摘要:

The plasmid profiles of oxytetracycline- and streptomycin-resistant isolates ofAeromonas salmonicida,Vibrio anguillarum, andVibrio ordaliiwere examined by agarose gel electrophoresis. Bacterial isolates were from disease outbreaks in fish on the Atlantic and Pacific coasts. Resistant isolates were examined when grown in the presence and absence of antibiotic. Alkaline lysis methods were used for plasmid isolation.Vibriospp. were predominantly plasmidless, except for a 47-kilobase (kb) plasmid. Atlantic coast isolates ofA.salmonicidapossessed four or six plasmids, with four smaller plasmids ranging in size from 4.3 to 8.1 kb being consistently observed. The plasmid profiles of antibiotic-sensitive ATCC strains were identical. The plasmid profiles of the Pacific coast isolates ofA.salmonicidavaried slightly from those of the Atlantic coast isolates with six plasmids observed, ranging in size from 4.2 to 8.9 kb. Resistance to the antibiotics was not altered following plasmid curing experiments and resistance was not transferable toEscherichia coli. Thus, resistance to oxytetracycline and streptomycin did not appear to be plasmid mediated.Key words: plasmids, antibiotics,Aeromonas,Vibrio, fish.

ISSN:0008-4166    

DOI:10.1139/m95-029

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The gene encoding bacteriocin 28b fromSerratia marcescensN28b (bssgene) has been cloned inEscherichia coliand its nucleotide sequence has been determined. The genetic determinants coding for other well-characterized bacteriocins from enterobacteria (colicins) are located in plasmids and they have always been shown to contain a gene responsible for immunity located downstream from the bacteriocin structural gene. In some cases there is another gene located downstream from the immunity gene, which is responsible for bacteriocin release. Analysis of bacteriocin 28b release and the sensitivity to this bacteriocin ofE.colistrains harbouring recombinant plasmids containing thebssgene showed that bacteriocin 28b is not released from the cell in these strains and that their phenotypic insensitivity is not associated with any region close to the structural gene. The nucleotide sequence of the region downstream from thebssgene contains two putative open reading frames transcribed in the opposite direction to thebssgene. These open reading frames apparently encode proteins that seem not to be involved in bacteriocin immunity or release. Moreover, aS.marcescensN28b genomic library was screened and no immunity gene was found. Therefore, bacteriocin 28b differs greatly from the bacteriocins from other enterobacteria, and in the following senses it is unique: firstly, the gene encoding bacteriocin 28b seems to be located on the chromosome, and secondly, insensitivity to this bacteriocin inS.marcescensN28b is not associated with the expression of an immunity gene.Key words: bacteriocin, pore-forming colicins, immunity,Serratia marcescens.

ISSN:0008-4166    

DOI:10.1139/m95-030

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Denitrification byFlexibacter canadensiswas investigated by measuring the production and (or) consumption of nitrite, nitric oxide (NO), and nitrous oxide (N2O) under anaerobic conditions. Carbonyl cyanidem-chlorophenylhydrazone (CCCP), carbonyl cyanidep-trifluoromethoxyphenylhydrazone (FCCP), 2,4-dinitrophenol, and nigericin, but not valinomycin-K+inhibited the production of nitrite and N2O from nitrate by intact cells. However, CCCP, FCCP, 2,4-dinitrophenol, nigericin, and valinomycin-K+did not affect nitrite production from nitrate by cell-free extracts. These results suggest that nitrate transport was dependent on the transmembrane pH gradient but not on the membrane potential. CCCP, FCCP, and nigericin but not 2,4-dinitrophenol and valinomycin-K+caused NO accumulation during the reduction of nitrite, and also inhibited NO consumption and N2O production from nitrite by intact cells. These results preclude an explanation for NO accumulation based on the collapse of the proton motive force by ionophores, and imply that CCCP, FCCP, and nigericin perhaps dissociated a nitrite reductase–nitric oxide reductase complex, and (or) inhibited nitric oxide reductase specifically. 2,4-Dinitrophenol and CCCP did not inhibit the reduction of N2O to dinitrogen. Addition of ≤ 1.16 μM dissolved NO did not affect the production of nitrite from nitrate, or the disappearance of nitrite or N2O. The rate of NO consumption was linear with concentrations of dissolved NO up to 67 nM. Above 67 nM NO, NO consumption was inhibited, suggesting that NO is toxic to nitric oxide reductase.Key words: ionophores, denitrification, nitric oxide,Flexibacter canadensis.

ISSN:0008-4166    

DOI:10.1139/m95-031

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The rhizosphere of wetland rice has significant N2-fixing activity. It has been suggested that N2fixation in the rice root zone is associated with the activity of various N2-fixing heterotrophic bacteria that inhabit the rice rhizosphere. Because of the generic diversity, many different isolation media and conditions are required to count and isolate these bacteria. In an attempt to overcome any bias from culture-dependent methods we amplifiednifDsegments from crude rice root DNA by the polymerase chain reaction. ThenifDfragments were then cloned into a pT7 BlueT-vector to construct anifDlibrary. Sixteen clonednifDgenes chosen at random from the library were sequenced. A comparison with published sequences indicated the presence of seven novel groups of NifD proteins, which implies the existence of at least seven components in the diazotrophic community of rice roots, dominated mainly by proteobacteria. We also observed genetic variability within the clusters, which suggests the coexistence of many closely related bacterial lineages. However, we did not findAzospirillum-likenifDclones, although many reports indicated the widespread presence ofAzospirillumspp. Therefore, it remains to be clarified whetherAzospirillumspecies are the widespread N2-fixing bacteria in rice roots.Key words: N2fixation, molecular evolution,nifD, rice rhizosphere.

ISSN:0008-4166    

DOI:10.1139/m95-032

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Uptake of fructose by intact cells ofHaloferax volcanii, one of the sugar-utilizing halobacteria, was examined with the following results. (i) The fructose transporter was inducible, (ii) Kinetic analysis showed aKtof 0.37 μM and aVmaxof 4.61 nmol∙mg protein−1∙min−1. For a glucose transport system in this bacterium,Ktwas 12.5 μM, showing that the fructose transporter had a much larger affinity for a substrate than the glucose transporter, (iii) No uptake was observed by the envelope vesicles, (iv) Phloridzin and phloretin inhibited fructose transport, although a relatively higher concentration was required than that needed to inhibit glucose uptake, (v) The driving force for fructose transport was a Na+electrochemical potential gradient, (vi) Glucose and fructose were interchangeable and this conversion led to the expression of the glucose transporter even when fructose was used as the sole carbohydrate, and vice versa.Key words: glucose uptake, symport with Na+, phloridzin, phloretin,Haloferax volca

ISSN:0008-4166    

DOI:10.1139/m95-033

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Ninety-five bacterial isolates were recovered from 38 of 77 apples that had been stored at 1 °C for 6–7 months. The highest number of bacteria were recovered in nutrient, dextrose, and V8 juice broths, respectively. The bacteria were screened as biocontrol agents on cultivar Red Delicious apples primarily for control of blue mold caused byPenicillium expansum. Three bacteria effective againstP.expansumwere also tested againstBotrytis cinereafor control of gray mold. Ten, four, and five isolates significantly reduced blue mold decay when apples were stored at 5, 10, and 20 °C. Two isolates tested against gray mold decay significantly reduced decay at 5 and 10 °C and one isolate was effective at 20 °C. Thirty-six isolates that had been selected for identification by the Biolog Microstation™ System were Gram positive and contained endospores, and 30 of these were positively identified asBacillusspp. Further testing of 15 isolates that were effective biocontrol agents identified 7 asBacillus subtilison the basis of 15 microbiological tests used for determining species within the genusBacillus.Key words: endophytic, bacteria, biocontrol, postharvest.

ISSN:0008-4166    

DOI:10.1139/m95-034

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

An ultrastructural and cytochemical investigation of the development ofPhellinus noxius, a white-rot fungus, in wood chips ofBetula papyriferawas done to gain insight into the cellular mechanisms of wood cell wall degradation. Extracellular sheaths and microhyphae were seen to be involved in wood colonization. Close association was observed between these fungal structures and wood cell walls at both early and advanced stages of wood alteration. Fungal sheaths were often seen deep inside host cell walls, sometimes enclosing residual wood fragments. Investigations using gold probes indicated the occurrence of β-1,3-glucans within the fungal sheaths, while β-1,4-glucans were detected only within the fungal septa. The positive reaction with the PATAg test revealed that polysaccharides such as β-1,6-glucans were important components of the sheath. Chitin, pectin, β-glucosides, galactosamine, mannose, sialic acid, fucose, and fimbrial proteins were not found to be present in the sheath. Our data suggest that extracellular sheaths and microphyphae produced byP.noxiusduring wood cell wall colonization play an important role in wood degradation.Key words: cellulose,Phellinus, sheath, wood degradation.

ISSN:0008-4166    

DOI:10.1139/m95-035

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A methanogenic consortium transforming phenol to benzoic acid was submitted to different treatments to characterize the carboxylating microorganisms and eventually to facilitate their isolation. Under aerobic conditions, phenol was not transformed by the consortium and no growth was observed on solid medium. The consortium from an inoculum that was treated with heat, or heat and ethanol, retained the ability to carboxylate phenol under strictly anaerobic conditions. Electron microscopic observations of the consortium from an inoculum that was heated for 15 min at 80 °C revealed only Gram-positive bacilli. In this culture, methane production was not detected and benzoic acid accumulated. Five colonies with distinct morphologies were isolated from this culture on solid medium. Four of these strains were identified asClostridiumspp. In contrast to the untreated culture, none of the strains isolated were able to carboxylate phenol in pure culture or in coculture, nor could they decarboxylate or dehydroxylate 4-hydroxybenzoic acid, or oxidize 2-hydroxybenzyl alcohol, orO-demethylate anisole or 2-methoxyphenol. Also, the consortium from a treated inoculum retained its ability to decarboxylate and dehydroxylate 4-hydroxybenzoic acid forming phenol and benzoic acid, respectively, but could not accomplish the other reactions. These results suggest that spore-forming microorganisms are involved in the carboxylation of phenol and in the decarboxylation and dehydroxylation of 4-hydroxybenzoic acid.Key words: spore-forming bacteria, phenol, benzoic acid, methanogenic conditions, carboxylation.

ISSN:0008-4166    

DOI:10.1139/m95-036

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The indirect fluorescent-antibody technique has been used to establish the pattern of polar extension in the fission yeastSchizosaccharomyces pombe160 over a complete cell cycle in liquid medium, thus avoiding the possibility of perturbations being introduced by growth on an agar pad, which is the technique used in most other investigations. Nearly all of the cells (about 98%) showed more growth at the old end than at the new end that was formed by cleavage of the septum at the previous division. Importantly, there was no evidence of the abnormal growth pattern (i.e., the significant contribution of new ends to extension) in cells ofS.pombegrowing on agar pads reported by Miyata et al. (H. Miyata, M. Miyata, and B.F. Johnson. 1986. Can. J. Microbiol. 32: 528–530 and 1990. Can. J. Microbiol. 36: 390–394). In addition, extension over the cycle was inversely related to birth length (cells shorter than the mean at birth tended to produce daughter cells longer than themselves and vice versa), there was a small but significant asymmetry in the position of the septum, and the time of initiation of extension at the new end was estimated at about 0.24 of the cycle.Key words:Schizosaccharomyces pombe, fission yeast, cell-wall extension, end growth, cell cycle.

ISSN:0008-4166    

DOI:10.1139/m95-037

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Two species of photosynthetic sulphur bacteria,Chlorobium phaeobacteroidesandChlorobium limicola, found growing under different environmental conditions in the Kinneret, were cultured in the laboratory under various orthophosphate (Pi) concentrations and light intensities. Growth was followed using direct ceil counts, protein content, and pigment content. In general, the same growth pattern was shown by all three parameters and the final cell yields of both species were dependent on ambient Pi concentrations.Chlorobium limicolacompensated for low light intensities by increasing pigment production. In addition, light (but not apparently the Pi concentration) influenced the lag period of these cells, with a longer lag observed at lower light intensities. Intra- and extra-cellular activities of both acid and alkaline phosphatases were generally detected in both bacterial species. As Pi levels dropped, both the intra- and extra-cellular activities of acid and alkaline phosphatases increased, suggesting that both enzymes were inducible, although the interaction of P and light limitations was often complex. At high Pi concentrations, residual activities of both acid and alkaline phophatases were detected, probably reflecting the activity of constitutive enzymes not involved in P nutrition of the cells. Extracellular acid and alkaline phophatase activities were low and approximately constant at all light levels. Intracellular activities were relatively high and influenced by light, exhibiting saturation kinetics, and suggest that alkaline phosphatase is more sensitive to light than acid phosphatase. At low Pi concentrations, intracellular phosphatase activities were high and approximately constant over the range of light intensities examined, whereas activities of the extracellular enzymes were low but increased at lower light levels.Key words: photosynthetic bacteria,Chlorobium phaeobacteroides,Chlorobium limicola, growth, phosphate concentration, phosphatases.

ISSN:0008-4166    

DOI:10.1139/m95-038

出版商:NRC Research Press    

年代:1995

数据来源: NRC