摘要:

AbstractA cybernetic framework is presented which views microbial response in multiple substrate environments as a judicious investment of cellular resources in synthesizing different key proteins according to an optimal regulatory strategy. A mathematical model is developed within the cybernetic framework for the diauxic growth ofKlebsiella pneumoniaeon a mixture ofD‐glucose andD‐xylose. The “bang–bang” optimal policy describes well the experimental observations obtained using a fermenter coupled to an Apple II microcomputer. Striking variations in respiratory levels are observed experimentally during the switching of the cell's adaptive machinery for the utilization of the less preferred

ISSN:0006-3592    

DOI:10.1002/bit.260270102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractTests to determine the mixing characteristics of the anaerobic downflow stationary fixed film (DSFF) reactor during startup showed that mixing characteristics affected performance. Different mixing profiles were obtained by keeping the same flow distribution system and by varying the number of clay channels (1, 4, and 25) in the DSFF reactors (2–32 L). Results with a clean bed reactor indicated a plug flow pattern with a relatively large extent of dispersion. Recirculation dramatically improved the mixing and the residence time distribution (RTD) changed to that of the completely mixed type. Multiple‐channel reactors exhibited a dead space of ca. 12% of the total volume, likely a result of a less than optimally designed flow distributor. A startup period of 90 days was necessary to achieve a maximum loading rate of between 10 and 15 kg COD/m3day, a volumetric methane production rate of up to 3 m3(STP)/m3day and a COD reduction efficiency of up to 90%. For the first 50 days of operation, the difference in achievable volumetric loading rate and volumetric methane production rate was only related to the surface‐to‐volume ratio of the reactors and was not affected by the number of channels present. After 90 days, the bacterial growth on the support material was sufficient to dramatically increase the amount of dead space in the reactors, especially in multiple‐channel reactors (up to 55% of their volume). As a result, the performance of these reactors deteriorated and overloading characteristics were observed. Other results showed that biogas production alone was not sufficient to improve reactor mixing and that little or no shortcircuiting or channelling occurred. Furthermore, the nonmethanogenic bacterial activity in the liquid phase was not affected by the degree of mixing but acetoclastic methanogenic and hydrogenophilic methanogenic activity in the liquid phase were reduced as the fluid flow pattern in the reactor

ISSN:0006-3592    

DOI:10.1002/bit.260270103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractOptimal conditions for solid substrate fermentation of wheat straw withChaetomium cellulolyticumin laboratory‐scale stationary layer fermenters were developed. The best pretreatment for wheat straw was ammonia freeze explosion, followed by steam treatment, alkali treatment, and simple autoclaving. The optimal fermentation conditions were 80% (w/w) moisture content; incubation temperature of 37°C; 2% (w/w) unwashed mycelial inoculum; aeration at 0.12 L/h/g; substrate thickness of 1 to 2 cm; and duration of three days. Technical parameters for this optimized fermentation were: degree of substance utilization, 27.2%; protein yield/substrate, 0.09 g; biomass yield/bioconverted substrate, 0.40 g; degree of bioconversion of total available sugars in the substrate, 60.5%; specific efficiency of bioconversion, 70.8%; and overall efficiency of biomass production from substrate, 42.7%. Mixed culturing ofCandida utilisfurther increased biomass production by 20%. The best mode of fermentation was a semicontinuous fed‐batch fermentation where one‐half of the fermented material was removed at three‐day intervals and replaced by fresh substrate. In this mode, protein production was 20% higher than in batch mode, protein productivity was maintained over 12 days, and sporulation was p

ISSN:0006-3592    

DOI:10.1002/bit.260270104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractDerepression of the phage λpLpromoter on recombinant plasmid pPLc 23‐trpAlcaused a rapid increase of plasmid free segregants in the population. In continuous culture, increased production oftrpAprotein follwing derepression was accompanied by a continuous deceleration of specific growth rate. In the repressed condition, plasmid loss per generation in continuous culture decreased as dilution rate increased from 0.06 to 1.08 h−1. Over this range, the concentration of plasmid DNA within the cell decreased eightfold corresponding to a decrease in plasmid number from 74 to 32 molecules/cell. The use of a two‐stage continuous culture system coupled with a temperature sensitive expression system allows a hightrpAproductivity from the derepressed plasmid for more than 48 h and also offers a possibility of minimizing the instability problem of high expression recombinants. Such a system also permits the critical study of the effects of fermentation and other regulatory parameters on expression under better controlled conditions than is possible in a batch culture or single‐stage continous

ISSN:0006-3592    

DOI:10.1002/bit.260270105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractSolid‐state fermentation of chopped sweet sorghum particles to ethanol was studied in static flasks using an ethanol tolerant yeast strain. The influence of various process parameters, such as temperature, yeast cell concentration, and moisture content, on the rate and extent of ethanol fermentation was investigated. Optimal values of these parameters were found to be 35°C, 7 × 108cells/g raw sorghum, and 70% moisture level, respectiv

ISSN:0006-3592    

DOI:10.1002/bit.260270106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractMore than 90% of initial pyritic sulfur was removed from bituminous coal samples (containing 2.1% pyritic sulfur) using the thermophilic organismSulfolobus acidocaldarius. Microbial desulfurization rate was improved nearly ten fold by adjusting the N/P and N/Mg ratios in the nutrient medium. Environmental conditions were optimized. The optimal values of temperature and pH were 70°C and 1.5, respectively. The influence of certain process variables (such as coal pulp density, particle size, and initial cell number density) on the rate of pyritic sulfur removal were determined. A pulp density of 20%, particle size ofD¯p<48 μm, and an initial cell number density of 1012cells/g pyrite in coal were found to be optimal. The carbon dioxide enriched air did not improve the rate of pyritic sulfur removal compared to pure air at 10% pulp density of coal samples containing 2.1% pyritic sulfur. The kinetics of microbial leaching of pyritic sulfur from coal was investigated. The rate of leaching was found to be first order with respect to pyritic sulfur concentration in the reaction medi

ISSN:0006-3592    

DOI:10.1002/bit.260270107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractUsing the available information of fermentation biochemistry, fermentation (stoichiometric) equations are derived for anaerobic saccharolytic fermentations of butanediol and mixed acids. The equations describe the interrelations among the fermentation products, biomass, and consumed substrate (glucose). The validity of the equations is tested using a variety of batch data from the literature. The validity of the equations is expected to extend to steady‐state and transient fermentations, as well. Uses, improvements, and extensions of the equations are also discussed in detail. Among others, it is shown that the equations are useful for checking the consistency of experimental data, for calculating maximal yields and selectivities for the fermentation products, and calculating the extent of utilization of the Embden–Meyerhof–Parnas pathway versus the Hexose Monophosphate pathway of glucose utiliz

ISSN:0006-3592    

DOI:10.1002/bit.260270108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractFermentation (stoichiometric) equations are derived for anaerobic fermentations of propionic‐acid bacteria (of both thePropionibacteriumand acrylate pathways) and for production of various oxychemicals (butanol, acetone, isopropanol, butanediol, butyrate, acetate, propionate, succinate, lactate, and acrylate) from pentoses, hexoses, and cellobiose. The derivations of the equations are based on the fermentation biochemistries of the various bacterial classes. The validity of the equations is tested using fermentation data from the literature. The equations are shown to be valuable, among other uses, for calculating maximal yields and selectivities of the various fermentation products, as “gateway sensors” for monitoring of the fermentations, and for calculating the extents of the various intracellular reactions of the fermentation biochem

ISSN:0006-3592    

DOI:10.1002/bit.260270109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractClearing of agar plates containing ball‐milled, delignified straw has been used for screening mutants ofPenicillium funiculosumIMI 87160 iii. The effects of glycerol and a number of sugars on the clearing were investigated for selecting derepressed mutants. The β‐glucosidase synthesis by one such mutant, C22c, in shake flasks containing straw was not repressed by 5% glycerol, whereas activities on filter paper, CM‐cellulose, andp‐nitrophenyl‐β‐xylosidase were only partially derepressed; xylanase was extensively derepressed. The evidence for separate control of the enzymes involved in the solubilization of straw

ISSN:0006-3592    

DOI:10.1002/bit.260270110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe stability of downflow stationary fixed‐film (DSFF) reactors was evaluated under extreme organic shock loads. Reactors could handle five‐ to sevenfold increases in organic loading and recover to normal performance in a relatively short period of time (usually 24–72 h) during treatment of well‐buffered sucrose and acetic acid wastewater at 27 and 35°C. Overloading was characterized by elevated volatile‐acid concentrations, decreased reactor pH, and excess biofilm sloughing. Reactors could not cope with extreme organic shocks during treatment of poorly buffered sucrose wastewater. The pH of the mixed liquor was observed to be a more important factor than the volatile‐acid concentration in determining whether DSFF reactors would recover in a reasonable pe

ISSN:0006-3592    

DOI:10.1002/bit.260270111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY