摘要:

A denitrifying bacterium capable of pyridine degradation was isolated from contaminated soil. The Gram-negative bacterium, which was identified as anAlcaligenessp., rapidly metabolized pyridine under anaerobic conditions with nitrate as electron acceptor. [14C]Pyridine was converted to14CO2, unidentified polar metabolic products, and labeled biomass. During pyridine metabolism, nitrate was reduced to nitrogen gas via nitrite and nitrous oxide. The molar ratio of pyridine to nitrate strongly affected pyridine metabolism. Maximum pyridine degradation occurred at a nitrate concentration above 5 mM, a temperature of 22–36 °C, and a pH of 6.8–8.0.Key words: pyridine, anaerobic metabolism, denitrifying bacteria,Alcaligenessp.

ISSN:0008-4166    

DOI:10.1139/m91-125

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

To understand the physiological control of attachment ofBradyrhizobium japonicum, bacterial growth and preincubation conditions were varied before exposing the bacteria (104 cfu mL−1) to excised soybean root segments. The attachment rate of strain USDA 110 was constant through a 7-h exposure (0.9% of the population attached per hour). Maximal attachment of strain USDA 110 occurred during log phase and for strains USDA 76 and USDA 31, during early stationary phase. The ability of log-phase cultures to attach to roots was significantly correlated with their competitive ability to nodulate soybean. Cells of strains USDA 110 attached to roots were isolated and reexposed to roots 15 times over a 6-month period. No significant increase in attachment ability of these serially exposed bacteria was observed (a mean of 1.4% of the population attached at each 2-h exposure). Attachment was stimulated 2.4- to 7-fold when cells of strains USDA 110 or USDA 31 were preincubated in a minus-nitrogen plant nutrient solution and on new cell growth. The stimulation of attachment could not be mimicked by preconditioning cells in solutions of NaCl, CaCl2, or CaSO4of the same normality as the nutrient solution. The ability ofB.japonicumstrains to attach to host roots is a dynamic property affected by growth medium, culture age, and cell pretreatment conditions. The progeny of attached cells adhered to roots in the same low proportions as cells not previously exposed to roots.Key words: rhizobia, adhesion, competition, bacterial pretreatment.

ISSN:0008-4166    

DOI:10.1139/m91-126

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Anin vitrochemostat system was used to study the growth and the expression of iron-regulated outer-membrane proteins (IROMPs) by biofilm cells ofPseudomonas aeruginosacultivated under conditions of iron limitation. The population of the planktonic cells decreased when the dilution rate was increased. At a dilution rate of 0.05 h−1the populations of planktonic cells of both mucoid and nonmucoidP.aeruginosawere 3 × 109cells/mL. This value dropped to 5 × 106cells/mL when the dilution rate was increased to 1.0 h−1. The reverse was observed for the biofilm cells. The number of biofilm cells colonising the silicone tubing increased when the dilution rate was increased. The number of biofilm cells of the mucoid strain at steady state was 2 × 108cells/cm (length) when the dilution rate was fixed at 0.05 h−1. The figure increased to 8 × 109cells/cm when the dilution rate was increased to 1.0 h−1. The population of biofilm cells of the nonmucoid strain was 9 × 107cells/cm (length) when the dilution rate was 0.05 h−1. It increased to 2 × 109cells/cm when the dilution rate was set at 1.0 h−1. The expression of IROMPs was induced in the biofilm cells of both mucoid and nonmucoid strains when the dilution rates were 0.05 and 0.2 h−1. IROMPs were reduced but still detectable at the dilution rate of 0.5 h−1. However, the expression of IROMPs was repressed when the dilution rate was increased to 1.0 h−1. The data suggest that the biofilm cells ofP.aeruginosaswitch on the expression of IROMPs to assist iron acquisition when the dilution rate used for the chemostat run is below 0.5 h−1. The high affinity iron uptake system is not required by the biofilm cells when the dilution rate is increased because the trace amount of iron present in the chemostat is sufficient for the growth of adherent biofilm cells.Key words:Pseudomonas aeruginosa, chemostat, iron, outer-membrane proteins, biofilm.

ISSN:0008-4166    

DOI:10.1139/m91-127

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Tungstate, at concentrations that completely suppressed nitrate reductase activity inParacoccus denitrificans, caused only partial inhibition of nitrate reductase inAzospirillum brasilenseSp7. Nitrate reductase activity in cell-free extracts was much more sensitive than whole cells to tungstate, suggesting that there may be a barrier to its transport. Nitrite reductase activity was partially inhibited by tungstate in both whole cells and cell-free extracts.Azospirillum brasilenseapparently scavenged enough contaminating molybdenum from molybdenum-limited medium to allow maximum nitrate reductase activity, which was not stimulated by added molybdate. Cells grown in molybdenum-depleted medium could not reduce nitrate. Nitrate concentrations less than 0.25 mM inhibited activity, but not synthesis, of nitrite reductase and caused significant accumulation of nitrite during reduction of nitrate.Key words:Azospirillum brasilense,Paracoccus denitrificans, nitrate reductase, nitrite reductase, tungsten, molybdenum, denitrification.

ISSN:0008-4166    

DOI:10.1139/m91-128

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Escherichia colistrains CA46(pColG) and CA58(pColH) each apparently synthesized two generally similar bactericidal colicin proteins whose molecular weights were approximately 5 500 and 100 000. These proteins were more resistant to trypsin than representative colicins A, D, E1, and V. The smooth wild-type strains harbouring plasmids pColG and pColH were serotyped O169:NM and O30:NM, respectively, being typically associated with nonpathogenicE.coliof human origin. Rough and semirough variants, which were selected using resistance to novobiocin, were intrinsically insensitive to almost as many colicins (10 tested) as their parents. For this reason the wild-type strains would not be useful for identifying colicins G and H on the basis of immunity. The O antigenic side chains of both wild-type strains shielded three of the six bacteriophage protein receptors tested.Key words: colicin, protein, plasmid, O antigen, bacteriophage.

ISSN:0008-4166    

DOI:10.1139/m91-129

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Renibacterium salmoninarumis a pathogen of salmonid fish that produces large amounts of extracellular protein (ECP) during growth. A proteolytic activity present in ECP at elevated temperatures digested the majority of the proteins in ECP. This digestion was also associated with the loss of ECP immunosuppressive function.In vitroactivity of the proteinase in ECP was temperature dependent: it was not detected in an 18-h digest at 4 and 17 °C but became readily apparent at 37 °C. Proteinase activity was detected at bacterial physiological temperatures (17 °C) in reactions incubated for several days. Under these conditions, digestion of partially purified p57, a major constituent of ECP and a major cell-surface protein, yielded a spectrum of breakdown products similar in molecular weight and antigenicity to those in ECP. This pattern of digestion suggests that most of the immunologically related constituents of ECP are p57 and its breakdown products. The proteolytic activity was sensitive to phenylmethylsulfonyl fluoride, methanol, and ethanol and to 10-min incubation at temperatures above 65 °C. Electrophoretic analysis of the proteinase on polyacrylamide gels containing proteinase substrates indicated the native form to be 100 kDa or greater. The enzyme was active against selected unrelated substrates only when coincubated with a denaturant (0.1% lauryl sulfate) and (or) a reducing agent (20 mM dithiothreitol).Key words:Renibacterium salmoninarum, proteinase, hemagglutinin, antigen F, bacterial kidney disease.

ISSN:0008-4166    

DOI:10.1139/m91-130

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A total of 144 isolates ofXanthomonas oryzaepv.oryzaewere screened for bacteriocin production against 30 indicator strains ofX.oryzaepv.oryzae. Forty isolates showed broad-spectrum inhibitory activity against 20–27 indicators, presumably because of the production of bacteriocin compounds. The selected isolates were screened for bacteriocin production at 29 °C and tested for virulence on rice differentials. Since all of the isolates were pathogenic, nonpathogenic bacteria were generated throughN-methyl-N-nitro-N-nitrosoguanidine mutagenesis and by repeated subculturing. Epiphytic colonization and survival of pathogens and of nonpathogenic bacteriocin producers on rice plants were monitored, using mutants resistant to streptomycin and rifampicin. An improved method of pathogen inoculation was developed and used to evaluate biological control. Treatment with nonpathogenic bacteriocin-producing bacteria resulted in reductions of bacterial blight incidence up to 31–99% in greenhouse tests and 11–73% in the screenhouse. Bacterial leaf streak severity was reduced 4–20% in the greenhouse and disease incidence was reduced 20–39% in the screenhouse.Key words: bacteriocin, biological control,Xanthomonas oryzaepv.oryzae, mutagenesis, rice.

ISSN:0008-4166    

DOI:10.1139/m91-131

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Enterococcus faecalisssp.liquefaciensS-48 (producer of the peptide antibiotic AS-48) and its mutant B-48-28 (AS-48−) secrete the bacteriocin Bc-48. This substance has been purified to homogeneity from culture supernatants of strain B-48-28; it consists of a protein (80 kDa) stable from pH. 5.5 to 9.0 and sensitive to temperatures above 45 °C and to proteases. Its inhibitory spectrum is restricted to strains ofEnterococcus faecalis. Bc-48 inhibits protein synthesis but does not affect amino acid uptake. A partial reduction of cell viability, together with autolysis, is also observed. Bc-48 differs from peptide AS-48 in both its molecular properties and mode of action.Key words:Enterococcus faecalis, bacteriocin, bacteriolytic.

ISSN:0008-4166    

DOI:10.1139/m91-132

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The objective of this study was to analysein vivothe effect of oxygen on the nitrogenase ofBacillus polymyxa. The culture technique employed in this study prevented spore formation byB.polymyxaduring the entire period of exposure to acetylene. Under these conditions the acetylene-reduction assay allowed quantification of nitrogenase activity over long incubation periods (44 h). Nitrogenase activity was highest in cells harvested in the late logarithmic phase. Atof 0.19 and 0.37 kPa, acetylene reduction was inhibited by 80 and 100%, respectively. This switch-off effect could be reversed through oxygen exhaustion, either by flushing the culture with N2or by cellular respiration, suggesting a respiratory protection mechanism for the nitrogenase complex inB.polymyxa. Oxygen consumption measured by a closed-chamber respirometer showed a linear increase up to aof 0.2 kPa. Above 0.3 kPa a saturation in oxygen consumption was observed. Exposure to high oxygen pressures resulted in an irreversible loss of nitrogenase activity. The oxygen inhibition pattern was shown to be similar to that in other microaerophilic and anaerobic nitrogen-fixing microorganisms.Key words:Bacillus polymyxa, nitrogenase, oxygen inhibition, reversibility, respiration.

ISSN:0008-4166    

DOI:10.1139/m91-133

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Pseudomonas cepaciaR55 and R85 andPseudomonas putidaR104, antagonistic towards plant pathogenic fungiin vitro, were assessed as seed inoculants for winter wheat (cv. Norstar) grown in a growth chamber in soil infested withFusarium solaniorRhizoctonia solaniisolate AG-1, AG 2-1, or AG-3. Infestation of soil withR.solaniAG-1 or AG 2-1 reduced root dry weight of uninoculated plants by 62 and 78%, respectively, whereasR.solaniAG-3 orF.solanihad no effect on plant biomass. Pseudomonad inoculants increased (relative to plants subjected to disease) the winter wheat root dry weight by 92–128% and shoot dry weight by 28–48% in the soil infested withR.solaniAG-1. The shoot material of all plants inoculated with pseudomonads also had significantly (P < 0.05) higher total Fe contents than the uninoculated treatment in theR.solaniAG-1 infested soil.Pseudomonas cepaciaR55 produced the highest (P < 0.01) total Fe contents in the shoots, but it had no effect on N and P content.Pseudomonas cepaciaR85 significantly increased total N (P < 0.05) and total P (P < 0.01) of wheat shoots, andP.putidaR104 increased the percentage (P < 0.05) and (or) total P content (P < 0.01) in the soil infested withR.solaniAG-1.Pseudomonas cepaciaR85 also significantly (P < 0.05) increased wheat shoot biomass inR.solaniAG-3 infested soil. All three pseudomonads produced fluorescent siderophores when cultured in a low-iron medium. These results suggest anin situantibiosis activity of three fluorescent pseudomonad strains towards phytopathogenic fungi and suggest that the plant growth response was probably due to protection against damage caused byR.solani.Key words: biocontrol, pseudomonads,Rhizoctonia solani, winter wheat, siderophores.

ISSN:0008-4166    

DOI:10.1139/m91-134

出版商:NRC Research Press    

年代:1991

数据来源: NRC