Influence of agitation and aeration on growth and antibiotic production by <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

The effect of agitation and aeration on the growth and antibiotic production by Xenorhabdus nematophila YL001 grown in batch cultures were investigated. Efficiency of aeration and agitation was evaluated through the oxygen mass transfer coefficient (K _L a). With increase in K _L a, the biomass and antibiotic activity increased. Activity units of antibiotic and dry cell weight were increased to 232 U ml⁻¹ and 19.58 g l⁻¹, respectively, productivity in cell and antibiotic was up more than 30% when K _L a increased from 115.9 h⁻¹ to 185.7 h⁻¹. During the exponential growth phase, DO concentration was zero, the oxygen supply was not sufficient. So, based on process analysis, a three-stage oxygen supply control strategy was used to improved the DO concentration above 30% by controlling the agitation speed and aeration rate. The dry cell weight and activity units of antibiotic were further increased to 24.22 g l⁻¹ and 249 U ml⁻¹, and were improved by 24.0% and 7.0%, compared with fermentation at a constant agitation speed and a constant aeration rate (300 rev min⁻¹, 2.5 l min⁻¹).     

Combined effects of zinc and algal food on the competition between planktonic rotifers, <Emphasis Type="Italic">Anuraeopsis fissa</Emphasis> and <Emphasis Type="Italic">Brachionus rubens</Emphasis> (Rotifera)

We evaluated the combined effects of algal (Chlorella vulgaris) food levels (low, 0.5 × 10⁶ (or 2.9 μg C ml⁻¹); and high, 1 × 10⁶ cells ml⁻¹ (or 5.8 μg C ml⁻¹)) and zinc concentrations (0, 0.125, and 0.250 mg l⁻¹ of ZnCl₂) on the competition between two common planktonic rotifers Anuraeopsis fissa and Brachionus rubens using their population growth. Median lethal concentration data (LC₅₀) (mean ± 95% confidence intervals) showed that B. rubens was more resistant to zinc (0.554 ± 0.08 mg l⁻¹) than A. fissa (0.315 ± 0.07 mg l⁻¹). A. fissa when grown alone or with Zn was always numerically more abundant than B. rubens. When grown in the absence of zinc, under low- and high-food levels, the peak abundances of A. fissa varied from 251 ± 24 to 661 ± 77 ind. ml⁻¹, respectively, and the corresponding maxima for B. rubens were 52 ± 3 and 102 ± 18 ind. ml⁻¹. At a given food level, competition for food reduced the peak abundances of both rotifers considerably. Increase in Zn concentration also lowered the rotifer abundances. The impact of zinc on competition between the two-rotifer species was evident at low-food level, mainly for A. fissa. At zinc concentrations of 0 and 0.125 mg l⁻¹, the populations of both rotifers continued to grow for about 10 days, but thereafter B. rubens began to decline. Role of zinc on the competitive outcome of the two species is discussed in relation to the changing algal densities in natural water bodies.     

Effect of growth rate on the production of<Emphasis Type="SmallCaps">l</Emphasis>-proline in the fed-batch culture of<Emphasis Type="Italic">Corynebacterium acetoacidophilum</Emphasis>

Corynebacterium acetoacidophilum RYU3161 was cultivated in al-histidine-limited fed-batch culture. To investigate the effect of cell growth on thel-proline production, 5l fed-batch culture was performed using an exponential feeding rate to obtain the specific growth rates (μ) of 0.04, 0.06, 0.08, and 0.1 h⁻¹. The results show that the highest production ofl-proline was obtained at μ=0.04 h⁻¹. The specificl-proline production rate (Q_p) increased proportionally as a function of the specific growth rate, but decreased after it revealed the maximum value at μ=0.08 h⁻¹. Thus, the highest productivity ofl-proline was 1.66 g L⁻¹ h⁻¹ at μ=0.08 h⁻¹. The results show that the production of L-proline inC. acetoacidophilum RYU3161 has mixed growth-associated characteristics.     

Competitive inhibition by substrates of the esterification reaction between l-phenylalanine and d-glucose catalysed by the lipases of Rhizomucor miehei and Candida rugosa

A kinetic study on esterification between d-glucose and l-phenylalanine catalysed by lipases from Rhizomucor miehei (RML) and Candida rugosa (CRL) in organic media investigated in detail showed that both the lipases followed a Ping-Pong Bi-Bi mechanism with two distinct types of competitive inhibitions. Graphical double reciprocal plots and computer simulation studies showed that competitive double substrate inhibition took place at higher concentrations leading to dead-end inhibition in the case of RML and in the case of CRL, inhibition only by d-glucose at higher concentrations leading to dead-end lipase–d-glucose complexes. An attempt to obtain the best fit of these kinetic models through curve-fitting yielded in good approximation, the apparent values of important kinetic parameters, RML: k _cat = 2.24 ± 0.23 mM h⁻¹ (mg protein)⁻¹, K _{m l-phenylalanine} = 95.6 ± 9.7 mM, K _{m d-glucose} = 80.0 ± 8.5 mM, K _{i l-phenylalanine} = 90.0 ± 9.2 mM, K _{i d-glucose} = 13.6 ± 1.42 mM; CRL: k _cat = 0.51 ± 0.06 mM h⁻¹ (mg protein)⁻¹, K _{m l-phenylalanine} = 10.0 ± 0.98 mM, K _{m d-glucose} = 6.0 ± 0.64 mM, K _{i d-glucose} = 8.5 ± 0.81 mM.     

Optimization of dilution rate for the production of value added product and simultaneous reduction of organic load from pineapple cannery waste

Candida utiilis NRRL Y-900 was grown on pineapple cannery waste as the sole carbon and energy source in a chemostat at dilution rates ranging between 0.05 and 0.65 h⁻¹ to determine the growth kinetics. The cell yield coefficient varied with dilution rate and a maximum value of 0.662 ± 0.002 g_x/g_carb was obtained at a dilution rate of 0.4 h⁻¹. At steady state, the concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod kinetics. At maximum specific growth rate (μ_max) 0.65 h⁻¹, the saturation constants for carbohydrate, reducing sugar and COD were 0.51 ± 0.02 g_carb/1, 0.046 ± 0.003 g_rs/1, and 1.036 ± 0.001 g_COD/1, respectively. Maximum biomass productivity (Q _{x max}) 2.8 ± 0.03 g_x/1 h was obtained at a dilution rate of 0.5 h⁻¹. At this dilution rate, only 71.0 ± 0.41% COD was removed whereas at a dilution rate of 0.1 h⁻¹, 98.2 ± 0.35% reduction in COD was achieved. At a dilution rate of 0.4 h⁻¹, the optimal yeast productivity and reduction in COD were 2.7 ± 0.13 g_p/1 h, and 84.2 ± 0.42%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhanced iturin A production by <Emphasis Type="Italic">Bacillus subtilis</Emphasis> and its effect on suppression of the plant pathogen <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

The behavior of Streptomyces peucetius var. caesius N47 was studied in a glucose limited chemostat with a complex cultivation medium. The steady-state study yielded the characteristic constants μ _max over 0.10 h⁻¹, Y _XS 0.536 g g⁻¹, and m_S 0.54 mg g⁻¹ h⁻¹. The product of secondary metabolism, ɛ-rhodomycinone, was produced with characteristics Y _PX 12.99 mg g⁻¹ and m _P 1.20 mg g⁻¹ h⁻¹. Significant correlations were found for phosphate and glucose consumption with biomass and ɛ-rhodomycinone production. Metabolic flux analysis was conducted to estimate intracellular fluxes at different dilution rates. TCA, PPP, and shikimate pathway fluxes exhibited bigger values with production than with growth. Environmental perturbation experiments with temperature, airflow, and pH changes on a steady-state chemostat implied that an elevation of pH could be the most effective way to shift the cells from growing to producing, as the pH change induced the biggest transient increase to the calculated ɛ-rhodomycinone flux.     

Production of lipase by high cell density fed-batch culture of Candida cylindracea

Candida cylindracea NRRL Y-17506 was grown to produce extracellular lipase from oleic acid as a carbon source. Through flask cultures, it was found that the optimum initial oleic acid concentration for cell growth was 20 g l⁻¹. However, high initial concentrations of oleic acid up to 50 g l⁻¹ were not inhibitory. The highest extracellular lipase activity obtained in flask culture was 3.0 U ml⁻¹ after 48 h with 5 g l⁻¹ of initial oleic acid concentration. Fed-batch cultures (intermittent and stepwise feeding) were carried out to improve cell concentration and lipase activity. For the intermittent feeding fed-batch culture, the final cell concentration was 52 g l⁻¹ and the extracellular lipase activity was 6.3 U ml⁻¹ at 138.5 h. Stepwise feeding fed-batch cultures were carried out to simulate an exponential feeding and to investigate the effects of specific growth rate (0.02, 0.04 and 0.08 h⁻¹) on cell growth and lipase production. The highest final cell concentration obtained was 90 g l⁻¹ when the set point of specific growth rate (μ_set) was 0.02 h⁻¹. High specific growth rate (0.04 and 0.08 h⁻¹) decreased extracellular lipase production in the later part of fed-batch cultures due to build-up of the oleic acid oversupplied. The highest extracellular lipase activity was 23.7 U ml⁻¹ when μ_set was 0.02 h⁻¹, while the highest lipase productivity was 0.31 U ml⁻¹ h⁻¹ at μ_set of 0.08 h⁻¹.     

Isolation of <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> mutants for heterologous protein production from a double proteinase gene disruptant

The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l⁻¹ h⁻¹, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition strategy, which reached 8.46 ± 0.31 g l⁻¹, 41.7 ± 1.4%, and 0.18 ± 0.01 g l⁻¹ h⁻¹ with the best continuous feeding strategy (0.2 g l⁻¹ h⁻¹), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L⁻¹ h⁻¹) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when the l-Met feeding rate reached 0.5 g l⁻¹ h⁻¹.     

Enhancement of polysaccharides production in <Emphasis Type="Italic">Ganoderma lucidum</Emphasis> by the addition of ethyl acetate extracts from <Emphasis Type="Italic">Eupolyphaga sinensis</Emphasis> and <Emphasis Type="Italic">Catharsius molossus</Emphasis>

To screen stimulators from Chinese medicinal insects for mycelial growth and polysaccharides production of Ganoderma lucidum, G. lucidum was inoculated into the media with and without supplementation of medicinal insect extracts. The ethyl acetate extract of Eupolyphaga sinensis at 55 mg l⁻¹ lead to significant increase in both biomass and intracellular polysaccharides (IPS) concentration from 8.53 ± 0.41 to 14.16 ± 0.43 and 1.28 ± 0.09 to 2.13 ± 0.11 g l⁻¹, respectively. In addition, the ethyl acetate extract of Catharsius molossus at 55 mg l⁻¹ significantly enhanced extracellular polysaccharides (EPS) production; the EPS yield increased from 350.9 ± 14.1 to 475.1 ± 15.3 mg l⁻¹. There were no new components in the two types of polysaccharides obtained by the addition of the insect extracts.     

High production of laccase by a new basidiomycete, <Emphasis Type="Italic">Trametes</Emphasis> sp

A new basidiomycete, Trametes sp. 420, produced laccase at 6,810 U l⁻¹ (268 mg, 25.4 U mg⁻¹ protein for guaiacol) in glucose medium and 7,870 U l⁻¹ (310 mg) in cellobiose medium with induction by 0.5 mM Cu²⁺ and 6 mM o-toluidine. Laccase isozyme E (LacE) was the sole laccase in the fermentation products. It was stable at pH 5–9 and below 70°C over 30 min. The K _m values of LacE for four substrates (guaiacol ABTS, 2,6-dimethoxyphenol and syringaldazine) varied from 5 to 245 μM. The activity of LacE was strongly inhibited by NaN₃ but not by EDTA or dimethylsulfoxide. LacE at 0.5 U l⁻¹ could decolorize industrial dyes. The open reading frame of the lacE gene was 2,130 bp and was interrupted by 10 introns. It displayed a high homology to laccases from other fungi. Pingui Tong and Yuzhi Hong contributed equally to the study     

Production of ascorbic acid glucoside by alginate-entrapped mycelia of <Emphasis Type="Italic">Aspergillus niger</Emphasis>

The mycelia of Aspergillus niger, cultivated in a medium containing 45 g l⁻¹ maltose, 66 g l⁻¹ yeast extract, and 5 g l⁻¹ K₂HPO₄ at 30°C and 200 rpm, were used as a biocatalyst in the glucosylation of ascorbic acid. Free mycelia from 3-day-old culture, when used in a 6-h reaction with maltose as the acyl donor, gave 16.07 g l⁻¹ ascorbic acid glucoside corresponding to a volumetric productivity of 2.68 g l⁻¹ h⁻¹ and a conversion of 67%. Mycelia from 3-day-old cultures were entrapped in calcium alginate beads and used as a catalyst in the glucosylation of ascorbic acid. An ascorbic acid-to-maltose molar ratio of 1:9 was found to be optimum, and the conversion reached 75% after 12 h. The concentration of ascorbic acid glucoside produced at this molar ratio was 17.95 g l⁻¹, and the productivity was 1.5 g l⁻¹ h⁻¹. The biocatalyst was repeatedly used in a fixed bed bioreactor for the synthesis of ascorbic acid glucoside and approximately 17 g l⁻¹ of ascorbic acid glucoside corresponding to a volumetric productivity of 1.42 g l⁻¹ h⁻¹ was produced in each use. The conversion was retained at 70% in each use. The entrapped mycelia also exhibited exceptionally high reusability and storage stability. The product was purified to 85% by anion exchange and gel permeation chromatography with a final yield of 75%.     

Kinetic studies of constitutive human granulocyte-macrophage colony stimulating factor (hGM-CSF) expression in continuous culture of <Emphasis Type="Italic">Pichia pastoris</Emphasis>

Extracellular human granulocyte-macrophage colony stimulating factor (hGM-CSF) expression was studied under the control of the GAP promoter in recombinant Pichia pastoris in a series of continuous culture runs (dilution rates from 0.025 to 0.2 h⁻¹). The inlet feed concentration was also varied and the steady state biomass concentration increased proportionally demonstrating efficient substrate utilization and constancy of the biomass yield coefficient (Y_x/s) for a given dilution rate. The specific product formation rate (q_P) showed a strong correlation with dilution rates demonstrating growth associated product formation of hGM-CSF. The volumetric product concentration achieved at the highest feed concentration (4×) and a dilution rate of 0.2 h⁻¹ was 82 mg l⁻¹ which was 5-fold higher compared to the continuous culture run with 1× feed concentration at the lowest dilution rate thus translating to a 40 fold increase in the volumetric productivity. The specific product yield (Y_P/X) increased slightly from 2 to 2.5 mg g⁻¹, with increasing dilution rates, while it remained fairly invariant, for all feed concentrations demonstrating negligible product degradation or feed back inhibition. The robust nature of this expression system would make it easily amenable to scale up for industrial production.     

Quasi steady state growth of <Emphasis Type="Italic">Lactococcus lactis</Emphasis> in glucose-limited acceleration stat (A-stat) cultures

Quasi steady state growth of Lactococcus lactis IL 1403 was studied in glucose-limited A-stat cultivation experiments with acceleration rates (a) from 0.003 to 0.06 h⁻² after initial stabilization of the cultures in chemostat at D = 0.2–0.3 h⁻¹. It was shown that the high limit of quasi steady state growth rate depended on the acceleration rate used—at an acceleration rate 0.003 h⁻² the quasi steady state growth was observed until μ _crit = 0.59 h⁻¹, which is also the μ _max value for the culture. Lower values of μ _crit were observed at higher acceleration rates. The steady state growth of bacteria stabilized at dilution rate 0.2 h⁻¹ was immediately disrupted after initiating acceleration at the highest acceleration rate studied—0.06 h⁻². Observation was made that differences [Δ(μ − D)] of the specific growth rates from pre-programmed dilution rates were the lowest using an acceleration rate of 0.003 h⁻² (< 4% of preset changing growth rate). The adaptability of cells to follow preprogrammed growth rate was found to decrease with increasing dilution rate—it was shown that lower acceleration rates should be applied at higher growth rates to maintain the culture in the quasi steady state. The critical specific growth rate and the biomass yields based on glucose consumption were higher if the medium contained S ₀ = 5 g L⁻¹ glucose instead of S ₀ = 10 g L⁻¹. It was assumed that this was due to the inhibitory effect of lactate accumulating at higher concentrations in the latter cultures. Parallel A-stat experiments at the same acceleration and dilution rates showed good reproducibility—Δ(μ − D) was less than 5%, standard deviations of biomass yields per ATP produced (Y _ATP), and biomass yields per glucose consumed (Y _XS) were less than 15%.     

Biotechnological production of <Emphasis Type="SmallCaps">l</Emphasis>-ribose from <Emphasis Type="SmallCaps">l</Emphasis>-arabinose

l-Ribose is a rare and expensive sugar that can be used as a precursor for the production of l-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing l-ribose from the readily available raw material l-arabinose. This was achieved by introducing l-ribose isomerase activity into l-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for l-ribose production by resting cells was investigated. The initial l-ribose production rates at 39°C and pH 8 were 0.46 ± 0.01 g g⁻¹ h⁻¹ (1.84 ± 0.03 g l⁻¹ h⁻¹) and 0.27 ± 0.01 g g⁻¹ h⁻¹ (1.91 ± 0.1 g l⁻¹ h⁻¹) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates having both l-arabinose isomerase and l-ribose isomerase activity were successfully used for converting l-arabinose to l-ribose.     

Transport of hemicellulose monomers in the xylose-fermenting yeastCandida shehatae

Summary Cells ofCandida shehatae repressed by growth in glucose- or D-xylose-medium produced a facilitated diffusion system that transported glucose (K _s±2 mM,V _max±2.3 mmoles g⁻¹ h⁻¹),d-xylose (K _s±125 mM,V _max±22.5 mmoles g⁻¹ h⁻¹) and D-mannose, but neither D-galactose norl-arabinose. Cells derepressed by starvation formed several sugar-proton symports. One proton symport accumulated 3-0-methylglucose about 400-fold and transported glucose (K _s±0.12 mM,V _max ± 3.2 mmoles g⁻¹ h⁻¹) andd-mannose, a second proton symport transportedd-xylose (K _s± 1.0 mM,V _max 1.4 mmoles g⁻¹ h⁻¹) andd-galactose, whilel-arabinose apparently used a third proton symport. The stoicheiometry was one proton for each molecule of glucose or D-xylose transported. Substrates of one sugar proton symport inhibited non-competitively the transport of substrates of the other symports. Starvation, while inducing the sugar-proton symports, silenced the facilitated diffusion system with respect to glucose transport but not with respect to the transport of D-xylose, facilitated diffusion functioning simultaneously with thed-xylose-proton symport.     

Carbon-limited fed-batch production of medium-chain-length polyhydroxyalkanoates from nonanoic acid by <Emphasis Type="Italic">Pseudomonas putida</Emphasis> KT2440

Pseudomonas putida KT2440 grew on glucose at a specific rate of 0.48 h⁻¹ but accumulated almost no poly-3-hydroxyalkanoates (PHA). Subsequent nitrogen limitation on nonanoic acid resulted in the accumulation of only 27% medium-chain-length PHA (MCL-PHA). In contrast, exponential nonanoic acid-limited growth (μ = 0.15 h⁻¹) produced 70 g l⁻¹ biomass containing 75% PHA. At a higher exponential feed rate (μ = 0.25 h⁻¹), the overall productivity was increased but less biomass (56 g l⁻¹) was produced due to higher oxygen demand, and the biomass contained less PHA (67%). It was concluded that carbon-limited exponential feeding of nonanoic acid or related substrates to cultures of P. putida KT2440 is a simple and highly effective method of producing MCL-PHA. Nitrogen limitation is unnecessary.     

Improving intracellular production of recombinant protein in <Emphasis Type="Italic">Pichia pastoris</Emphasis> using an optimized preinduction glycerol-feeding scheme

High-cell-density production of recombinant growth hormone of Lateolabrax japonicus (rljGH) expressed intracellularly in Pichia pastoris was investigated. In the regular strategy of induction at a cell density of 160 g l⁻¹, short duration of intracellular rljGH accumulation (17 h) resulted in a low final cell density of 226 g l⁻¹. Thus, a novel strategy of induction at a cell density of 320 g l⁻¹ was investigated. In this strategy, the preinduction glycerol-feeding scheme had a significant effect on the post-induction production. Constant glycerol feeding led to a decrease of the specific rljGH production and specific production rate because of low preinduction specific growth rate. This decrease was avoided by exponential glycerol feeding to maintain a preinduction specific growth rate of 0.16 h⁻¹. The results from exponential glycerol feeding indicated that the rljGH production depended on the preinduction specific growth rate. Moreover, mixed feeding of methanol and glycerol during induction improved the specific production rate to 0.07 mg g⁻¹ h⁻¹ from 0.043 mg g⁻¹ h⁻¹. Consequently, both high cell density (428 g l⁻¹) and high rljGH production could be achieved by the novel strategy: growing the cells at the specific growth rate of 0.16 h⁻¹ to the cell density of 320 g l⁻¹ and inducing the expression by mixed feeding.     

Improved hydrogen photoproduction regulated by carbonylcyanide <Emphasis Type="Italic">m</Emphasis>-chlorophenylhrazone from marine green alga <Emphasis Type="Italic">Platymonas subcordiformis</Emphasis> grown in CO<Subscript>2</Subscript>-supplemented air bubble column bioreactor

To develop an integrated process of CO₂-fixation and H₂ photoproduction by marine green microalga Platymonas subcordiformis, the impact of algal cells grown in CO₂-supplemented air bubble column bioreactor was investigated on H₂ photoproduction regulated by carbonylcyanide m-chlorophenylhrazone. Highest cell growth (3.85 × 10⁶ cells ml⁻¹), starch content (0.25 ± 0.08 mg per 10⁶ cells) and hydrogen production (50 ± 3 ml l⁻¹) were achieved at 3% CO₂-supplemented culture, which are respectively 1.4, 2.1, 1.5-fold of the air-supplemented culture. Improved H₂ production correlated well with the increase in starch accumulation. In this process, the algal cells have been recycled for stable H₂ production of 40–50 ml l⁻¹ over five cycles.     

A highly thermostable trehalase from the thermophilic bacterium <Emphasis Type="Italic">Rhodothermus marinus</Emphasis>

Trehalases play a central role in the metabolism of trehalose and can be found in a wide variety of organisms. A periplasmic trehalase (α,α-trehalose glucohydrolase, EC 3.2.1.28) from the thermophilic bacterium Rhodothermus marinus was purified and the respective encoding gene was identified, cloned and overexpressed in Escherichia coli. The recombinant trehalase is a monomeric protein with a molecular mass of 59 kDa. Maximum activity was observed at 88°C and pH 6.5. The recombinant trehalase exhibited a K _m of 0.16 mM and a V _max of 81 μmol of trehalose (min)⁻¹ (mg of protein)⁻¹ at the optimal temperature for growth of R. marinus (65°C) and pH 6.5. The enzyme was highly specific for trehalose and was inhibited by glucose with a K _i of 7 mM. This is the most thermostable trehalase ever characterized. Moreover, this is the first report on the identification and characterization of a trehalase from a thermophilic bacterium.     

Ethanol production from sweet sorghum juice in batch and fed-batch fermentations by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 10⁸ cells ml⁻¹ and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y _ps) and productivity (Q _p ) were 100 g l⁻¹, 0.42 g g⁻¹ and 1.67 g l⁻¹ h⁻¹ respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24 °Bx was one-time substrate feeding, where P, Y _ps and Q _p were 120 g l⁻¹, 0.48 g g⁻¹ and 1.11 g l⁻¹ h⁻¹ respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.