:10.1139/m92-101

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The kinetics of growth and formation of biofilm byStaphylococcus aureuswere investigated under iron-limited conditions in the chemostat. The population of planktonic cells reached 5.5 × 109cells/mL 24 h after inoculation (D = 0.05 h−1) and remained constant throughout. The number of biofilm cells ofS.aureuscolonizing the silicone tubing increased exponentially from 6 × 104to 2.7 × 107cells/cm2(6 days later) and continued to increase at a reduced rate to 2.7 × 108cells/cm2on day 13. Planktonic cells ofS.aureuswere susceptible to tobramycin and cephalexin. The planktonic cells could be successfully eradicated with a combination of 5 μg tobramycin plus 100 μg cephalexin per millilitre. Exposure of young biofilm cells ofS.aureusto 5 μg tobramycin plus 100 μg cephalexin per millilitre resulted in a rapid loss of cell viability. The percentage of survival dropped to less than 0.0001% after exposure to these concentrations of antibiotics for 3 h. Old biofilm cells ofS.aureuswere found to be extremely resistant to these antibiotics. The cell viability was reduced to 0.09% after exposure to 10 μg tobramycin plus 100 μg cephalexin per millilitre. The results suggest that it is possible to eradicateS.aureusinfection at the early stage with tobramycin plus cephalexin. Any delay in implementing antibiotic therapy is likely to result in the failure of the treatment. It is important to note that the concentrations of antibiotics required for the eradication of young biofilm cells must be determined for the treatment of device-associated infections.Key words: chemostat, biofilm, tobramycin, cephalexin,Staphylococcus aureus.

ISSN:0008-4166    

DOI:10.1139/m92-102

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Very high gravity wheat mashes containing 20 or more grams of carbohydrates per 100 mL were fermented completely bySaccharomyces cerevisiae, even though these mashes contained low amounts of assimilable nitrogen. Supplementation of wheat mashes with various amino acids or with yeast extract, urea, or ammonium sulfate reduced the fermentation time. However, lysine or glycine added as single supplements, inhibited yeast growth and fermentation. With lysine, yeast growth was severely inhibited, and a loss of cell viability as high as 80% was seen. Partial or complete reversal of lysine-induced inhibition was achieved by the addition of a number of nitrogen sources. All nitrogen sources that relieved lysine-induced inhibition of yeast growth also promoted uptake of lysine and restored cell viability to the level observed in the control. They also increased the rate of fermentation. Experiments with minimal media showed that for lysine to be inhibitory to yeast growth, assimilable nitrogen in the medium must be in growth-limiting concentrations or totally absent. In the presence of excess nitrogen, lysine stimulated yeast growth and fermentation. Results indicate that supplementing wheat mash with other nitrogen sources increases the rate of fermentation not only by providing extra nitrogen but also by reducing or eliminating the inhibitory effect of lysine on yeast growth.Key words: very high gravity, lysine inhibition, fuel alcohol, free amino nitrogen.

ISSN:0008-4166    

DOI:10.1139/m92-103

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The bactericidal properties of peracetic acid, hydrogen peroxide, chlorine, and formaldehyde were comparedin vitrousing a rapid micromethod. A combination of peracetic acid and hydrogen peroxide was also tested to assess interactions. The activities of these agents, which are widely used as disinfectants, were evaluated against water isolates and culture collection strains. Peracetic acid and chlorine exhibited an excellent antimicrobial activity, with a relatively rapid destruction of 105bacteria/mL. The time-dependent bactericidal activities of hydrogen peroxide and formaldehyde were the lowest. The combination of peracetic acid and hydrogen peroxide, tested by a checkerboard micromethod, was found to be synergistic. The minimal bactericidal concentration was established in terms of time for a given mixture of peracetic acid and hydrogen peroxide. Determination of bactericidal concentrations showed that synergy was maintained with increasing contact time. Concentrations for minimal times of treatment by chemicals that provided interesting activitiesin vitrowere tested for disinfection of ultrafiltration membranes. The bactericidal activities of peroxygen compounds were confirmed and synergism was maintained in working conditions. Chlorine showed a loss of efficacy when used on membranes.Key words: peracetic acid, hydrogen peroxide, chlorine, formaldehyde, minimal bactericidal concentration, ultrafiltration membranes.

ISSN:0008-4166    

DOI:10.1139/m92-104

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This work addressed the impact that the rhizosphere has on the biodegradation of foreign organic compounds. This was examined with live plants grown in a sewage sludge amended agricultural soil and a woodlot soil. Microcosms were designed that contained soil, roots, and microbial biomass in a compartment that excluded most of the plant stem and all of the leaf biomass. Control microcosms contained soils without plants and had no plant-induced rhizosphere microbial communities. Microbial mineralization of14C-labelled organic compounds (anionic, cationic, and nonionic surfactants) was measured by quantifying cumulative production of14CO2over a 40- to 55-day period. Regardless of the treatment, the surfactants were mineralized without lag periods. The mineralization results were fitted to mineralization models by nonlinear regression techniques. A mixed-order (3/2 order) mineralization model best fit the data. This model is similar to a first-order rate model but contains additional parameters that describe growth events or the mineralization of14C that has been incorporated or bound by the microorganisms. Of the compounds tested, sodium stearate was mineralized to the greatest extent (65% conversion to14CO2) in the sludge-amended agricultural soil. A cationic surfactant, dodecyltrimethylammonium chloride, was mineralized to the least extent (8%) by the microbes associated with corn roots in the sludge-amended soil. Linear alcohol ethoxylate was mineralized at the highest initial rate (1.5 day−1) in the presence of a soybean-induced rhizosphere in the woodlot soil. Overall, the rhizosphere treatments significantly increased the initial rates of mineralization by a factor of 1.1–1.9. However, there was no significant difference between the rhizosphere treatments and the soil-alone controls in the asymptotic yields of14CO2. The results suggest that rhizosphere microbial communities enhanced the biodegradation of surfactants in soils in terms of their effects on the initial rates of mineralization. However, because the total amounts of14CO2production were the same as in the no-plant controls, the extents of biodegradation of xenobiotic compounds may be limited by other factors, such as chemical and (or) physical interactions between the soil and the chemicals.Key words: rhizosphere, biodegradation, surfactants, soils, kinetics.

ISSN:0008-4166    

DOI:10.1139/m92-105

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

As part of the simultaneous fermentation of both glucose and xylose to ethanol by a coculture process, compatibilities between xylose-fermenting yeasts and glucose-fermenting species were investigated. Among theSaccharomycesspecies tested, none inhibited growth of the xylose-fermenting yeasts. By contrast, many xylose-fermenting yeasts, among the 11 tested, exerted an inhibitory effect on growth of the selectedSaccharomycesspecies. Killer character was demonstrated in three strains ofPichia stipitis. Such strains, despite their high fermentative performances, cannot be used to fermentD-xylose in association with the selectedSaccharomycesspecies. From compatibility tests between xylose-fermenting yeasts andSaccharomycesspecies, pairs of microorganisms suitable for simultaneous xylose and glucose fermentations by coculture are proposed. Strains associated in the coculture process are distinguished by their resistance to mitochondrial inhibitors. The xylose-fermenting yeasts are able to grow on media containing erythromycin (1 g/L) or diuron (50 mg/L), whereas theSaccharomycesspecies are inhibited by these mitochondrial inhibitors.Key words: killer character, erythromycin resistance, diuron resistance,Pichia stipitis.

ISSN:0008-4166    

DOI:10.1139/m92-106

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The genomes ofMycoplasma flocculareandMycoplasma hyopneumoniae, two mycoplasmas of the porcine respiratory system, were studied. Based upon antigenic cross-reactivity and DNA–DNA hybridization, these species have given indication of a close genetic relationship. By using field-inversion gel electrophoresis and employing the restriction digest fragments obtained from the gels as the probes, physical maps of the genomes of the two species were constructed.Mycoplasma hyopneumoniaeis similar toM.floccularein having a single set of rRNA genes and the 5S-rRNA gene is separated from the 16S and 23S rRNA genes. Based upon the location of the rRNA genes on the physical maps in both species, the distance between the 5S and the 16S and 23S rRNA genes is at least 150 kbp. Thus, there is further evidence for the close relationship between these organisms.Key words:Mycoplasma, Mollicutes, physical maps, rRNA.

ISSN:0008-4166    

DOI:10.1139/m92-107

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

RK2::Mu plasmids and transposon Tn5-Mob were used to mobilize theLegionella pneumophilachromosome. Plate matings betweenL.pneumophiladonors that contained RK2::Mu plasmids and auxotrophic recipients yielded recombinants at fequencies ranging from 10−6to 10−7per recipient for the markers tested. The presence of a Mu insertion in the chromosome of donors that harbored RK2::Mu plasmids increased the frequency of chromosome transfer of certain selected markers as compared with strains that contained RK2::Mu alone. Cotransfer experiments with Mu-containing donors and a thymidine and tryptophan auxotroph failed to reveal any linkage between thethyandtrploci inL.pneumophila. A strain that contained a chromosomal Tn5-Mob insertion and helper plasmid pRK24.4 transferred chromosomal markers at frequencies of 10−7per recipient. These findings suggest that RK2::Mu plasmids and Tn5-Mob may be useful for genetic mapping experiments withL.pneumophila.Key words:Legionella pneumophila, chromosome transfer, Tn5-Mob, RK2::Mu.

ISSN:0008-4166    

DOI:10.1139/m92-108

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

We measured the surface tension of a three-phase (solid–solid–liquid) system consisting of the bacteriumLactobacillus helveticusin a culture medium containing an expanded polystyrene support, to determine the adherence capacity of the bacteria to the support. The surface tension of the expanded polystyrene and theL.helveticuscells was evaluated by measuring contact angles. The Wilhelmy's microslide method was used to measure the surface tension of the liquid phase. The values obtained showed that the adherence capacity of theL.helveticuscells to expanded polystyrene pellets was not facilitated under the experimental thermodynamic conditions. The pellet surfaces and adhering bacterial cells were examined with a scanning electron microscope. The pellets exhibited several grooves in which microbial cells preferentially accumulated.Key words:Lactobacillus helveticus, adherence, surface tension, expanded polystyrene. [Translated by the journal]

ISSN:0008-4166    

DOI:10.1139/m92-109

出版商:NRC Research Press    

年代:1992

数据来源: NRC