摘要:

The response of attached bacteria to Zn at three pH levels was studied in outdoor stream mesocosms. Streams containing water from Crooked Lake, Indiana, were dosed with either 0.1 or 0.5 mg Zn/L at ambient pH (pH 8.4), pH 7.0, or pH 5.5. Samples were taken at 2, 5, 10, and 20 days and analyzed for total biomass, chlorophyll content, total bacterial numbers, and heterotrophic activity. All measures of community abundance and activity were highest in the treatment receiving 0.1 mg/L at a pH of 8.4. Treatments at lower pH levels and the higher Zn concentration showed significantly lower biomass, chlorophyll content, and total bacterial numbers. Bacterial heterotrophic activity did not demonstrate a statistically significant response as pH decreased, although it did show a statistically significant decrease at a concentration of 0.5 mg Zn/L. The portion of the bacterial community able to grow on nutrient agar demonstrated adaptation to the increased toxicity of Zn at lower pH levels by an increase in the proportion of bacteria resistant to Zn. In addition, the structure of the culturable bacterial community was altered at low pH, as demonstrated by a reduction in the Shannon–Wiener diversity index. The results indicate that pH can modulate Zn toxicity to the attached community.Key words: attached bacteria, zinc, heavy metal resistance, acid rain, species diversity.

ISSN:0008-4166    

DOI:10.1139/m91-083

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The rhizobial requirements and the N2-fixing potential ofPhaseolus acutifoliusandP.acutifolius×P.vulgarishybrid progeny were investigated in glasshouse experiments. AlthoughP.acutifoliuswas promiscuous, effective nodulation and N2fixation occurred only with a fewBradyrhizobiumisolates, especially those that were isolated fromP.acutifolius,P.limensis,P.penduratus,P.lunatus,Canavalia ensiformis,Calopogonium mucunoides, andPsophocarpus tetragonolobus. Strong host ×Bradyrhizobiuminteractions were detected in four genotypes ofP.acutifoliustested against eight isolates of bradyrhizobia and a commercial mixed inoculant. All seven progeny tested nodulated withBradyrhizobiumisolates andRhizobium leguminosarumbv.phaseoli, but there was a highly specific rhizobial requirement for effective nodulation and N2fixation. The progeny × rhizobial interaction accounted for 83% of the total phenotypic variation. Two (P-6 and P-7) and five (P-1, P-2, P-3, P-4, and P-5) progeny nodulated and fixed N2effectively withR.l. bv.phaseoliandBradyrhizobiumspp., respectively. TheR.l. bv.phaseoli– progeny symbiosis had a greater N2-fixing potential than theBradyrhizobiumisolate – progeny symbiosis. In a soil (oxisol) test, progeny P-6 and P-7 showed significant response to inoculation withR.l. bv.phaseoli. StrainR.l. bv.phaseoliTAL 182 was the most competitive strain, occupying 84% of the nodules in both the progeny.Key words: rhizobial requirements,Phaseolus acutifolius×Phaseolus vulgarishybrids.

ISSN:0008-4166    

DOI:10.1139/m91-084

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The metabolism of phenazopyridine was studied in the filamentous fungusCunninghamella echinulata(synonymC.bainieri) ATCC 9244. Metabolic products were initially isolated by HPLC and TLC, with further characterization achieved by a combination of GLC, NMR, mass spectrum (MS), and GC–MS analyses. Selected samples of the incubation broths were treated with (β-glucuronidase–arylsulfatase. In addition to the reported mammalian metabolitesp-aminophenol, acetaminophen, 2′-hydroxyphenazopyridine, 4′-hydroxyphenazopyridine, and parent drug, a novel metabolite was unequivocally identified as the sulfate monoester of 4′-hydroxyphenazopyridine.para-Hydroxylation of the aromatic ring with subsequent sulfoconjugation were observed as the major routes of metabolism. Ethanol, carbon monoxide, and quinidine had inhibitory effects on theC.echinulatametabolism of phenazopyridine, suppressing formation of 4′-hydroxyphenazopyridine and its sulfate monoester.Key words:Cunninghamella echinulata, biotransformation, GLC analysis of phenazopyridine, HPLC analysis of phenazopyridine, phenazopyridine, sulfate conjugate.

ISSN:0008-4166    

DOI:10.1139/m91-085

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Escherichia colistrains J53(nal) and J53(RP4) were grown together in glucose-limited continuous cultures. Based on the measured growth kinetic constants of the two strains, take-over of the cultures by J53(RP4) was predicted. However, in practice, an initial period of predominance by J53(RP4) was always followed by a prolonged period in which relative numerical proportions of the two strains oscillated widely. This period of oscillation was removed or greatly reduced when the difference between the predicted growth-rate potentials of the two strains was increased by selection of a chemostat-adapted variant of J53(RP4).Key words: competition, chemostat, plasmid,Escherichia coli.

ISSN:0008-4166    

DOI:10.1139/m91-086

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Eleven hundredBacillusstrains isolated from marine sediment from the Minas Basin, Nova Scotia, Canada, were purified on LB agar supplemented with ampicillin, chloramphenicol, erythromycin, streptomycin, tetracycline, or mercuric chloride. Seventy-seven isolates were examined for plasmid DNA, and for resistance to 11 antibiotics, HgCl2, and phenylmercuric acetate. Minimum inhibitory concentrations of Ag, Cd, Co, Cu, and Zn were also determined. Forty-three percent of antibiotic- and mercury-resistant strains contained one or more plasmids ranging from 1.9 to 210 MDa. Fifty-four percent carried plasmids greater than 20 MDa, and 97% were resistant to two or more metals. There was no correlation between plasmid content and resistance either to antibiotics or to mercurial compounds in these strains. Mercury-resistant isolates were unable to transform Hg2+to volatile Hg0by virtue of a mercuric reductase enzyme system (mer). Strains resistant to Hg2+were investigated for their ability to produce H2S and intracellular acid-labile sulfide when grown in the absence and presence of HgCl2. Lower levels of H2S and intracellular sulfide were detected only in metal-resistant strains grown in the presence of HgCl2, suggesting that cellular sulfides complexed with Hg2+in these strains.Key words:Bacillus, plasmid, antibiotic resistance, metal resistance, marine sediment.

ISSN:0008-4166    

DOI:10.1139/m91-087

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Canola (Brassica napus) has a high sulfur requirement during vegetative growth and exhibits symptoms of sulfur deficiency when cropped on Saskatchewan soils low in plant available sulfur. Elemental sulfur (S0) is frequently used as a fertilizer to alleviate this deficiency. The potential of sulfur-oxidizing microorganisms to enhance the growth of canola in S0fertilized soils was assessed. Sulfur-oxidizing bacteria and fungi were isolated from the rhizosphere and rhizoplane of canola grown in four different Saskatchewan soils under growth chamber conditions. Of 273 bacterial isolates, 245 (89.7%) oxidized S0to thiosulfate or tetrathionatein vitro, and 133 (48.7%) oxidized S0to sulfate; 70 fungal isolates oxidized S0to sulfate. Eighteen bacterial isolates demonstrating the highestin vitrosulfur oxidation were tested as seed inoculants under growth chamber conditions, with S0as sulfur source. Fourteen isolates increased canola leaf size measured at the bud stage of growth, and seven isolates increased root and pod dry weights at maturity. Three of the 14 isolates were also able to stimulate canola leaf area in the presence of plant available sulfate. The shoot material from canola inoculated with two of these isolates contained more iron, sulfur, and magnesium than uninoculated canola. Three of the 14 isolates inhibited the growth of the canola fungal pathogens,Rhizoctonia solaniAG2-1,R.solaniAG4, andLeptosphaeria maculans"Leroy." Another isolate was antagonistic towards bothR.solanistrains and another inhibited the growth ofR.solaniAG2-1 andL.maculans"Leroy." Thus some sulfur-oxidizing isolates appear to stimulate canola growth due to the enhancement of mineral nutrient uptake, whereas in other cases antibiosis towards canola pathogens may also be involved.Key words: elemental sulfur, oxidation, canola, rhizosphere, plant growth promoting rhizobacteria.

ISSN:0008-4166    

DOI:10.1139/m91-088

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

SixCampylobacter jejuniand sixCampylobacter colistrains were isolated from cows and pigs, and their survival in lake water was compared by viable counts.Campylobacter jejunisurvived longer in culturable form thanC.coliin untreated and membrane-filtered water both at 4 and 20 °C. This difference in survival time may be a reason whyC.jejuniis generally isolated from surface waters more frequently thanC.coli. Both species survived better in filtered than in untreated water. This suggests that predation and competition for nutrients affect the survival of bothCampylobacterspecies in the aquatic environment.Key words:Campylobacter jejuni,Campylobacter coli, predation, competition, survival, water.

ISSN:0008-4166    

DOI:10.1139/m91-089

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The genomic DNA of two strains of the entomopathogenic fungusBeauveria bassiana, strain GK2016, a "wild type" (virulent), and strain GK2051, a less virulent mutant to grasshoppers, was digested with 12 restriction endonucleases. Gel electrophoresis conditions were established to show restriction fragment length patterns visually in the digested DNA stained with ethidium bromide. The less virulent mutant was generated by ultraviolet illumination of conidiospores at a 95% lethal dose. Both strains of the fungi were identical in morphology as well as in 16 of 22 API-ZYM kit enzyme assays. Differences in levels of total enzyme activity were observed for esterase, esterase–lipase, (β-galactosidase, chitinase, and protease. ANeurospora crassaβ-tubulin gene (heterologous gene) and two homologous DNA probes (pJK16 and pJK18) hybridized to several specific DNA bands inB.bassianastrain GK2016 but not in strain GK2051. Strain GK2051 gave different restriction fragment length patterns when compared with its parent strain. Taken together, the data show restriction fragment length differences between the genomic DNA of the two strains, including the loss of some DNA sequences from the mutant strain, which may be involved in pathogenicity. Finally,B.bassianaGK2016 contains a β-tubulin gene with at least partial homology to that ofN.crassa.Key words: restriction fragment length polymorphism, entomopathogen,Beauveria bassiana, bioinsecticide, filamentous fungi.

ISSN:0008-4166    

DOI:10.1139/m91-090

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

We investigated the role of calcium in growth ofRhizobium frediiUSDA208 and its influence on nodulation of cv. Peking soybean. The placement and numbers of nodules on soybean roots in growth pouches is relatively insensitive to levels of Ca2+in the root zone. In contrast, adequate Ca2+in theRhizobiumculture media is essential for induction of a normal distribution of nodules on the taproot and lateral roots. Ca2+-deprived rhizobia attach in reduced numbers to soybean roots, do not initiate nodules in the most infectible region of the taproot, and induce nodules almost exclusively on lateral roots. Ca2+starvation also greatly reduces growth of USDA208 in culture, but it has little effect on exopolysaccharide production. Strain USDA208 produces two detectable45Ca2+-binding proteins in culture. A major 38-kDa bacterial protein is regulated by the availability of Ca2+, but this protein does not itself bind45Ca2+.Key words: autoregulation, nodule regulation, nodule initiation.

ISSN:0008-4166    

DOI:10.1139/m91-091

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Several spontaneous ethylenediamine-resistant mutants ofAzospirillum brasilensestrain FP2 (Sp7, NalRSmR) were isolated. Four mutants, HM053, HM14, HM26, and HM210, were found to fix nitrogen constitutively in the presence of high concentration of NH4+and to excrete NH4+derived from nitrogen fixation. They also showed lower rates of NH4+uptake than the wild-type strain, FP2. All of the mutants were prototrophic for glutamine or glutamate. Their glutamate synthase and glutamate dehydrogenase activities were similar to those of the wild-type strain. However, they presented different patterns of glutamine synthetase activity. Mutant HM14 showed low levels of normally regulated glutamine synthetase activity, while the other mutants showed low levels (HM053) or wild-type levels (HM26 and HM210) of constitutively adenylylated glutamine synthetase activity. The mutants are probably defective in the adenylylation system.Key words:Azospirillum brasilense, ammonium excretion, ethylenediamine resistance, glutamine synthetase.

ISSN:0008-4166    

DOI:10.1139/m91-092

出版商:NRC Research Press    

年代:1991

数据来源: NRC