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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 52 (1999), S. 617-627 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Many attempts have been made for the last six decades to design defined media for species of the lactococcus group. The general outcome of the studies suggests that this group is heterogeneous with respect to specific requirements for nutrients. Lactococcal species are limited in various metabolic pathways. Early attempts to trace the required nutrients were not always successful because of the poor quality of analysis and the presence of impurities in the medium components.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Because biomass is a widely available, renewable resource, its utilisation for the production of energy has great potential for reducing CO2 emissions and thereby preventing global warming. In this mini-review the `state of the art' of several fermentation processes is discussed, starting with the most advanced process of ethanol production. This is followed by methane production, an established process for waste water purification which is gaining more attention because of the inherent energy production. Subsequently ABE fermentation is discussed and finally the biological production of hydrogen. The last section proposes a new way to assess and compare the different processes by relating their merit to `work content' values and `lost work' instead of the combustion values of their products. It is argued that, especially when dealing with energy from biomass, the application of this methodology will provide a uniform valuation for different processes and products. The described fermentation processes enable the supply of pure energy carriers, either gaseous or liquid, from biomass, yet the introduction of these processes is hampered by two major problems. The first is related to technological shortcomings in the mobilisation of fermentable components from the biomass. The second, having a much greater impact, is linked with socio-economics: until full externality costs are attributed to fossil fuels, accounting for their role in pollution and global warming, the competitiveness of the processes described here will hardly stand a chance.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract In acetate-limited chemostat cultures of Acinetobacter johnsonii 210A at a dilution rate of 0.1 h−1 the polyphosphate content of the cells increased from 13% to 24% of the biomass dry weight by glucose (100 mM), which was only oxidized to gluconic acid. At this dilution rate, only about 17% of the energy from glucose oxidation was calculated to be used for polyphosphate synthesis, the remaining 83% being used for biomass formation. Suspensions of non-growing, phosphate-deficient cells had a six- to tenfold increased uptake rate of phosphate and accumulated polyphosphate aerobically up to 53% of the biomass dry weight when supplied with only orthophosphate and Mg2+. The initial polyphosphate synthesis rate was 98 ± 17 nmol phosphate min−1 mg protein−1. Intracellular poly-β-hydroxybutyrate and lipids served as energy sources for the active uptake of phosphate and its subsequent sequestration to polyphosphate. The H+-ATPase inhibitor N,N′-dicyclohexylcarbodiimide caused low ATP levels and a severe inhibition of polyphosphate formation, suggesting the involvement of polyphosphate kinase in polyphosphate synthesis. It is concluded that, in A. johnsonii 210A, (i) polyphosphate is accumulated as the energy supply is in excess of that required for biosynthesis, (ii) not only intracellular poly-β-hydroxybutyrate but also neutral lipids can serve as an energy source for polyphosphate-kinase-mediated polyphosphate formation, (iii) phosphate-deficient cells may accumulate as much polyphosphate as activated sludges and recombinants of Escherichia coli designed for polyphosphate accumulation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Lactococcus lactis ssp. lactis ATCC 19435 is known to produce mixed acids when grown on maltose. A change in fermentation conditions only, elevated temperatures (up to 37 °C) and reduced pH values (down to 5.0) resulted in a shift towards homolactic product formation. This was accompanied by decreased growth rate and cell yield. The results are discussed in terms of redox balance and maintenance, and the regulation of lactate dehydrogenase and pyruvate formate-lyase.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thiosphaera pantotropha is capable of aerobic heterotrophic nitrification and both aerobic and anaerobic denitrification. These phenomena have been studied in acetate-limited aerobic and anaerobic continuous cultures supplied with ammonia and nitrate. The internal reaction rates were defined, based on biochemical knowledge. The observable external conversion rates are related through a linear equation on the basis of the specified internal reaction rates. The linear equation is a Pirt relation extended for microbial systems with multiple electron donors (acetate and ammonia) and electron acceptors (oxygen and nitrate). The coefficients in this equation were estimated from the continuous culture measurements, and are composed of parameters involved in ATP production and consumption by the microorganism. It is shown that with realistic values for these parameters, the metabolically structured model describes the aerobic as well as the anaerobic experiments.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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