摘要:

A genomic library consisting of 4- to 7-kbEcoRI DNA fragments fromFibrobacter succinogenes135 was constructed using a phage vector, λgtWESλB, andEscherichia coliED8654 as the host bacterium. Two positive plaques, designated λFSX101 and λFSX102, were identified. The inserts were 10.5 and 9.8 kb, respectively. A 2.3-kbEcoRI fragment that was subcloned from λFSX101 into pBR322 also showed xylanase activity. Southern blot analysis showed that the clonedEcoRI fragment containing the xylanase gene had originated fromF.succinogenes135. The cloned endo-(1,4)-β-D-xylanase gene (pFSX02) was expressed constitutively inE.coliHB101 when grown on LB and on M9 medium containing either glucose or glycerol as the carbon source. Most of the β-D-xylanase activity was located in the periplasmic space. Zymogram activity stains of nondenaturing polyacrylamide gels and isoelectric focusing gels showed that several xylanase isoenzymes were present in the periplasmic fraction of theE.coliclone FSX02 and they probably were due to posttranslational modification of a single gene product. Comparison of the FSX02 xylanase and the xylanase from the extracellular culture fluids ofF.succinogenes135 and S85 for their ability to degrade oat spelt xylan showed that, for equal units of β-D-xylanase activity, hydrolysis by the cloned gene product was more complete. However, unlike the unfractionated mixture of xylanases fromF.succinogenes135 and S85, the enzyme fromE.coliFSX02 was unable to release arabinose from oat spelt xylan.Key words: rumen bacterium, xylanase gene, λgtWESλB, cellulolysis,Fibrobacter succinogenes.

ISSN:0008-4166    

DOI:10.1139/m91-093

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Electron microscopy showed that electron-dense granules accumulated inPropionibacterium acnesin larger amounts when the bacteria were grown on a phosphate-rich medium. X-ray microanalysis demonstrated that the granules contained mostly phosphorus and potassium, indicating that the cells contained polyphosphate granules. When cells were grown on a complex Bacto-agar medium, the amount and the size of the polyphosphate granules were reduced. Polyphosphate was also detected with31P nuclear magnetic resonance (31P-NMR). Of the polyphosphates observed with31P-NMR, 20% seemed to be located outside the cell membrane. Broad-band near-ultraviolet irradiation (emission maximum 366 nm) corresponding to doses that killed 37% of the cells increased the amount of polyphosphate in cells grown on the phosphate-rich medium. The fluorescent chromophore 4′,6-diamidino-2-phenylindole (DAPI) shifted the fluorescence emission from 478 to 538 nm when bound to polyphosphate and excited at 340 nm. DAPI was used to detect polyphosphates generated after near-ultraviolet irradiation of the cells. Nonirradiated cells showed no increased fluorescence at 538 nm, indicating no polyphosphates, even if polyphosphate is present in the cells. We conclude that DAPI did not have "access" to the intracellular polyphosphate as long as the cells were not light damaged. This observation is important for the interpretation of near-UV damage to cells.Key words: electron and X-ray microscopy, fluorescence, DAPI,31P-NMR, granule.

ISSN:0008-4166    

DOI:10.1139/m91-094

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A mutant ofSalmonella choleraesuiswas identified that could invade (enter) and penetrate through polarized monolayers of Caco-2 and MDCK epithelial cells at normal levels but was defective for intracellular multiplication within these cells. It was also able to survive inside cultured J774 macrophage cells. These bacteria remained inside membrane-bound vacuoles, which coalesced at later times in the perinuclear region of the epithelial cell. This mutant exhibited slightly slower growth rates in rich or minimal media than the parental strain but was normal for iron usage, phosphate usage, and anaerobic growth and was a prototroph. The mutant was completely avirulent when administered orally or intravenously to susceptible mice. These results suggest that the ability to multiply within eukaryotic cells may contribute toS.choleraesuisvirulence.Key words:Salmonella choleraesuis, virulence, pathogenesis, intracellular, multiplication.

ISSN:0008-4166    

DOI:10.1139/m91-095

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An anaerobic bacterial consortium carboxylating phenol to benzoate by cometabolism in the presence of proteose peptone under methanogenic conditions was studied. Yeast extract or a mixture of tryptophan and lysine could replace proteose peptone without affecting the carboxylating activity, whereas glucose, glycerol, pyruvate, volatile fatty acids, and sodium bicarbonate could not. The carboxylating microorganism could not be obtained pure from the phenol culture supplemented with tryptophan and lysine; six different morphological types of microorganisms were able to grow in this medium. The results obtained with potential intermediates of benzoate degradation given as substrates to the consortium suggest that benzoate is transformed to 1-cyclohexene carboxylate and to heptanoate. Part of 1-cyclohexene carboxylate was transformed to an apparent dead-end product identified as cyclohexane carboxylate.Key words: phenol, carboxylation, benzoate, methanogenic conditions.

ISSN:0008-4166    

DOI:10.1139/m91-096

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The insertion sequence ISRm1frequently occurs inRhizobium melilotiand is a potential mutagen. Data for the frequency of ISRm1transposition in the commercial inoculant strain SU47 (containing eight copies of IsRm1) indicate that this insertion sequence does not significantly affect the ability of SU47 to occupy nodules of alfalfa (Medicago sativaL.) grown at two field sites. Thirty representative isolates from the indigenous population ofR.melilotiat each of these sites contained from 0 to 10 copies of IsRm1; there was no significant correlation between insertion sequence copy number and nodulating competitiveness, symbiotic effectiveness, or frequency of occurrence of indigenous rhizobia in nodules of plants grown at these sites. Collectively, these data suggest that ISRm1has little impact on the stability of agriculturally important properties ofR.melilotifrom the two field sites, despite its potential as a mutagen.Key words: insertion element, symbiotic effectiveness, competitiveness,Rhizobium meliloti, indigenous populations.

ISSN:0008-4166    

DOI:10.1139/m91-097

出版商:NRC Research Press    

年代:1991

数据来源: NRC