摘要:

The killer activity of 46 strains belonging to 12 yeast and yeast-like species isolated from water or sediment samples was studied. Only two strains of the genusCryptococcusdid not show killer activity. Killer activity of yeast-like speciesAureobasidium pullulans,Hyphopichia burtoniiandGeotrichum candidum, and yeast speciesCandida kruseiandCandida lambicawas low.Sporobolomyces salmonicolor,Cryptococcus laurentiiandCryptococcus albidushad better activity against basidiomycetous than ascomycetous species.Hansenula anomalastrains showed good activity againstGeotrichum candidumstrains,Cryptococcus albidus, andSporobolomyces salmonicolor.Rhodotorulaspecies showed activity against the majority of both ascomycetous and basidiomycetous species.Key words: yeasts, killer activity, sediment and water samples.

ISSN:0008-4166    

DOI:10.1139/m95-105

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The distribution of oil-degrading bacteria in the coastal water and sediments of Hokkaido, Japan, was surveyed. The potential of mixed microbial populations to degrade weathered crude oil was not confined to any ecological components (water or sediment) nor to the sampling stations. One microbial culture that was stable during repeated subculturing degraded 45% of the saturates and 20% of the aromatics present in crude oil in 10 days during the initial screening. The residual hydrocarbons in this culture were extracted by chloroform and dispersed in a fresh seawater-based medium and subsequently inoculated with microorganisms from the first culture. After full growth of the second culture, the residual hydrocarbons were again extracted and dispersed in a fresh medium in which microorganisms from the second culture had been inoculated. This sequential process was carried out six times to enrich those microorganisms that grew on the recalcitrant components of crude oil. After repeated exposure of the residual crude oil to the enriched microorganisms, about 80% of the initially added crude oil was degraded. The cultures obtained after each enrichment cycle were kept, and the degradation of fresh crude oil by the enriched microorganisms was examined. The degradative activity of the enriched cultures increased as the number of enrichment cycles increased. A microbial population that had been selected six times on the residual crude oil could degrade 70% of the saturates and 30% of the aromatics of crude oil. Thus, growth of a microbial population on residual crude oil improved its ability to biodegrade crude oil.Key words: crude oil, biodegradation, sequential enrichment, saturated hydrocarbon, aromatic hydrocarbon.

ISSN:0008-4166    

DOI:10.1139/m95-106

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The plant growth promoting rhizobacteriumPseudomonas putidaGR12-2 was originally isolated from the rhizosphere of plants growing in the Canadian High Arctic. Here we report that this bacterium was able to grow and promote root elongation of both spring and winter canola at 5 °C, a temperature at which only a relatively small number of bacteria are able to proliferate and function. In addition, the bacterium survived exposure to freezing temperatures, i.e., −20 and −50 °C. In an effort to determine the mechanistic basis for this behaviour, it was discovered that following growth at 5 °C,P.putidaGR12-2 synthesized and secreted to the growth medium a protein with antifreeze activity. Analysis of the spent growth medium, following concentration by ultrafiltration, by SDS-polyacrylamide gel electrophoresis revealed the presence of one major protein with a molecular mass of approximately 32–34 kDa and a number of minor proteins. However, at this point it is not known which of these proteins contains the antifreeze activity.Key words: plant growth promoting rhizobacteria, PGPR, bacterial fertilizer, soil bacteria, antifreeze protein.

ISSN:0008-4166    

DOI:10.1139/m95-107

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Fluoride and a variety of other weak acids acted to reduce reversibily the acid tolerance of glycolysis by intact cells ofStreptococcus mutansGS-5 as shown by higher final pH values in acid-drop experiments with glucose in excess. The order of effectiveness was fluoride > indomethacin > ibuprofen > ketoprofen > salicylate > sorbate > cinnamate >p-hydroxybenzoate > benzoate > ascorbate. Only fluoride also acted as an inhibitor of the glycolytic enzyme enolase. However, enolase in permeabilized cells was also inhibited by acidification with a sharp drop-off in activity between pH 6 and 5. It was proposed that the weak acids, including fluoride, acted to reduce glycolytic acid tolerance by enhancing cytoplasmic acidification and thereby inhibiting enzymes such as enolase. The potencies of the acids could not be predicted accurately from knowledge of pKavalues, octanol–water partition coefficients, and molecular weights. It was concluded that their modes of action in acid sensitization involved perturbations of membrane function in addition to their acting as transmembrane carriers of protons. Methylparaben (methyl ester ofp-hydroxybenzoate) was also a sensitizer but was less effective than the parent acid.Key words: fluoride, weak acids, enolase,Streptococcus mutans, glycolysis.

ISSN:0008-4166    

DOI:10.1139/m95-108

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The distribution of thestrA–strBstreptomycin-resistance (Smr) genes associated with Tn5393was examined in bacteria isolated from the phylloplane and soil of ornamental pear and tomato. Two ornamental pear nurseries received previous foliar applications of streptomycin, whereas the tomato fields had no prior exposure to streptomycin bactericides. Although the recovery of culturable Smrbacteria was generally higher from soil, the highest occurrence of Smrwas observed in phylloplane bacteria of an ornamental pear nursery that received 15 annual applications of streptomycin during the previous 2 years. Twenty-two and 12% of 143 Gram-negative phylloplane and 163 Gram-negative soil isolates, respectively, contained sequences that hybridized to probes specific for thestrA–strBSmrgenes and for the transposase and resolvase genes of Tn5393. These sequences were located on large plasmids (>60 kb) in 74% of the isolates. The 77 SmrGram-positive bacteria isolated in the present study showed no homology to the Tn5393-derived probes. Although the repeated use of a single antibiotic in clinical situations is known to favor the development of strains with resistance to other antibiotics, we found no evidence that intensive streptomycin usage in agricultural habitats favors the development of resistance to tetracycline, an antibiotic also registered for disease control on plants. The detection of Tn5393in bacteria with no prior exposure to streptomycin suggests that this transposon is indigenous to both phylloplane and soil microbial communities.Key words: streptomycin, tetracycline, antibiotic resistance, phylloplane, transposon.

ISSN:0008-4166    

DOI:10.1139/m95-109

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

InStreptomyces ambofaciens, valine favored spiramycin biosynthesis by supplying aglycone precursors. The kinetics of valine consumption and isobutyrate production showed that isobutyrate accumulated in the cell during the growth phase, was excreted in the stationary phase, and then was reassimilated during spiramycin production. When valine was in excess, its deamination led to high ammonium excretion and to a significant drop in spiramycin production. We demonstrated that ammonium ions were the cause of the negative effect. Addition of a chelator agent, Ca3(PO4)2, improved spiramycin production by sixfold. In contrast, addition of ammonium, between 0 and 48 h, severely reduced spiramycin production. The negative effect of ammonium was reversed by addition of a catabolic intermediate of valine, isobutyrate. In addition to stimulating the specific growth rate, ammonium ions slowed down valine catabolism: the specific valine uptake rate, excretion, and reassimilation of isobutyrate were lowered by the pulse of ammonium. Our study showed that in addition to valine dehydrogenase, which provided the nitrogen necessary to the cell, ammonium ions repressed ketoisovalerate dehydrogenase, which introduced valine as carbon, energy, and aglycone precursor sources. However, valine dehydrogenase and ketoisovalerate dehydrogenase did not constitute the principal enzymatic targets of the negative effect of ammonium in spiramycin production.Key words: spiramycin,Streptomyces ambofaciens, valine catabolism, ammonium.

ISSN:0008-4166    

DOI:10.1139/m95-110

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Environmental survival of human immunodeficiency virus type 1 (HIV-1) is an important public health concern. Survival of HIV in waste water is of particular interest to those who work at treatment facilities and to the general public who have contact with rivers or ocean water receiving treated sewage effluent. Other researchers have reported that HIV can be detected in waste water. Their studies, however, detected homologous nucleic acid sequences but did not attempt to determine infectivity. The current study tested primary and secondary effluent from a major metropolitan sewage agency for the presence of HIV-1 using reverse transcriptase polymerase chain reaction (RT-PCR), HIV-1 p24 antigen enzyme-linked immunosorbent assay, and infectivity testing. For RT-PCR, primers SK38/SK39 and M667/AA55 were used to identify HIV-1 RNA sequences from concentrated and extracted sewage samples. Infectivity assays employed donor peripheral blood mononuclear cells (PBMCs) stimulated with phytohemagglutinin. Coxsackievirus B4, echovirus 7, and poliovirus 1, enteroviruses normally present in sewage, were tested for replication in PBMCs. Poliovirus 1 was found to infect the PBMCs. To eliminate other enteroviruses that may also infect the PBMCs and interfere with HIV-1 testing, concentrated sewage was treated with human immunoglobulin (free of HIV antibodies) and poliovirus antisera before infectivity assays were performed. All treated sewage samples tested negative for HIV-1 by all methods used. HIV-1 seeded into sewage, however, remained infectious in the assay, indicating that the sewage water sample did not interfere with HIV infectivity nor was it toxic to the PBMCs.Key words: HIV, sewage, RT-PCR, infectivity.

ISSN:0008-4166    

DOI:10.1139/m95-111

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A genetically markedRhizobium melilotistrain, R692, was prepared by insertion of a 1.7-kb DNA segment from Tn903between thenifHDKandfixABCgenes in thenodmegaplasmid. This DNA was used as a marker, detectable by polymerase chain reaction (PCR), for the specific identification of bacteria in soil samples and alfalfa nodules. This detection technique was tested by applying different titres of the marked strain to field plots seeded with alfalfa. Samples of soil and nodules were assayed for the presence of the marker DNA fragment by PCR using primers specific to the marker sequence. The experiments revealed that the bacteria could be detected directly in soil containing about 103–104bacteria/g, but greater sensitivity was prevented by potent PCR inhibitors present in the samples. The titre of the bacteria in the soil decreased rapidly after inoculation, dropping about 10-fold per week. Tests of vertical location of the bacteria in soil cores showed that the bacteria were initially dispersed to a depth of 18 cm, and subsequently retained viability in the top 2–8 cm. As few as 10 markedR.melilotiper gram of soil resulted in its establishment at detectable levels in nodules. Application of about 104–105bacteria/g soil was sufficient to give the maximum number of nodules per plant and resulted in 70–90% occupancy by the marked strain. Limited movement of the inoculant was detected by analysis of nodules from plants adjacent to the sites where the bacteria were applied, probably by movement in water. The experiments demonstrated the advantages of PCR for the monitoring of marked microorganisms in the environment.Key words: genetically engineered microorganism, PCR inhibitor, nitrogen fixation,nifandfixgenes, genetic marker.

ISSN:0008-4166    

DOI:10.1139/m95-112

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

All the mutacins described so far have been shown to be different substances. To classify 86 mutacinogenic strains, we determined their activity spectra towards 12 standard oral streptococci and towards themselves, using a deferred antagonism test. The mutacinogenic strains could be grouped into 15 mutacinotypes according to their activity spectra against the 12 standard oral streptococci. By combining the results of their activity spectra and their sensitivity patterns amongst themselves, we defined 24 mutacin groups. Using the 24 type strains corresponding to these groups as producers and as indicators, it will be easier to classify new mutacin-producing isolates.Key words: bacteriocin, mutacin,Streptococcus mutans, inhibitory substance.

ISSN:0008-4166    

DOI:10.1139/m95-113

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

FourteenLactococcus lactisstrains showing inhibitory activity againstListeria innocuaSICC 4202 were isolated from different French raw milks and raw milk cheeses and screened for bacteriocin production by the triple layer method under conditions that eliminate the effects of lactic acid and hydrogen peroxide. Three bacteriocinogenic strains (twoLactococcus lactissubsp.lactisbv.diacetylactisUL719 and UL720 and oneLactococcus lactissubsp.lactisUL730) were selected for their high capacity to inhibit the growth of various food pathogens, includingListeria monocytogenes,Staphylococcus aureus, and clostridial strains. The inhibitory compounds from these three strains are inactivated by selected proteases, indicating their protein nature. They retained their antibacterial activity after heat treatments of 100 °C for 60 min and 121 °C for 20 min, and in the pH range from 2 to 11. The bacteriocin diacetin B produced by strain UL720 has been purified by a pH-dependent adsorption–desorption procedure, followed by reverse-phase high performance liquid chromatography, with a yield of 1.25% of the original activity. Mass spectrometry analysis indicates that the pure peptide has a molecular mass of 4292.32 or 4490.28 Da, while amino acid sequencing allowed the identification of the primary structure of the bacteriocin composed of 37 amino acid residues. The structure of the peptide did not show similarity with other known bacteriocins from lactic acid bacteria.Key words: isolation,Lactococcus lactissubsp.lactisbv.diacetylactis, bacteriocin, diacetin B, purification.

ISSN:0008-4166    

DOI:10.1139/m95-114

出版商:NRC Research Press    

年代:1995

数据来源: NRC