Takaaki Naritomi

Effect of lactate on bacterial cellulose production from fructose in continuous culture

Abstract Bacterial cellulose (BC) was produced from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was performed in continuous culture and the effect of lactate on the production was investigated. In continuous culture with feeding of CSL-Fru medium containing 30 g· l −1 fructose at a dilution rate of 0.07 h −1 , a higher production rate (0.62 g· l −1 ·h −1 ) was obtained than that (0.40 g· l −1 ·h −1 ) in a batch culture using CSL-Fru medium with 70 g· l −1 initial fructose. However, when the dilution rate or fructose concentration in the feed medium were increased, the total yield of BC declined because the residual fructose concentration in the drawn broth increased. Supplementing 12.5 g· l −1 lactate to the feed medium increased the cell concentration and fructose consumption at a steady state, resulting in a production rate of 0.90 g· l −1 ·h −1 and a BC yield of 36% at a dilution rate of 0.1 h −1 . The ATP content of viable cells was maintained at a higher level by feeding a lactate-supplemented medium rather than the unsupplemented CSL-Fru medium. In a batch culture using lactate as the main carbon source, 77% of the lactate consumed was oxidized to CO 2 and only 6.9% was converted to BC. These findings indicated that lactate functioned as an energy source, not as a substrate for BC biosynthesis. Increased intracellular ATP resulting from lactate oxidation may have improved the fructose consumption and BC production in the continuous culture.

Effects of oxygen and carbon dioxide pressures on bacterial cellulose production by Acetobacter in aerated and agitated culture

Abstract With the aim of improving bacterial cellulose (BC) production in an aerated and agitated culture, the effects of the oxygen and carbon dioxide pressures were investigated. The BC production rate was dependent on the oxygen transfer rate, which declined as the broth viscosity increased, accompanied by BC accumulation. Increasing the partial pressure of oxygen by sparging with oxygen-enriched air and/or raising the operating pressure improved the oxygen supply, while the agitation power required was lowered. Although the BC production rate was not affected by higher oxygen pressure, it was reduced as the operating pressure was raised. The reduction in the production rate was considered to be due to the high carbon dioxide pressure, because carbon dioxide-enriched air also reduced the BC production rate, while the reduction was canceled out by increasing the air flow rate.

Regular paperEffect of ethanol on bacterial cellulose production from fructose in continuous culture

Effect of ethanol on bacterial cellulose (BC) production from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was investigated in continuous culture. Supplementation of 10 g·l−1 ethanol to the feed medium containing 30 g·l−1 fructose as the main carbon source enhanced the ATP content of viable cells, cell concentration, and fructose consumption rate, establishing a 72-h steady state with 0.95 g·l−1·h−1 of BC production rate and 46% of BC yield in continuous culture with a dilution rate of 0.07 h−1. However, an increase in concentration of ethanol to more than 15 g·l−1 decreased BC production rate due to the inhibition of cell growth by the generated acetate. Results from batch culture experiment using ethanol as the main carbon source suggested that ethanol functioned as an energy source for ATP generation, and not as a substrate for BC biosynthesis. On the other hand, fructose hexokinase (FHK) activity was increased and activities of glucose 6-phosphate dehydrogenases (G6PDs) were inhibited by ATP, suggesting that the improved BC production from fructose by ethanol supplementation was a result of increased fructose dissimilation and abundant flow of glucose 6-phosphate (G6P), a precursor of BC, into the BC biosynthetic pathway due to the inhibition of G6PDs by increased levels of ATP.

Continuous anaerobic treatment of wastewater from a kraft pulp mill

Abstract A pilot-scale study of the thermophilic anaerobic digestion of high-strength wastewater (evaporator condensate, EC) discharged from a kraft pulp production process was performed. The system consisted of a microfiltration (MF) membrane module for oily substances removal, a stripping system using evolved gas from the digester for sulfur compounds removal, an anaerobic fixed-bed bioreactor for methane fermentation, and an ultrafiltration (UF) membrane module for retention of a high density of bacterial cells. The bioreactor had a fixed-bed with an effective volume of 5 m 3 packed with pumice stone. In a continuous run with only the MF membrane module for oily substances removal, the digester efficiency declined because of methanogenic inhibition by sulfur compounds. After fitting of the stripping system which used evolved gas from the digester, the inhibitive sulfur compounds in the EC were removed more than 80%, and high-loading and high-efficiency operation could be attained. The BOD loading and BOD removal of 35.5 kg BOD/m 3 /d and 93%, respectively were attained. By anaerobic treatment of the evaporator condensate waste before the conventional aerobic activated sludge method, the total costs would be reduced to ¥3.31/m 3 wastewater compared with ¥4.53/m 3 -wastewater by the aerobic activated sludge method only. The stability of digester performance against interruption by feed stoppage was also examined.

Influence of broth exchange ratio on bacterial cellulose production by repeated-batch culture

Abstract The influence of broth exchange ratio on bacterial cellulose (BC) production by repeated-batch culture using Acetobactor xylinum subsp. sucrofermentans BPR3001A was investigated. When repeated-batch cultures were conducted at various broth exchange ratios ( α ), the highest BC production rate (0.43 g l −1 h −1 ) and BC yield (28%) were obtained at α of 0.9. With a larger α than 0.9, the ATP content was lower than that at α of 0.9 and the culture time was prolonged, resulting in a lower BC production rate. On the other hand, with a smaller α than 0.9 the dissolved oxygen could not be maintained at 10% of air saturation and CO 2 evolution from fructose increased, resulting in a lower BC yield, whereas the ATP content maintained higher level than that at α of 0.9. When six cycles of repeated-batch culture were conducted with α of 0.9, at least four cycles of repeated-batch culture were possible with a BC production rate of 0.42 g l −1 h −1 and a BC yield of 28% on average, and BC productivity was 2.5 times higher than that in single batch culture.

Enzyme activity for monitoring the stability in a thermophilic anaerobic digestion of wastewater containing methanol

To maintain good conditions in a thermophilic methane bioreactor treating methanol as the main substrate, microbial enzyme activity in the reactor was investigated. In a preliminary study, seven enzymes were tested for their suitability as indicators using an acid-former, 22a originating from a digester with low efficiency, Methanosarcina sp. (CHTI-55) and Desulfotomaculum nigrificans (Delft 74). Among the tested strains, the activities of seven enzymes were the highest in 22a. Acidic phosphatase (ACP), glutamic-pyruvic transaminase (GPT) and α-amylase (AMY) were chosen as hopeful indicators for lab-scale tests and their activities were measured at the optimum temperature of 55°C. In the lab-scale test, reactor failure was induced by nitrogen deficiency or addition of dimethyl disulfide (DMDS) as an inhibitor. ACP, GPT and AMY outperformed the conventional parameters as indicators of any instability in the process.

Effect of glutamate on extracellular corrinoid production by a thermophilic, methanol-utilizing methanogen, Methanosarcina sp. CHTI 55

Abstract Addition of glutamate increased the extracellular corrinoid production by a thermophilic, methanol-utilizing methanogen, Methanosarcina sp. CHTI 55 (DSM 2906) in batch and continuous cultures. Increases in glutamate oxaloacetate transaminase (GOT) activity and the concentration of 5-aminolevulinic acid (ALA) as a result of the glutamate addition suggested that the increase in extracellular corrinoid production was caused by the stimulation of ALA biosynthesis.