Shuichi Aiba

Kinetics of product inhibition in alcohol fermentation

The inhibitory effect of ethanol concentration p in a medium on the specific rates of growth μ and ethanol production ν of a specific strain of bakers yeast was studied in a chemostat, where except for ethanol as the product, only the concentration of glucose S was controlled to limit the metabolic activity of the yeast. This was designed to supplement the previous findings from the batch experiment, in which ethanol was added artificially and no substrate components were limiting the metabolism of the same yeast, that μ = μ0e  −k 1p and ν = ν0e  −k 2p , where k1 and k2 are empirical constants and subscript the 0 denotes respective values at p = 0. The effects of p on the values of μ and ν were confirmed by the Lineweaver‐Burk plot to belong to noncompetitive inhibition. The formulas here for μ and ν as affected by p, if extrapolated to the case of no limiting substrates, were in good agreement in respective forms with those derived previously from the batch experiment, though the values of corresponding coefficients in these formulas were different. The differential equations for μ and ν as functions of both p and S and, in addition for the rate of glucose consumption as correlated by the yield factors either with the cell growth rate or the rate of ethanol production, were solved properly with a digital computer. A kinetic, pattern calculated so far was discussed with reference to the data obtained in the batch experiment and those relevant to actual “sake” brewing.

Reassessment of Maintenance and Energy Uncoupling in the Growth of Azotobacter vinelandii

SUMMARY: Growth yields of Azotobacter vinelandii from carbon source and oxygen were reassessed to define more clearly the terms, maintenance and true growth yield. In oxygen-limited chemostat cultures, the maintenance coefficients, m (mmol glucose/mg bacteria/h) and m 0 (mmol O2/mg bacteria/h) were 8 × 10-4 and 5.5 × 10-3; i.e. 6m ≃ m 0. This relationship between m and m 0 explains the perfect oxidation of carbohydrate (glucose) by maintenance metabolism. Values of the true growth yield, Y G (mg bacteria/mmol glucose) and Y GO (mg bacteria/mmol O2) were 46 and 13; these values were lower than those recorded for other micro-organisms. In glucose-limited chemostat cultures, fairly high values of m and m 0 were observed and in addition, negative values of Y G and Y GO were obtained. Energy-uncoupled growth could account for these negative values.

Effect of copper and hexavalent chromium on the specific growth rate of ciliata isolated from activated-sludge

Abstract After growing mass and monoxenic cultures of three species of Ciliata ( Vorticella microstoma, Colpidium campylum , and Opercularia sp.) with Alcaligenes faecalis as the sole protozoan food, and confirming that copper and hexavalent chromium did not affect the bacterial growth, the effect of these metals on the specific growth rate of each protozoa was examined. The term IL m (median inhibitory limit) was used to define the metal concentration required to reduce the specific growth rate of protozoa to one-half of that of a control. The IL m for copper was: 0·25 mg 1 −1 ( V. microstoma ), 0·32 mg 1 −1 ( C. campylum ), and 0·27 mg 1 −1 ( Opercularia sp.). Regarding hexavalent chromium, IL m for V. microstoma, C. campylum , and Opercularia sp. were 0·53, 12·9 and 20·2 mg 1 −1 , respectively. Acclimation of each protozoa to these metals for 96 h resulted in IL m enhanced values of 1·2–2·2 times as large as that for the control.

Simulation of PO4;P balance in a shallow and polluted river

Abstract A sophisticated and one-dimensional model to simulate the concentration of PO 4 ;P (x,i) in a shallow and polluted river is presented; the model incorporates, other than the convection and dispersion, various physico-chemical and biochemical reactions of phosphorus sinks and sources. With reference to the field data on Tama-gawa, which penetrates through the metropolitan area of Tokyo, the model is confirmed to represent the concentration of PO 4 ;P fairly well in the mid-region except for the mountainous origin and its estuary. A material balance of PO 4 ;P, the calculation of which is made possible from the model, reveals that about 15% of the daily phosphorus input into the region is fixed by algae on the river bottom, while about 54% of the input flows downstream without being fixed. The balance also discloses that phosphorus decrease due to adsorption on to suspended solid and the increase attributable to hydrolysis of condensed phosphates in the water can be disregarded, respectively. The rest of PO 4 P balance amounting to about 30% is composed of adsorption on to the river-bed, seepage into the groundwater and release from the non-viable algal decomposition. The model is also used to simulate the PO 4 ;P concentration in the region under various conditions. Though naive, the most effective means to decrease the concentration is found, from the model, to be to curtail as much as possible the phosphorus inflow from tributaries.

Significance of the estimation light-absorption rate in the analysis of growth of - Rhodopseudomonas spheroides

SummaryRhodopseudomonas spheroides S was cultured anaerobically and batchwise in light. The light-absorption rate of the cells was assessed by solving numerically an integro-differential equation (Boltzmanns equation) using end Monte Carlo method.For light-limited growth, the specific growth rate of the cells was correlated linearly with the specific light-absorption rate.The Lambert-Beer law could not be used to assess correctly the light absorption by the bacterial cells in the culture medium, because the scattering of light by the cells could not be neglected. The correlation between the light-absorption rate and the cell concentration in the medium is discussed in relation to the scale-up of bio-photoreactors.

Effect of dissolved oxygen on growth yield and aldolase activity in chemostat culture of Azotobacter vinelandii.

SUMMARY: Glucose-limited and oxygen-limited chemostat cultures of Azotobacter vinelandii were agitated at 240, 340, 560 and 780 rev./min. In the oxygen-limited culture the growth yield ranged from 0·2 to 0·25 mg. bacteria/mg. glucose, considerably higher than 0·03 to 0·18 observed when glucose was limiting. This finding suggests that the dissolved oxygen interferes in the metabolism of growing Azotobacter. Aldolase activity, but not that of glyceraldehyde-3-phosphate dehydrogenase, isocitrate dehydrogenase or isocitrate lyase, was proportional to dissolved oxygen concentration in each culture. The carbon balance indicated no products other than the bacteria and carbon dioxide.

Mass and monoxenic culture of vorticella microstoma isolated from activated sludge

Abstract Following previous work on the monoxenic culture of Vorticella microstoma isolated from activated sludge, Sudo and Aiba (1971), a mass culture of the protozoa was attempted. An appropriate range of phosphate buffer concentration in cultivating the protozoa, using sludge bacteria as food, was from 1/150 to 1/75 M, and the optimum pH value of the culture medium ranged from 6·5 to 7·5. For a measurement of dry mass of single cells of Vorticella microstoma, and also for an assessment of some relationship between protozoan growth and bacterial consumption, a pure culture of Alcaligenes faecalis was given as food. The specific growth rate, μ (= 1·5–1·8 day−1) observed with the protozoa was independent of the inoculum size, provided the bacterial concentration was less than 200 mg 1−1 (3·6 × 105 ml−1). The yield on conversion from Alcaligenes faecalis to Vorticella microstoma was 0·47.

Growth rate of aspidiscidae isolated from activated sludge

Abstract Isolation, stock and in addition, monoxenic culture of specific species of Aspidiscidae, Aspidisca costata and Aspidisca lynceus were attempted successfully. Aspidiscidae are the typical protozoa found frequently in the activated sludge from municipal sewage treatment. Using a heterogeneous bacterial population isolated from the activated sludge as the protozoan food, the monoxenic growth rate (logarithmic growth phase) of Aspidiscidae and the effect of temperature on the growth rate were measured. The specific growth rate was 1·2–1·3 day −1 at 20°C, about one-half of that observed with Vorticellidae at the same temperature. Aspidiscidae examined were “stenophagic” and “horozoic”. The optimum temperature for growth was about 30°C and the value of activation energy for growth was ΔE = 13,800 cal mole −1 .

Energetics of Growth of Azotobacter vinelandii in a Glucose-limited Chemostat Culture

SUMMARY: With a glucose-limited chemostat culture of Azotobacter vinelandii iam 1078 the yield factor, Y X/S, for glucose increased from 0·3 to 0·12 following an increase in the dilution rate from 0·1 to 0·35 hr-1. However, even when growing at the faster rate the value of Y X/S still was extremely small compared to those found with other micro-organisms. This low yield value was not due to an incomplete oxidation of glucose, since most of the glucose carbon utilized (83 to 97%) could be accounted for as carbon dioxide, the percentage conversion depending on the dilution rate. The specific respiration rate (Q o2 ) of the growing culture was determined in situ and found to remain nearly constant over the range of dilution rates. However, the value of Y X/S diminished progressively from 0·12 to 0·03 when the dissolved oxygen concentration in a chemostat culture was increased from 3·3 to 5·7 p.p.m. The yield factor, Y ATP (evaluated by making certain assumptions) was much smaller than the value of 10 found with other microbial culture, even though the value of Y ATP increased appreciably with the increase of dilution rate. These results are discussed with reference to some of the known physiological characteristics of A. vinelandii.

ENGINEERS' APPROACH TO THE AUTOMATIC CONTROL OF MICROBIOLOGICAL PROCESSES

This chapter presents an engineers approach to the automatic control of microbiological processes. The automatic control of various factors such as pH, dissolved oxygen, and temperature in the microbiological processes, primarily in the fermentation industry has developed. This is because of the progress observed in sensors and in theories relevant to the automatic control. In this chapter, the feedback principle is discussed from a general standpoint of the automatic control. This kind of feed-back can also be envisaged in the microbial activities of producing a specific material. Lysine accumulation is cited in this context. The transfer function that is underlying the feed-back mechanism and is indispensable for designing any automatic control system is reviewed. A certain similarity between the biological and non-biological systems is referred to. The finding on a dynamical response of microbial activities has discussed and the need for further study along the line has been emphasized before one can proceed to control automatically the activities of any microbes, though the automatic control of environmental conditions such as pH, temperature and so forth is being employed in the fermentation industry.