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1.
Gnotobiotic systems were used to assess the competitive abilities of bioluminescent Sinorhizobium meliloti strains L1 (RecA−) and L33 (RecA+) for growth and host plant nodulation in the presence of a reconstructed S. meliloti population. Three wild-type strains belonging to infective subgroups of a natural S. meliloti population were chosen as competitors in microcosm studies. Whereas the RecA+ strain L33 dominated the reconstructed population with respect to growth and alfalfa nodulation, the competitiveness of the
RecA− strain L1 was reduced compared to that of one of the field strains, but comparable to that of the other field isolates. This
result indicates that strain L1, despite its recA mutation, has the potential to compete successfully with a resident S. meliloti population after environmental release.
Received: 4 November 1996 / Received revision: 9 January 1997 / Accepted: 17 January 1997 相似文献
2.
Early Infection and Competition for Nodulation of Soybean by Bradyrhizobium japonicum 123 and 138 总被引:2,自引:1,他引:1
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Interactions of soybean with Bradyrhizobium japonicum 123 (serogroup 123) and 138 (serogroup c1) were used to examine the relationship between early infection rates, competition for nodulation, and patterns of nodule occupancy. Both strains formed more infections in autoclaved soil (sterile soil) than in untreated soil (unsterile soil). Inoculation did not increase numbers of infection threads in unsterile soil-grown plants, where infection of proximal portions of primary roots was complete by 5 days after planting. Both strains infected and nodulated at similar rates in sterile soil. Nodules were always clustered on the upper root system, regardless of inoculation and soil treatment. Sixty-seven percent of the nodules of uninoculated plants grown in unsterile soil were occupied by rhizobia belonging to serogroups other than 123 or c1. Inoculation with strain 123 or 138 increased occupancy by that strain at the expense of residency by other rhizobia. Eighty-three percent of all nodules on plants dually inoculated with both strains in sterile soil contained strain 138. The corresponding value for plants inoculated in unsterile soil was 31%. Neither inoculum strain dominated occupancy of first-formed nodules in unsterile soil. It appears that north central Missouri soil may not have populations of highly competitive serogroup 123 and that early infection and nodulation rates do not contribute to the competitive success of strain 138. 相似文献
3.
Alfalfa (Medicago sativa L.) suspension cultures respond to yeast elicitors with a strong alkalinization of the culture medium, a transient synthesis
of activated oxygen species, and typical late defence reactions such as phytoalexin accumulation and increased peroxidase
activity. The alkalinization reaction as well as the oxidative burst were also observed when tobacco (Nicotiana tabacum L.) cell-suspension cultures were treated with yeast elicitors. Depending on the degree of polymerization, N-acetyl chitin oligomers induced the alkalinization response in both plant cell-suspension cultures, while only tobacco cell
cultures developed an oxidative burst. Suspension-cultured tobacco cells responded to Sinorhizobium meliloti nodulation factors with a maximal alkalinization of 0.25 pH units and a remarkable oxidative burst. In contrast, addition
of Sinorhizobium meliloti nodulation factors to suspension-cultured alfalfa cells induced a slight acidification of the culture medium, instead of
an alkalinization, but no oxidative burst.
Received: 23 November 1998 / Accepted: 23 June 1999 相似文献
4.
Corrosion inhibition by aerobic biofilms on SAE 1018 steel 总被引:5,自引:0,他引:5
Carbon steel (SAE 1018) samples were exposed to complex liquid media containing either the aerobic bacterium Pseudomonas fragi or the facultative anaerobe Escherichia coli DH5α. Compared to sterile controls, mass loss was consistently 2- to 10-fold lower in the presence of these bacteria which
produce a protective biofilm. Increasing the temperature from 23 °C to 30 °C resulted in a 2- to 5-fold decrease in corrosion
inhibition with P. fragi whereas the same shift in temperature resulted in a 2-fold increase in corrosion inhibition with E. coli DH5α. Corrosion observed with non-biofilm-forming Streptomyces lividans TK24 was similar to that observed in sterile media. A dead biofilm, generated in situ by adding kanamycin to an established biofilm, did not protect the metal (corrosion rates were comparable to those in the
sterile control), and mass loss in cell-free, spent Luria-Bertani (LB) medium was similar to that in sterile medium. Confocal
laser scanning microscopy analysis confirmed the presence of a biofilm consisting of live and dead cells embedded in a sparse
glycocalyx matrix. Mass-loss measurements were consistent with microscopic observations of the metal surface after 2 weeks
of exposure, indicating that uniform corrosion occurred. The biofilm was also able to withstand mild agitation (60 rpm), provided
that sufficient time was given for its development.
Received: 3 May 1996 / Received revision: 8 August 1996 / Accepted: 24 August 1996 相似文献
5.
Bacterial Growth Rates and Competition Affect Nodulation and Root Colonization by Rhizobium meliloti 总被引:2,自引:1,他引:1
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The addition of streptomycin to nonsterile soil suppressed the numbers of bacterial cells in the rhizosphere of alfalfa (Medicago sativa L.) for several days, resulted in the enhanced growth of a streptomycin-resistant strain of Rhizobium meliloti, and increased the numbers of nodules on the alfalfa roots. A bacterial mixture inoculated into sterile soil inhibited the colonization of alfalfa roots by R. meliloti, caused a diminution in the number of nodules, and reduced plant growth. Enterobacter aerogenes, Pseudomonas marginalis, Acinetobacter sp., and Klebsiella pneumoniae suppressed the colonization by R. meliloti of roots grown on agar and reduced nodulation by R. meliloti, the suppression of nodulation being statistically significant for the first three species. Bradyrhizobium sp. and “Sarcina lutea” did not suppress root colonization nor nodulation by R. meliloti. The doubling times in the rhizosphere for E. aerogenes, P. marginalis, Acinetobacter sp., and K. pneumoniae were less and the doubling times for Bradyrhizobium sp. and “S. lutea” were greater than the doubling time of R. meliloti. Under the same conditions, Arthrobacter citreus injured alfalfa roots. We suggest that competition by soil bacteria reduces nodulation by rhizobia in soil and that the extent of inhibition is related to the growth rates of the rhizosphere bacteria. 相似文献
6.
H. De Wever S. De Cort I. Noots H. Verachtert 《Applied microbiology and biotechnology》1997,47(4):458-461
2-Hydroxybenzothiazole (OBT) is present in wastewaters from the industrial production of the rubber vulcanization accelerator
2-mercaptobenzothiazole (MBT). We have achieved the first isolation of axenic bacterial cultures capable of the degradation
of OBT and growth on this substrate as the sole source of carbon, nitrogen and energy. All isolates had similar characteristics
corresponding to one particular isolate, which was studied in more detail and identified as Rhodococcus rhodochrous. The strains were also capable of degrading benzothiazole (BT) but not MBT or benzothiazole-2-sulphonate (BTSO3). OBT was degraded at a concentration of up to 600 mg · l−1. BT was toxic above 300 mg · l−1. MBT inhibited OBT degradation. Growth on OBT was not significantly different at pH values of between 6.3 and 7.9 or salt
concentrations between 1 % and 3 %. In shake flasks the cells clumped together, which resulted in a lower rate of oxygen transfer
and slower degradation as compared to cells grown on OBT in a stirred reactor.
Received: 22 August 1996 / Received revision: 29 November 1996 / Accepted: 29 November 1996 相似文献
7.
Axenic aerobic biofilms inhibit corrosion of SAE 1018 steel through oxygen depletion 总被引:1,自引:0,他引:1
A. Jayaraman E. T. Cheng J. C. Earthman T. K. Wood 《Applied microbiology and biotechnology》1997,48(1):11-17
Corrosion inhibition of SAE 1018 steel by pure-culture biofilms of Pseudomonas fragi and Escheri-chia coli DH5α has been evaluated in complex Luria-Bertani medium, seawater-mimicking medium, and modified Baar's medium at 30 °C.
In batch cultures, both bacteria inhibited corrosion three to six fold compared to sterile controls, and the corrosion was
comparable to that observed in anaerobic sterile media. To corroborate this result, a continuous reactor and electrochemical
impedance spectroscopy were used to show that both P. fragi K and E. coli DH5α decreased the corrosion rate by 4- to 40-fold as compared to sterile controls; this matched the decrease in corrosion
found with sterile medium in the absence of oxygen and with E. coli DH5α grown anaerobically. In addition, the requirement for live respiring cells was demonstrated by the increase in the corrosion
rate that was observed upon killing the P. fragi K biofilm in continuous cultures, and it was shown that fermentation products do not cause an increase in corrosion. Hence,
pure-culture biofilms inhibit corrosion of SAE 1018 steel by depleting oxygen at the metal surface.
Received: 16 December 1996 / Received revision: 18 March 1997 / Accepted: 27 March 1997 相似文献
8.
Summary Four species of annual medics showed poor growth and little or no nodulation in an inoculated, acid soil low in available
phosphorus. Nodulation was significantly increased by adding phosphorus to the soil. The number of nodules found on the roots
of each species was approximately the same for soil at pH 5.5 or 6.8.
A commercial inoculant ofRhizobium meliloti was adequate for nodulation of all four species and two strains of rhizobia predominated in the nodules which were assayed
by immunodiffusion. 相似文献
9.
N. Christiansen S. R. Christensen E. Arvin B. K. Ahring 《Applied microbiology and biotechnology》1997,47(1):91-94
Reductive dechlorination of tetrachloroethene was studied in a mesophilic upflow anaerobic sludge blanket reactor. Operating
the reactor in batch mode the dynamic transformation of tetrachloroethene, trichloroethene and dichloroethene (DCE) was monitored.
Tetrachloroethene was reductively dechlorinated to trichloroethene, which again was dechlorinated at the same rate as DCE
was produced. DCE showed a lag period of 40 h before transformation was observed. During normal reactor operation trans-1,2-DCE was the major DCE isomer, followed by cis-1,2-DCE. Small amounts of 1,1-DCE but no vinyl chloride were detected. When the influent tetrachloroethene concentration
was increased from 4.6 μM to 27 μM, the transformation rate increased, indicating that the system was not saturated with tetrachloroethene.
The main organic component in the effluent was acetate, indicating that the aceticlastic methane-producing bacteria were inhibited
by the chlorinated ethenes.
Received: 29 July 1996 / Received revision: 13 September 1996 / Accepted: 13 September 1996 相似文献
10.
Insertion sequence (IS) hybridization was used to define the structure of a population of Rhizobium meliloti isolated directly from soil and from nodules of Medicago sativa (alfalfa) and Melilotus alba (sweet clover) grown under controlled conditions and inoculated with a suspension of the same soil. The detection of R. meliloti isolated from soil on agar plates was facilitated by use of a highly species specific DNA probe derived from ISRm5. All R. meliloti obtained directly from soil proved to be symbiotic (i.e. nodulated and fixed nitrogen with alfalfa). Analysis of 293 R. meliloti isolates revealed a total of 17 distinct IS genotypes of which 9, 9 and 15 were from soil, M. alba and M. sativa, respectively; 8 genotypes were common to soil and both plant species. The frequency of R. meliloti genotypes from soil differed markedly from that sampled from nodules of both legume species: 5 genotypes represented about 90% of the isolates from soil whereas a single genotype predominated among isolates from nodules accounting for more than 55% of the total. The distribution of genotypes differed between M. sativa and M. alba indicating species variation in nodulation preferences for indigenous R. meliloti. The data are discussed in the context of competition for nodulation of the host plant and the selection of Rhizobium strains for use in legume inoculants. This study has ecological implications and suggests that the composition of R. meliloti populations sampled by the traditionally used host legume may not be representative of that actually present in soil. 相似文献
11.
A. M. Fauzi David J. Hardman Alan T. Bull 《Applied microbiology and biotechnology》1996,46(5-6):660-666
The degradation of low concentrations of 1,3-dichloro-2-propanol (1,3-DCP) and related halohydrins by whole cells and cell-free
extracts of soil bacteria has been investigated. Three bacteria (strains A1, A2, A4), isolated from the same soil sample,
were distinguished on the basis of cell morphology, growth kinetics and haloalcohol dehalogenase profiles. Strain A1, probably
an Agrobacterium sp., dehalogenated 1,3-DCP with the highest specific activity (0.33 U mg protein−1) and also had the highest affinity for 1,3-DCP (K
m, 0.1 mM). Non-growing cells of this bacterium dehalogenated low concentrations of 1,3-DCP with a first-order rate constant
(k
1) of 1.13 h−1 . The presence of a non-dehalogenating bacterium, strain G1 (tentatively identified as Pseudomonas mesophilius), did not enhance the dehalogenation rate of low 1,3-DCP concentrations. However, the mixed-species consortium of strains
A1 and G1 had greater stability than the mono-species culture at DCP concentrations above 1.0 gl−1.
Received: 30 April 1996 / Received revision: 30 July 1996 / Accepted: 5 August 1996 相似文献
12.
M. Wenk T. Baumgartner J. Dobovšek T. Fuchs J. Kucsera J. Zopfi G. Stucki 《Applied microbiology and biotechnology》1998,49(5):624-630
The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied
and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria
added to the soil. In soil slurry, 6 mg atrazine kg soil−1 was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil−1 and within 5 days when 0.003 g kg soil−1 was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil−1 was eliminated within 2 days by 1 g biomass kg soil−1 and within 25 days when 0.01 g biomass kg soil−1 was used. In unsaturated soil, about 60% [U-ring-14C]atrazine was converted to 14CO2 within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated
but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were
still active after a starvation period of 240 days: 15 mg newly added atrazine kg soil−1 was eliminated within 5 days.
Received: 31 October 1997 / Received revision: 16 January 1998 / Accepted: 18 January 1998 相似文献
13.
Despite the availability of many mutants for signal transduction, Arabidopsis thaliana guard cells have so far not been used in electrophysiological research. Problems with the isolation of epidermal strips and
the small size of A. thaliana guard cells were often prohibiting. In the present study these difficulties were overcome and guard cells were impaled with
double-barreled microelectrodes. Membrane-potential recordings were often stable for over half an hour and voltage-clamp measurements
could be conducted. The guard cells were found to exhibit two states. The majority of the guard cells had depolarized membrane
potentials, which were largely dependent on external K+ concentrations. Other cells displayed spontaneous transitions to a more hyperpolarized state, at which the free-running membrane
potential (Em) was not sensitive to the external K+ concentration. Two outward-rectifying conductances were identified in cells in the depolarized state. A slow outward-rectifying
channel (s-ORC) had properties resembling the K+-selective ORC of Vicia faba guard cells (Blatt, 1988, J Membr Biol 102: 235–246). The activation and inactivation times and the activation potential,
all depended on the reversal potential (Erev) of the s-ORC conductance. The s-ORC was blocked by Ba2+ (K1/2 = 0.3–1.3mM) and verapamil (K1/2 = 15–20 μM). A second rapid outward-rectifying conductance (r-ORC) activated instantaneously upon stepping the voltage to
positive values and was stimulated by Ba2+. Inward-rectifying channels (IRC) were only observed in cells in the hyperpolarized state. The activation time and activation
potential of this channel were not sensitive to the external K+ concentration. The slow activation of the IRC (t1/2 ≈ 0.5 s) and its negative activation potential (Vthreshold = −155 mV) resemble the values found for the KAT1 channel expressed in Saccharomyces cerevisiae (Bertl et al., 1995, Proc Natl Acad Sci USA 92: 2701–2705). The results indicate that A. thaliana guard cells provide an excellent system for the study of signal transduction processes.
Received: 28 March 1996 / Accepted: 11 November 1996 相似文献
14.
M. Graf A. Brunella M. Kittelmann K. Laumen O. Ghisalba 《Applied microbiology and biotechnology》1997,47(6):650-657
A new amidohydrolase deacetylating several N-acetyl-1-phenylethylamine derivatives (R)-specifically was found in Arthrobacter aurescens AcR5b. The strain was isolated from a wet haystack by enrichment culture with (R)-N-acetyl-1-phenylethylamine as the sole carbon source. (R) and (S )-N-acetyl-1-phenylethylamine do not serve as inducers for acylase formation. By improving the growth conditions the enzyme production
was increased 47-fold. The amidohydrolase was purified to homogeneity leading to a 5.2-fold increase of the specific activity
with a recovery of 67%. A molecular mass of 220 kDa was estimated by gel filtration. Sodium dodecyl sulfate/polyacrylamide
gel electrophorosis shows two subunits with molecular masses of 16 kDa and 89 kDa. The optimum pH and temperature were pH 8
and 50 °C, respectively. The enzyme was stable in the range of pH 7–9 and at temperatures up to 30 °C. The enzyme activity
was inhibited by Cu2+, Co2+, Ni2+, and Zn2+, and this inhibition was reversed by EDTA.M
Received: 20 September 1996 / Received version: 23 December 1996 / Accepted: 30 December 1996 相似文献
15.
Novotný C Erbanová P Cajthaml T Rothschild N Dosoretz C Sasek V 《Applied microbiology and biotechnology》2000,54(6):850-853
Growth parameters, ligninolytic enzyme activities and ability to degrade polycyclic aromatic hydrocarbons by the fungus Irpex lacteus were characterized and compared with those of other white rot fungi capable of rapid decolorization of poly R-478 and Remazol
Brilliant Blue R dyes. I. lacteus was able to grow on mineral and complex media and efficiently colonized sterile and non-sterile soil by exploratory mycelium
growing from a wheat straw inoculum. In shallow stationary cultures growing on high nitrogen mineral medium containing 45 mM
ammonium as nitrogen source, the fungus produced lignin peroxidase (LIP), Mn-dependent peroxidase (MnP) and laccase simultaneously,
the respective maximal activities of 70, 970 and 36 U/l being attained around day 18. Growing in nitrogen-limited medium (2.4 mM
ammonium), no LIP was formed and levels of MnP and laccase decreased significantly. During growth in sterile soil, the fungus
synthesized LIP and laccase but not MnP. I. lacteus efficiently removed three- and four-ringed PAHs from liquid media and artificially spiked soil. The variety of ligninolytic
enzymes, robust growth, capability of soil colonization and resistance to inhibitory action of soil bacteria make I. lacteus a suitable fungal organism for use in bioremediation.
Received: 30 March 2000 / Accepted: 19 May 2000 相似文献
16.
N. Sriubolmas W. Panbangred S. Sriurairatana V. Meevootisom 《Applied microbiology and biotechnology》1997,47(4):373-378
Various concentrations of isopropyl β-d-thiogalactopyranoside (IPTG) were used to induce production of the enzyme penicillin G acylase by recom binant Escherichia coli harboring plasmid pQEA11. The plasmid pQEA11 carries a wild-type pga gene, which is under the control of the tac promoter and lacI q. At low IPTG concentrations (0.025 – 0.1 mM), enzyme activity increased with increasing IPTG concentrations. At higher IPTG
concentrations (0.2 and 0.5 mM), enzyme activity declined progressively. Examination of induced recombinant E. coli cells by transmission electron microscopy showed the presence of only periplasmic inclusion bodies at low IPTG concentrations
(up to 0.1 mM) and both periplasmic and cytoplasmic inclusion bodies at high IPTG concentrations (0.2 mM and 0.5 mM). Results
from sodium dodecyl sulfate/polyacrylamide gel electrophoresis and immunoblots of whole-cell proteins, membrane proteins and
inclusion body proteins in these cells indicated that cytoplasmic inclusion bodies constituted an accumulation of preproenzyme
(i.e., precursor polypeptide containing a signal peptide) and that periplasmic inclusion bodies constituted an accumulation
of proenzyme (i.e., precursor polypeptide lacking a signal peptide).
Received: 27 March 1996 / Received revision: 2 July 1996 / Accepted: 10 November 1996 相似文献
17.
A. Brunella M. Graf M. Kittelmann K. Laumen O. Ghisalba 《Applied microbiology and biotechnology》1997,47(5):515-520
Rhodococcus equi Ac6 was found to express an inducible (S )-specific N-acetyl-1-phenylethylamine amidohydrolase. Optimal bacterial growth and amidohydrolase expression were both observed around
pH 6.5. Purification of the enzyme to a single band in a Coomassie-blue-stained sodium dodecyl sulfate/polyacrylamide gel
(SDS-PAGE) was achieved by ammonium sulfate precipitation of R. equi Ac6 crude extract and column chromatographies on Fractogel TSK Butyl-650(S) and Superose 12HR. At pH 7.0 and 30 °C the amidohydrolase
had a half-life of around 350 days; at 44 °C it was only 10 min. Except for Ni2+ and, to some extent, Zn2+ and Co2+, the enzyme was neither strongly influenced by metal cations nor by chelating agents, but was inhibited by 95% at 0.1 mM
phenylmethylsulfonyl fluoride. The molecular mass of the native enzyme was estimated to be 94 kDa by gel filtration and 50 kDa
by SDS-PAGE, suggesting a dimeric structure. Specificity experiments revealed a spectrum of related N-acetylated compounds being hydrolyzed with variable enantiomeric selectivities.
Received: 20 September 1996 / Received revision: 23 December 1996 / Accepted: 30 December 1996 相似文献
18.
K. M. J. Van Laere G. Beldman A. G. J. Voragen 《Applied microbiology and biotechnology》1997,47(3):231-235
An arabinofuranohydrolase (AXH-d3) was purified from a cell-free extract of Bifidobacterium adolescentis DSM 20083. The enzyme had a molecular mass of approximately 100 kDa as determined by gel filtration. It displayed maximum
activity at pH 6 and 30 °C. Using an arabinoxylan-derived oligosaccharide containing double-substituted xylopyranosyl residues
established that the enzyme specifically released terminal arabinofuranosyl residues linked to C-3 of double-substituted xylopyranosyl
residues. In addition, this arabinofuranohydrolase released arabinosyl groups from wheat flour arabinoxylan polymer but showed
no activity towards p-nitrophenyl α-l-arabinofuranoside or towards sugar-beet arabinan, soy arabinogalactan, arabino-oligosaccharides and arabinogalacto-oligosaccharides.
Received: 15 July 1996 / Received revision: 18 October 1996 / Accepted: 18 October 1996 相似文献
19.
The white-rot fungi Trametes versicolor PRL 572, Trametes versicolor MUCL 28407, Pleurotus ostreatus MUCL 29527, Pleurotus sajor-caju MUCL 29757 and Phanerochaete chrysosporium DSM 1556 were investigated for their ability to degrade the polycyclic aromatic hydrocarbons (PAH) anthracene, benz[a]anthracene and dibenz[a,h]anthracene in soil. The fungi were grown on wheat straw and mixed with artificially contaminated soil. The results of this
study show that, in a heterogeneous soil environment, the fungi have different abilities to degrade PAH, with Trametes showing little or no accumulation of dead-end metabolites and Phanerochaete and Pleurotus showing almost complete conversion of anthracene to 9,10-anthracenedione. In contrast to earlier studies, Phanerochaete showed the ability to degrade the accumulated 9,10-anthracenedione while Pleurotus did not. This proves that, in a heterogeneous soil system, the PAH degradation pattern for white-rot fungi can be quite different
from that in a controlled liquid system.
Received: 20 March 1996 / Received revision: 2 July 1996 / Accepted: 8 July 1996 相似文献
20.
Bioremediation of two diesel-oil-contaminated alpine subsoils, differing in soil type and bedrock, was investigated in laboratory
experiments at 10 °C after supplementation with an inorganic fertilizer. Initial diesel oil contamination of 4000 mg kg−1 soil dry matter (dm) was reduced to 380–400 mg kg−1 dm after 155 days of incubation. In both soils, about 30 % of the diesel oil contamination (1200 mg kg−1 dm) was eliminated by abiotic processes. The residual decontamination (60 %–65 %) could be attributed to microbial degradation
activities. In both soils, the addition of a cold-adapted diesel-oil-degrading inoculum enhanced biodegradation rates only
slightly and temporarily. From C/N and N/P ratios (determined by measuring the contents of total hydrocarbons, NH4
+ N, NO3
− N and PO4
3− P) of soils␣it could be deduced that there was no nutrient deficiency during the whole incubation period. Soil biological
activities (basal respiration and dehydrogenase activity) corresponded to the course of biodegradation activities in the soils.
Received: 9 September 1996 / Accepted: 7 December 1996 相似文献