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1.
Summary The use of reticulated polyurethane foam as a support material for the immobilization of methanogenic associations and its application to the anaerobic treatment of fine particulate solid wastes was investigated. The colonization of polyurethane support particles in a continuous upflow reactor fed on a mixture of acetate, propionate and butyrate, was both rapid and dense. The combination of rumen microorganisms and colonized support particles in a two-phase digester resulted in an efficient anaerobic decomposition of papermill sludge. 相似文献
2.
The influence of growth rate, the presence of acetate and variation in the dissolved oxygen concentration on the kinetics
of nitrite oxidation was studied in suspensions of intact cells of Nitrobacter winogradskyi and Nitrobacter hamburgensis. The cells were grown in nitrite-limited chemostats at different dilution rates under chemolithotrophic and mixotrophic conditions.
Growth of N. hamburgensis in continuous culture was dependent on the presence of acetate. Acetate hardly affected the maximal nitrite oxidation rate
per cell (V
max), but displayed a distinctly negative effect on the saturation constants for nitrite oxidation (K
m
) of both Nitrobacter species. This effect was reversible; when acetate was removed from the suspensions the K
m
-values for nitrite oxidation returned to their original values.
A reduction of the dissolved oxygen concentration from 100% to 18% air saturation slightly decreased the V
max of chemolithotrophically grown N. winogradskyi cells, whereas a 2.3 fold increase was observed with mixotrophically grown cells of N. hamburgensis. It is suggested that the large variation in K
m
encountered in field samples could be due to this observed phenotypic variability. The V
max per cell is not a constant, but apparently is dependent on growth rate and environmental conditions. This implies that potential
nitrite oxidation activity and numbers of cells are not necessarily related. Considering their kinetic characteristics, it
is unlikely that N. hamburgensis is able to compete succesfully with N. winogradskyi for limiting amounts of nitrite under mixotrophic conditions. However, at reduced partial oxygen tensions, N. hamburgensis may become the better competitor. 相似文献
3.
W. De Boer P. J. A. Klein Gunnewiek R. A. Kester A. Tietema H. J. Laanbroek 《Plant and Soil》1993,149(2):292-296
The effectiveness of acetylene (C2H2) as inhibitor of nitrification was studied in relation to the decomposition of C2H2. This was done by examining the effects of single and multiple additions of different C2H2 concentrations (10, 100, 1000 Pa) on mineral N and NO3
–-N production in samples of the organic (FH) and upper mineral (Ah) layer of an acid oak-beech forest soil. The decomposition of C2H2 was much faster in Ah samples than in FH samples. A single addition of 10 Pa C2H2 was not sufficient for complete inhibition of nitrification in the Ah samples. Nitrification was blocked completely by all other C2H2 treatments in both FH and Ah samples. Addition of C2H2 decreased net mineral N production in Ah samples but not in FH samples. Addition of carboxymethyl-cellulose and chitin to Ah soil had no affect on the rate of decomposition of C2H2. Chitin had a negative effect on net NO3
–-N production. 相似文献
4.
Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Dual Energy-Limited Chemostats 总被引:17,自引:5,他引:12 下载免费PDF全文
The absence of nitrification in soils rich in organic matter has often been reported. Therefore, competition for limiting amounts of ammonium between the chemolithotrophic ammonium-oxidizing species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis was studied in the presence of Nitrobacter winogradskyi in continuous cultures at dilution rates of 0.004 and 0.01 h−1. Ammonium limitation of A. globiformis was achieved by increasing the glucose concentration in the reservoir stepwise from 0 to 5 mM while maintaining the ammonium concentration at 2 mM. The numbers of N. europaea and N. winogradskyi cells decreased as the numbers of heterotrophic bacteria rose with increasing glucose concentrations for both dilution rates. Critical carbon-to-nitrogen ratios of 11.6 and 9.6 were determined for the dilution rates of 0.004 and 0.01 h−1, respectively. Below these critical values, coexistence of the competing species was found in steady-state situations. Although the numbers were strongly reduced, the nitrifying bacteria were not fully outcompeted by the heterotrophic bacteria above the critical carbon-to-nitrogen ratios. Nitrifying bacteria could probably maintain themselves in the system above the critical carbon-to-nitrogen ratios because they are attached to the glass wall of the culture vessels. The numbers of N. europaea decreased more than did those of N. winogradskyi. This was assumed to be due to heterotrophic growth of the latter species on organic substrates excreted by the heterotrophic bacteria. 相似文献
5.
An anaerobic continuous culture study was made with Campylobacter spec. to determine growth yields under various growth conditions. The growth media contained 0.1% (w/v) yeast extract as carbon source. When grown in an aspartate-limited culture Y
asp
max
was 4.6. Inclusion of formate in the culture medium hardly affected the true growth yield. The number of ATP equivalents generated in the fumaratereductase system was 0.66 and the Y
ATP
max
was 7.0. In the nitrate reduction with formate 1.7 ATP equivalents were generated, and a YNO
3-
max
of 12.2 was observed. The true growth yield obtained with a mixture of lactate and aspartate was lower than that found with aspartate alone. 相似文献
6.
Background
Long-term benefits in animal breeding programs require that increases in genetic merit be balanced with the need to maintain diversity (lost due to inbreeding). This can be achieved by using optimal contribution selection. The availability of high-density DNA marker information enables the incorporation of genomic data into optimal contribution selection but this raises the question about how this information affects the balance between genetic merit and diversity.Methods
The effect of using genomic information in optimal contribution selection was examined based on simulated and real data on dairy bulls. We compared the genetic merit of selected animals at various levels of co-ancestry restrictions when using estimated breeding values based on parent average, genomic or progeny test information. Furthermore, we estimated the proportion of variation in estimated breeding values that is due to within-family differences.Results
Optimal selection on genomic estimated breeding values increased genetic gain. Genetic merit was further increased using genomic rather than pedigree-based measures of co-ancestry under an inbreeding restriction policy. Using genomic instead of pedigree relationships to restrict inbreeding had a significant effect only when the population consisted of many large full-sib families; with a half-sib family structure, no difference was observed. In real data from dairy bulls, optimal contribution selection based on genomic estimated breeding values allowed for additional improvements in genetic merit at low to moderate inbreeding levels. Genomic estimated breeding values were more accurate and showed more within-family variation than parent average breeding values; for genomic estimated breeding values, 30 to 40% of the variation was due to within-family differences. Finally, there was no difference between constraining inbreeding via pedigree or genomic relationships in the real data.Conclusions
The use of genomic estimated breeding values increased genetic gain in optimal contribution selection. Genomic estimated breeding values were more accurate and showed more within-family variation, which led to higher genetic gains for the same restriction on inbreeding. Using genomic relationships to restrict inbreeding provided no additional gain, except in the case of very large full-sib families. 相似文献7.
8.
A. Martijn Antheunisse Roos Loeb Marzia Miletto Leon P. M. Lamers Hendrikus J. Laanbroek Jos T. A. Verhoeven 《Plant and Soil》2007,292(1-2):45-61
In the framework of rehabilitation efforts to enhance the ecological value of closed-off estuaries, we studied the effects
of restoring a tidal movement and seawater incursion on soil nitrogen conversion rates and vegetation response of semi-natural
and agricultural grasslands in an outdoor mesocosm experiment. Intact soil monoliths including vegetation were collected in
June 2004 on two locations on the shores of the Haringvliet lagoon in the south-western part of the Netherlands, which used
to be a well-developed estuary before closure in 1970. For more than 1 year, soil monoliths were continuously subjected to
a full-factorial combination of tidal treatment [stagnant/tidal (0.20 m amplitude)] and water type [(freshwater, oligohaline
(salinity = 3)]. Soil, soil moisture and water nitrogen concentrations were monitored for a year, as well as vegetation response
and nitrogen conversion rates in the soil. As expected, nitrogen mineralization rates were enhanced by the tidal treatment
in comparison with the stagnant treatment. Denitrification rates however, were much less affected by tide and were even lower
in the tidal treatments after 3 months in the agricultural grassland soils, implying that in general, soils were more oxic
in the tidal treatments. Oligohaline treatments had virtually no effect on soil nitrogen conversion rates compared to freshwater
treatments. Vegetation performance, however, was lower under saline conditions, especially in the semi-natural grassland.
No further significant differences in response to the tidal and oligohaline treatments were found between the two soils although
they differed strongly in soil characteristics. We conclude that if the rehabilitation measures in the former Haringvliet
estuary are carried out as planned, drastic changes in soil nitrogen processes and vegetation composition will not occur. 相似文献
9.
Effects of substratum on the diversity and stability of ammonia-oxidizing communities in a constructed wetland used for wastewater treatment 总被引:2,自引:0,他引:2
AIM: To study the relationship between the nature of the substratum and the diversity and stability of the ammonia-oxidizing microbial community in a constructed wetland for the treatment of wastewaters. METHODS AND RESULTS: Samples have been taken the year around from sections of the wetland filled with different substrata. When present, the root zones of the helophyte Phragmites australis were also sampled. The diversity of the ammonia-oxidizing community was established by a coupled PCR-DGGE method based on the 16s rRNA gene. Averaged over the seasons, no large differences in community composition were observed between the different substrata, although the section with zeolite always showed the highest frequencies of bands belonging to ammonia-oxidizing bacteria of the beta-subclass of the Proteobacteria. Only sequences related to the Nitrosospira lineage were detected. Averaged again over the seasons, the section with zeolite was also most constant with respect to the potential ammonia-oxidizing activity. CONCLUSIONS: Although the ammonia-oxidizing communities did not differ significantly between the different sections of the constructed wetland, the characteristics of zeolite were most appropriate to accommodate a stable and active community of ammonia-oxidizing bacteria. The presence of the helophyte had no effect on the diversity and stability of the ammonia-oxidizing community. SIGNIFICANCE AND IMPACT OF THE STUDY: It has been shown that substrata used in constructed wetlands made no distinction between ammonia-oxidizing strains in relation to attachment. However, zeolite had the best performance with respect to activity over the seasons. 相似文献
10.