摘要:

AbstractThis work concerns mathematical modeling of the rate of microbial growth on inhibitory levels of nutrients as affected by pH, concentration of the nutrients, temperature, cultivation method, and method of data analysis.Candida utilis(ATCC 9226) was grown with sodium acetate as growth‐limiting carbon and energy source in mineral salts medium in shake flask and continuous cultures to study inhibition by excess acetate. Differential shake flask cultures were grown at low yeast concentrations at temperatures (T) of 25 and 30°C, pH's between 5.5 and 7.0, and acetate concentrations (S) between 0.25 and 3.0% (w/v). Growth data were exponential with correlation coefficients greater than 0.995 in 49 of 56 experiments; the lowest correlation coefficient was 0.986. Specific growth rates (μ) determined by graphical methods showed only fair correlation with those determined by regression analysis. Both sets of specific growth rate data were grouped at constantTand pH and fitted to the three parameter equation,\documentclass{article}\pagestyle{empty}\begin{document}$$\mu = \mu _m /(K_s + S + S + S^2 / K_i )$$\end{document}The improvement in use of the fitted equation instead of the mean value was significant with greater than 70% confidence in all (14 groups) and 90% confidence in only half of the data groups; the correlation does not improve with the increasing acetate inhibition at lower pH. Both defects in the model and insufficient data at each pH are responsible. A modified six parameters with hydrogen ion concentration(H+) as follows:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\mu _m = \mu _m /(1 + K_2 /{\rm H}^ + + {\rm H}^ + /K_1 )} \\ {K_i = K_I (1 + {{K_3 } \mathord{\left/ {\vphantom {{K_3 } {{\rm H}^ + }}} \right. \kern-\nulldelimiterspace} {{\rm H}^ + }})} \\ {K_s = {\rm Contant}} \\ \end{array} $$\end{document}Specific growth rates calculated with the six parameter equation matched observed values in all groups of isothermal data better than the means with greater than 99% confidence. The six parameter model adequately represents effects of acetate and hydrogen ion concentrations under constant or slowly changing environmental conditions and balanced growth; although better models probably exist. Thus steady‐stste and transient continuous culture experiments agreed with many published growth yields, but specific growth rates could only be predicted qualitatively from the model fit to the shake flask data. The data and present models could be incorporated into published models for transient growth at low nutrient concentrations to correlate and perhaps predict microbial growth kinetics over a much wider range of growth conditions than now pos

ISSN:0006-3592    

DOI:10.1002/bit.260170702

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

年代:1975

数据来源: WILEY

摘要:

AbstractGrowth and acetate metabolism byCandida utilis(ATCC 9226) is reported for both acetate‐ and zinc‐limited cultures in defined media. Acetate concentrations were varied from suboptimal to inhibitory levels in both types of media in differential shake flask culture and in batch and continuous cultures in stirred fermentors. Transient responses of steady‐state cultures to small or large additions of concentrated sodium acetate, or to shifts in dilution rate or inlet acetate concentration are compared with one another and with simple mathematical models of growth and acetate metabolism. Exponential growth was observed during unrestricted growth (differential shake flask and batch cultures) with both types of media. Addition of acetate during unrestricted growth always caused lags and for larger pulses, lower specific growth rates were observed after exponential growth resumed. Inhibition by high acetate concentrations was much greater in acetate–limited than in zinc–limited cultures. During restricted growth (steady‐state, continuous cultures), high acetate concentrations again consistently caused growth lags but stimulated, inhibited, or temporarily stopped acetage uptake. Qualitative agreement between the predictions of a simple mathematical model of acetate inhibition fitted to differential shake flask data and the observed transient data was surpri

ISSN:0006-3592    

DOI:10.1002/bit.260170703

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

年代:1975

数据来源: WILEY

摘要:

AbstractAn apparatus for the cultivation of microorganism under controlled conditions is described. This apparatus is basically a turbidostat improved with automatic devices for sample withdrawal and tube cleaning. The results of experiments, usingEuglena gracilisto check the constancy of some physiological parameters (in particular phototactic reactivity), are reported.

ISSN:0006-3592    

DOI:10.1002/bit.260170704

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

年代:1975

数据来源: WILEY

摘要:

AbstractA mathematical model was developed to simulate, on a digital computer, the continuous fermentation of whey lactose to lactic acid with neutralization by ammonia. The simulation predicted the retention times for experimental test and the use of two stages for greatest efficiency. In the experimental tests,Lactobacillus bulgaricuswas inoculated into whey in a 14‐liter continuous fermentor at 44°C and with automatic pH control. A series of steady‐state conditions was managed nonaseptically for 42 days without evident contamination and with an actual increase in the efficiency of conversion. Lactic acid was produced predominately' throughout the period, with less than 0.2% of other compounds. The product contained approximately 8 times as much crude protein (N × 6.25) as the original whey. In a single‐stage fermentation at pH 5.5, a retention time of 15 hr resulted in a residual lactose concentration of 0.7%; and little improvement was realized by increasing the retention time. Increasing the pH to 5.8 resulted in a significant improvement, but further increasing the pH to 6.0 resulted in only a small additional gain. By the employment of two fermentors in series at pH 5.5 with a total retention time of 31 hr, the residual lactose was reduced to less than 0.1%. Lactic acid was produced as a function mainly of maintenance rather than growth met

ISSN:0006-3592    

DOI:10.1002/bit.260170705

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

年代:1975

数据来源: WILEY

摘要:

AbstractA microbial protease was immobilized by covalent attachment, to porous glass. This material was characterized for pH optimum, thermal stability, and operational half–life using casein as substrate.The immobilized enzyme was used for preparation of soya hydrolysates, low in free amino acids with high solubilit

ISSN:0006-3592    

DOI:10.1002/bit.260170706

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

年代:1975

数据来源: WILEY

摘要:

AbstractA hollow fiber module was used as a reactor for conversion of ethanol to acetaldehyde in the presence of horse liver alcohol dehydrogenase as catalyst. Mass transport rates for NAD+, the overall acetaldehyde generation rate, catalyst effectiveness factors, and the overall order of the reaction with respect to NAD+concentration were measured. A coupled‐substrate reactor with continuousin situregeneration of cofactor was also examined. Two substrates of opposite redox state were added simultaneously to the feed stream. NADH and acetaldehyde concentrations were monitored in the effluent stream. The cofactor recycle number, or ratio of moles of product to moles of NADH produced, exceeded 10,000 under certain conditions. While decreasing the NAD+concentration in the feed stream decreased reactor productivity somewhat, it greatly enhanced the ratio of product formed per mole of NAD+fed to the reactor. It is suggested that high cofactor costs in dehydrogenase reactors may be overcome with efficientin situregeneration and secondary recovery and recycling of cofactor from the process strea

ISSN:0006-3592    

DOI:10.1002/bit.260170707

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

年代:1975

数据来源: WILEY

摘要:

AbstractRecent findings in the author's laboratories relative to the determination of the mode of response of continuously cultured heterogeneous populations to step changes in pH and in temperature are reviewed and discussed in light of possible effects of specific growth rate, μ, on the severity of substrate leakage in the effluent during the transient phase

ISSN:0006-3592    

DOI:10.1002/bit.260170708

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe dynamics of a system of two microbial populations having complementary metabolism are investigated by means of simple mathematical models of growth. Complementary metabolism as used here means that each population produces a substance—not present in the initial or feed medium—required by the other for growth. The simple models indicate that (1) something other than lack of the substrate or growth factor produced by its partner must limit the growth of at least one population and (2) the coexistence steady state of such populations in continuous culture is not stable with respect to large perturbations, though it is stable with respect to a wide range of perturbati

ISSN:0006-3592    

DOI:10.1002/bit.260170709

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

年代:1975

数据来源: WILEY

摘要:

AbstractValues of the enhancement factor for oxygen absorption into fermentation broth, i.e., the ratio of the liquid phase mass transfer coefficients for oxygen absorption for both cases with and without respiration of microorganisms were predicted theoretically on the assumption of various cell concentration distributions. Calculations indicate that in the usual case the enhancement factor is only slightly or negligibly larger than unity, even when accumulation of microorganisms at or near the gas‐liquid interface is assumed. Results of experiments with sparged‐stirred fermentors on oxygen absorption into fermentation broths containing resting and growing cells ofCandida tropicalisconfirmed the theoretical prediction. Except for extreme cases, the effect of respiration of microorganisms onkLa, values can practically be igno

ISSN:0006-3592    

DOI:10.1002/bit.260170710

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

年代:1975

数据来源: WILEY

ISSN:0006-3592    

DOI:10.1002/bit.260170701

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

年代:1975

数据来源: WILEY