2149 research outputs found
Sort by
Biomass relationship to growth and phosphate uptake of pseudomonas fluorescens, escherichia coil and acinetobacter radioresistens in mixed liquor medium.
No full textThe ability of Pseudomonas fluorescens, Escherichia coil and Acinetobacter radioresistens to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (102-10 s cells m1-1) were used. At a high initial biomass concentration (108 cells ml 1), phosphate was removed during the lag phase and during logarithmic growth by P. fluorescens. Escherichia coil, at high initial biomass concentrations (107 cells ml-1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantity of phosphate during the stationary growth phase. Acinetobacter radioresistens, at high initial cell densities (106, 10 z cells ml -~) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase. Pseudomonas fluorescens removed phosphate more than A. radioresistens and Eo coil with specific average ranges from 3.00-28.50 mg L .~ compared to average ranges of 4.92-17.14 mg L -1 for A. radioresistens and to average ranges of 0.50-8.50 mg L -~ for E. coil
The relationship of biomass to phosphate uptake by Acinetobacter junii in activated sludge mixed liquor.
No full textThe involvement of Acinetobacter in biological excess phosphate removal from the activated sludge process is widely accepted, though its role is not yet clearly defined. To better understand why activated sludge systems remove phosphate, different cell concentrations of Acinetobacter junii (104, 105, 106, 107, 108 cells·ml−1 initial biomass) were used as inoculum in a mixed liquor medium containing sodium acetate. The phosphate uptake capacity was dependent on the biomass concentration. Low initial biomass concentrations triggered the release of phosphate once transferred into the mixed liquor. Release of phosphate increased during active growth and uptake occurred when cells reached the stationary growth phase. High initial biomass concentration of Acinetobacter junii (108 cells·ml−1) resulted in uptake of phosphate during the entire duration of the experiment leading eventually to complete phosphate removal
Alfalfa (Medicago sativa L) root exudates contain of isoflavonoids in the presence of rhizobium meliloti.
No full textRoot exudates of alfalfa (Medicago sativa 1.) inoculated with symbiotic Rhizobium meliloti bacteria contained three isoflavonoids that were not found in exudates of uninoculated plants. Data from proton nuclear magnetic resonance, mass spectrometry, and ultraviolet-visible absorbance analyses indicated that root exudates of inoculated plants contained aglycone and glycoside forms of the phytoalexin medicarpin and a formononetin-7-0-(6”-0-malonyl glycoside), a conjugated form of the medicarpin precursor formononetin. lhe medicarpin molecules did not induce nod gene transcription in R. meliloti, but the formononetin-7-0-(6”-O-malonylglycoside) induced nod genes regulated by both NodDl and NodD2 proteins in R. meliloti. Hydrolysis of either the malonyl or the glycosyl linkage from the formononetin conjugate eliminated nod gene-inducing activity. lhe nod gene-inducing activity of crude root exudates was increased 200 and 65% upon inoculation with R. meliloti or R. leguminosarum bv phaseoli, respectively. When root exudate from uninoculated alfalfa was incubated with R. meliloti, high performance liquid chromatography analyses showed no evidence that bacterial metabolism produced medicarpin. These results indicate that alfalfa responds to symbiotic R. meliloti by exuding a phytoalexin normally elicited by pathogens and that the microsymbiont can use a precursor of the phytoalexin as a signal
for inducing symbiotic nod genes
The phytosociology of the Villiers - Grootvlei area, South Africa: The plant communities of the Ba Land Type.
No full textThe vegetation of the Ba Land Type is classified by means of TWINSPAN and refined by the Braun-Blanquet method, in nine plant communities. One of the communities is divided into two SUb-communities. The plant communities were related to specific environmental conditions that were confirmed by the ordination (DECORANA) of the data
The phytosociology of the Villiers - Grootvlei area, South Africa: The plant communities of the Ea land type.
No full textThe vegetation of the Ea Land Type in the Villiers - Grootvlei area was classified by means of Braun-Blanquet procedures. A total of 77 releves in the land type were used. On the high-lying areas two major plant communities were encountered, one of which was divided into two sub-communities. On the low-lying areas five major plant communities were recorded, one of which was divided into five sub-communities and another into two sub-communities. A DECORANA ordination confirmed that the communities are related to specific environmental conditions
Isolation of rhizobium meliloti nod gene inducers from alfalfa rhizosphere soil.
No full textMethanolic extracts of alfalfa rhizosphere soil induce more nod gene transcription in Rhizobium meliloti than extracts of nonrhizosphere soil. Six peaks of nod-inducing activity were separated by high-performance liquid chromatography from rhizosphere soil extract, and one compound was identified by 'H nuclear magnetic resonance, mass spectrometry, and UV-visible spectra as a formononetin-7-O-glycoside that activates both NodDl and NodD2 proteins. The unanticipated presence of a glycoside in rhizosphere soil suggests either that large amounts of the glycoside were exuded by roots or that some glycosides are unexpectedly stable in soil
Adaptation of nodulated soybean (Glycine max L. Merr.) to growth in rhizospheres containing nonambient p021.
No full textNodulated soybean (Glycine max L. Merr. cv White Eye inoculated with BradyrhizobiumJaponicum strain CB 1809) plants were cultured in the absence of combined N from 8 to 28 days with their root systems maintained continuously in 1, 2.5, 5, 10, 20, 40, 60, or 80% 02 (volume/volume) in N2. Plant dry matter yield was unaffected by partial pressure of oxygen (PO2) and N2 fixation showed a broad plateau of maximum activity from 2.5 to 40 or 60% 02. Slight inhibition of nitrogenase activity occurred at 1% 02 and as much as 50% inhibition occurred at 80% 02. Low PO2 (less than 10%) decreased nodule mass on plants, but this was compensated for by those nodules having higher specific nitrogenase activities. Synthesis and export of ureides in xylem was maintained at a high level (70-95% of total soluble N in exudate) over the range of PO2 used. Measurements of nitrogenase (EC 1.7.99.2) activity by acetylene reduction indicated that adaptation of nodules to low P02 was largely due to changes in ventilation characteristics and involved increased permeability to gases in those grown in subambient PO2 and decreased permeability in those from plants cultured with their roots in P02 greater than
ambient. A range of structural alterations in nodules resulting from low PO2 were identified. These included increased frequency of lenticels, decreased nodule size, increased volume of cortex relative to the infected central tissue of the nodule, as well as changes in the size and frequency of extracellular voids in all tissues. In nodules grown in air, the inner cortex differentiated a layer of four or five cells which formed a band, 40 to 50 micrometers thick, lacking extracellular voids. This was reduced in nodules grown in low P02 comprising one or two cell layers and being 10 to 20 micrometers thick in those from 1% 02. Long-term adaptation to different external PO2 involved changes which modify diffusive resistance and are additional to adjustments in the variable diffusion barrier
Effect of pO2 on the formation and status of leghemoglobin in nodules of cowpea and soybean.
No full textNodulated cowpea (Vigna unguiculata [L.] Walp. cv Vita 3: Bradyrhizobium strain CB756) and soybean (Glycine max [L.] Merr. cv White Eye: Bradyrhizobium strain CB1809) were grown with their root systems maintained in a flowing gas stream containing a range of P02 (1-80%, v/v) in N2 for up to 28 days after planting. At the extremes of sub- and supra-ambient P02, the levels of leghemoglobin (Lb) in nodules were reduced. However, neither the proportional composition of Lb component proteins (eight in soybean, three in cowpea) nor their oxidation state was affected by PO2. Short-term changes in P02 (transferring plants grown with sub- or supra-ambient PO2 in the rhizosphere to air or vice versa) caused a significant decline in Lb content and, in cowpea but not soybean, where P02 was increased, a higher percentage of oxidation of Lb. Combining data on changes in Lb level of cowpea nodules grown in sub-ambient PO2 with those for their structural adaptation to an under supply of 02 indicated that, despite the nodules having a lower level of Lb, the amount per infected cell was increased by up to twofold and per bacteroid up to fivefold (in those from 1% 02) compared to those grown in air. Progressive decline in P02 resulted in a progressive increase on this basis, indicating a close relationship between Lb content and the adaptation of nodule functioning to external 02 level
Effect of PO2 during growth on the gaseous diffusional properties of nodules of cowpea (Vigna unguiculata L. Walp.)
No full textAdaptations of nodules of cowpea (Vigna unguiculata L. Walp. cv Vita 3: Bradyrhizobium CB 756) to growth in PO2 ranging from 1 to 80% 02 (volume/volume) involved both readily reversible mechanisms of adjustment and more stable alterations which together resulted in nodules with widely ranging resistance to diffusion of gases. Those grown in subambient PO2 (1-5% 02 were altered such that rapid diffusional adjustment was unable to prevent irreversible loss of nitrogenase on their transfer to higher levels of O2. Those cultured in 80% had adapted to over supply of 02 such that their transfer to lower levels of 02 limited both nitrogenase and respiratory CO2 release. There was also some evidence for 'protective respiration.' Measurement of diffusional properties based on gas exchange kinetics indicated that gaseous permeability values for nodules from 5 to 40% 02 were relatively constant around 20 x 10-3 millimeters per second,
while those for nodules from 1% 02 were as high as 67.7 x 10-3 millimeter per second and from 80% as low as 6.8 x 10-3 milli meters per second. Estimates of the thickness of the diffusion barrier ranged from 7.5 micrometers for nodules from 1% 02 to 71.9 micrometers in those from 80% 02