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1.
High-cell-density cultivation of microorganisms 总被引:29,自引:0,他引:29
High-cell-density cultivation (HCDC) is required to improve microbial biomass and product formation substantially. An overview
of HCDC is given for microorganisms including bacteria, archae and eukarya (yeasts). Problems encountered by HCDC and their
possible solutions are discussed. Improvements of strains, different types of bioreactors and cultivation strategies for successful
HCDC are described. Stirred-tank reactors with and without cell retention, a dialysis-membrane reactor, a gas-lift reactor
and a membrane cyclone reactor used for HCDC are outlined. Recently modified traditional feeding strategies and new ones are
included, in particular those for unlimited growth to very dense cultures. Emphasis is placed on robust fermentation control
because of the growing industrial interest in this field. Therefore, developments in the application of multivariate statistical
control, artificial neural networks, fuzzy control and knowledge-based supervision (expert systems) are summarized. Recent
advances using Escherichia coli– the pioneer organism for HCDC – are outlined.
Received: 20 October 1998 / Received revision: 18 December 1998 / Accepted: 21 December 1998 相似文献
2.
Pollutant degradation in biotrickling filters for waste air treatment is generally thought to occur only in the biofilm.
In two experiments with toluene degrading biotrickling filters, we show that suspended microorganisms in the recycle liquid
may substantially contribute to the overall pollutant removal. Two days after reactor start up, the overall toluene elimination
capacity reached a maximum of 125 g m−3 h−1, which was twice that found during prolonged operation. High biodegradation activity in the recycle liquid fully accounted
for this short-term peak of pollutant elimination. During steady-state operation, the toluene degradation in the recycle liquid
was 21% of the overall elimination capacity, although the amount of suspended biomass was only 1% of the amount of immobilized
biomass. The results suggest that biotrickling filter performance may be improved by selecting operating conditions allowing
for the development of an actively growing suspended culture.
Received: 16 June 1999 / Received revision: 17 November 1999 / Accepted: 15 December 1999 相似文献
3.
Bioremediation of pentachlorophenol-contaminated soil by bioaugmentation using activated soil 总被引:11,自引:0,他引:11
C. Barbeau L. Deschênes D. Karamanev Y. Comeau R. Samson 《Applied microbiology and biotechnology》1997,48(6):745-752
The use of an indigenous microbial consortium, pollutant-acclimated and attached to soil particles (activated soil), was
studied as a bioaugmentation method for the aerobic biodegradation of pentachlorophenol (PCP) in a contaminated soil. A 125-l
completely mixed soil slurry (10% soil) bioreactor was used to produce the activated soil biomass. Results showed that the
bioreactor was very effective in producing a PCP-acclimated biomass. Within 30 days, PCP-degrading bacteria increased from
105 cfu/g to 108 cfu/g soil. Mineralization of the PCP added to the reactor was demonstrated by chloride accumulation in solution. The soil-attached
consortium produced in the reactor was inhibited by PCP concentrations exceeding 250 mg/l. This high level of tolerance was
attributed to the beneficial effect of the soil particles. Once produced, the activated soil biomass remained active for 5
weeks at 20 °C and for up to 3 months when kept at 4 °C. The activated attached soil biomass produced in the completely mixed
soil slurry bioreactor, as well as a PCP-acclimated flocculent biomass obtained from an air-lift immobilized-soil bioreactor,
were used to stimulate the bioremediation of a PCP-impacted sandy soil, which had no indigenous PCP-degrading microorganisms.
Bioaugmentation of this soil by the acclimated biomass resulted in a 99% reduction (from 400 mg/kg to 5 mg/kg in 130 days)
in PCP concentration. The PCP degradation rates obtained with the activated soil biomass, produced either as a biomass attached
to soil particles or as a flocculent biomass, were similar.
Received: 31 March 1997 / Received revision: 22 July 1997 / Accepted: 25 August 1997 相似文献
4.
The ability of a photobioreactor to fix CO2 was evaluated with the thermophilic cyanobacterium, Synechocystis aquatilis SI-2. The reactor consisted of three to five flat plates of transparent acrylic plastic standing upright and in parallel
and giving a 0.015-m light path. The reactor was 0.8 m high and 1 m long with 9 l working volume. The effects of the orientation
of the vertical bioreactor, distance between the plates, and culture temperature on the productivity of biomass were investigated
during the summer of 1998 in Kamaishi (39°N, 142°E), Japan. When the illuminated surface reactor was placed in an east–west-facing
orientation, the biomass productivity was roughly 1.4-fold higher than that obtained in a north–south-facing orientation,
because the former received more solar energy than the latter. The productivity based on the overall land area was the same
for plates set either 0.25 m or 0.5 m apart. However, the volumetric productivity of the reactor in which the plates were
set 0.25 m apart was lower than that when the plates were set 0.5 m apart, since the former plates received relatively lower
solar irradiation because of severe mutual shading. When the culture temperature was maintained in its optimal range (37–43 °C),
the productivity was 50% greater than that obtained in a culture at ambient temperature (20–44 °C). The biomass productivity
and CO2 fixation rate were investigated under various experimental conditions. The maximum rate of 53 g CO2 m−2 day−1 was achieved in the temperature-regulated culture with the reactor set in an east–west-facing orientation, the distance between
plates being 0.25 m.
Received: 6 may 1999 / Received revision: 14 June 1999 / Accepted 5 July 1999 相似文献
5.
J. Benitez J. Beltran-Heredia J. Torregrosa J. L. Acero V. Cercas 《Applied microbiology and biotechnology》1997,47(2):185-188
The degradation of olive mill wastewater by aerobic microorganisms has been investigated in a batch reactor, by conducting
experiments where the initial concentration of organic matter, quantified by the chemical oxygen demand, and the initial biomass
were varied. The evolution of the chemical oxygen demand, biomass and the total contents of phenolic and aromatic compounds
were followed through each experiment. According to the Contois model, a kinetic expression for the substrate utilization
rate is derived, and its biokinetic constants are evaluated. This final predicted equation agrees well with all the experimental
data.
Received: 12 June 1996 / Received revision: 11 September 1996 / Accepted: 13 September 1996 相似文献
6.
E. Kostyál M. Borsányi L. Rigottier-Gois M. S. Salkinoja-Salonen 《Applied microbiology and biotechnology》1998,50(5):612-622
The dechlorinating and genotoxicity-removing activities of nitrifying fluidized-bed reactor biomass towards chlorinated organic
compounds in water were shown at level below 1 ppm. The removal rates of adsorbable organic halogens were 200 μg Cl (g VS
day)−1 for chlorinated humic ground water and 50 μyg Cl (g VS day)−1 for chlorinated lake water when studied in batch mode. In a sequenced batch mode the removal rates μg Cl (g VS day)−1] were 2000 from chlorohumus, 1400–1800 from chlorophenols in chlorinated ground water, and 430–720 from chlorohumus in chlorinated
lake water. Genotoxicity was removed to a large extent (60%–80%) from the chlorinated waters upon incubation with nitrifying
reactor biomass. 2,6-Di-, 2,4,6-tri and 2,3,4,6-tetrachlorophenols competed with chlorinated water organohalogens for dechlorination.
The dechlorination of chlorophenols and chlorohumus required no ammonia and was not prevented by inhibitors of ammonia oxidation,
nitrapyrin, parathion, sodium diethyldithiocarbamate, or allylthiourea. Electron microscopical inspection of the biomass showed
the dominance of clusters of bacteria resembling known nitrifying species, Nitrosomonas, Nitrobacter, and Nitrosospira. This was supported by polymerase chain reaction amplification of the biomass DNA with four different primers, revealing
the presence of 16S rDNA sequences assignable to the same species. The most intensive band obtained with the Nitroso4E primer
was shown to be closely related to Nitrosomonas europaea by restriction analysis.
Received: 27 March 1998 / Received revision: 30 July 1998 / Accepted: 31 July 1998 相似文献
7.
J. H. de Best A. Hage H. J. Doddema D. B. Janssen W. Harder 《Applied microbiology and biotechnology》1999,51(2):277-283
A methanogenic mixed population in a packed-bed reactor completely transformed 1,1,1-trichloroethane (10 μM) to chloroethane
by a cometabolic process. Chloroethane was not further transformed. Acetate and methanol served as electron donors. Complete
transformation of 1,1,1-trichloroethane to chloroethane only occurred when sufficient electron donor was fed into the reactor.
Otherwise, besides chloroethane, 1,1-dichloroethane was also found as a product. The products of 1,1,1-trichloroethane transformation
also depended on the type of electron donor present. With acetate, the degree of dechlorination was higher, i.e. more 1,1,1-trichloroethane
was transformed to chloroethane than with methanol. In an enrichment culture obtained from the reactor contents, 1,1,1-trichloroethane
was only transformed to 1,1-dichloroethane and was not further metabolized. Methanol, acetate, formate, ethanol, 2-propanol,
trimethylamine and H2, but not dimethylamine and methylamine, served as electron donors for 1,1,1-trichloroethane transformation by this enrichment
culture. Both nitrate and nitrite inhibited 1,1,1-trichloroethane transformation; while nitrate completely inhibited 1,1,1-trichloroethane
dechlorination, some conversion did occur in the presence of nitrite. The product(s) of this conversion remain unknown, since
no chlorinated hydrocarbons were detected.
Received: 19 June 1998 / Received revision: 14 September 1998 / Accepted: 17 September 1998 相似文献
8.
Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies 总被引:16,自引:0,他引:16
The isotope enrichment ɛ* of 13C between tooth enamel of large ruminant mammals and their diet is 14.1 ± 0.5‰. This value was obtained by analyzing both
the dental enamel of a variety of wild and captive mammals and the vegetation that comprised their foodstuffs. This isotope
enrichment factor applies to a wide variety of ruminant mammals. Non-ruminant ungulates have a similar isotope enrichment,
although our data cannot determine if it is significantly different. We also found a 13C isotope enrichment ɛ* of 3.1 ± 0.7‰ for horn relative to diet, and 11.1 ± 0.8‰ for enamel relative to horn for ruminant
mammals. Tooth enamel is a faithful recorder of diet. Its isotopic composition can be used to track changes in the isotopic
composition of the atmosphere, determine the fraction of C3 or C4 biomass in diets of modern or fossil mammals, distinguish between mammals using different subpathways of C4 photosynthesis,and identify those mammals whose diet is derived from closed-canopy habitats.
Received: 1 July 1998 / Accepted: 9 February 1999 相似文献
9.
Dialysis cultures 总被引:8,自引:0,他引:8
Dialysis techniques are discussed as a means for effective removal of low-molecular-mass components from fermentation broth
to reach high cell density. Reactor systems and process strategies, the relevant properties of membranes and examples for
high-density fermentation with dialysis, and problems related to scale-up are addressed. The dialysis technique has turned
out to be very efficient and reliable for obtaining high cell densities. As in dialysis processes the membranes are not perfused,
membrane clogging is not a problem as it is for micro- and ultrafiltration. By applying a “nutrient-split” feeding strategy,
the loss of nutrients can be avoided and the medium is used very efficiently. The potential of dialysis cultures is demonstrated
on the laboratory scale in a membrane dialysis reactor with an integrated membrane and in reactor systems with an external
dialysis loop. In dialysis cultures with different microorganisms (Staphylococci, Escherichia coli, extremophilic microorganisms, Lactobacilli) the cell densities achieved were up to 30 times higher than those of other fermentation methods. The technique enables high
cell densities to be attained without time-consuming medium optimization. For animal cell cultures the concept of a fixed
bed coupled with dialysis proved to be very effective.
Received: 24 March 1998 / Received revision: 18 June 1998 / Accepted: 19 June 1998 相似文献
10.
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