Journal of Fermentation and Bioengineering最新文献

The plant hormone abscisic acid (ABA) induces a morphological change from green vegetative cells to red cyst cells, of Haematococcus pluvialis containing carotenoids, in plate culture. Long-lasting analogs of ABA, (+)-8′,8′,8′-trifluoro and (+)-8′,8′-difluoro-ABAs, which can resist metabolic inactivation, induce carotenoid production at 100-fold lower concentration than (+)-ABA. These analogs can be used as effective regulators to produce carotenoids in H. pluvialis cells.

Clostridia are well-known obligatory anaerobic bacteria which cannot utilize oxygen, or otherwise die in oxygenated environments. Clostridium butyricum, the type species of the genus Clostridium, possesses the ability to consume oxygen in amounts proportional to the size of the inoculum. Oxygen consumption was observed when NADH and NADPH were added to the cell extract of this strain. NADH oxidase and NADPH oxidase activities were also detected in all of the tested strains of the genus Clostridium. C. butyricum ceased growing while consuming oxygen in the medium. After consumption of all the dissolved oxygen, C. butyricum resumed growth at a rate equivalent to its anaerobic growth rate, suggesting that no oxidative damage based on oxygen reduction occurs in vivo. As scavengers for active oxygen species, the activities of $\text{NADH}\text{NADPH}$ peroxidase and SOD were detected in C. butyricum. Furthermore, the activities of these enzymes are distributed widely in the genus Clostridium.

A ceramic filter was fitted in a stirred ceramic membrane reactor (SCMR) for both extraction of culture supernatant and feeding of distilled water in reverse flow. The dependence of filtration performance on the cell concentration was decreased by about 20% by regularly cleaning the filter using a membrane cleaning system. The improved permeability effected an increase of both the growth rate and viability of Lactococcus lactis by increasing the dilution rate of the culture supernatant. Using the improved SCMR system, a cell concentration of 178 g/l and viability of 98% were obtained after 198 h of culture, while it took 238 h to obtain a cell concentration of 141 g/l and 94% viability without the use of the membrane cleaning system. The perfusion culture system was applied to the rapid batch fermentation of lactic acid by retaining cells at a high density in the SCMR. When the cell concentration reached 80 g/l, the culture supernatant was extracted and replaced with the fermentation medium. Batch fermentation using the retained cells was repeated six times. The concentration of lactic acid increased to more than 30 g/l within 2 h in each fermentation, while 1.2 h was necessary for replacing the culture supernatant to repeat the batch fermentation. The production rate of lactic acid was increased in proportion to the cell concentration, and a high fermentation activity of the retained cells was maintained via the repeated batch fermentation. These results demonstrate that the improved permeability of the SCMR with use of a membrane cleaning system effected a rapid increase in the concentration and viability of cells, and accordingly, the increased production rate of lactic acid in proportion to the concentration of viable cells.

Alanine racemase gene fragments containing non-conserved regions of the gene were evaluated as probes for detecting Bacillus stearothermophilus and Bacillus psychrosaccharolyticus in foods. The gene fragments were amplified from genomic DNA of each bacterium by polymerase chain reaction with degenerate oligonucleotide primers, and labeled with digoxigenin as probes for detecting each bacterium. Foods and bacteria were treated at 25°C for 10 min in 0.1 N NaOH containing 0.5% SDS before being directly spotted onto nylon membranes for DNA hybridization. When the specificities of the probes were analyzed using a total of 86 strains (23 genera and 65 species) of bacteria including 29 Bacillus strains (20 species), each probe was specific for the respective target bacteria. A variety of foods inoculated with B. stearothermophilus or B. psychrosaccharolyticus were positive as determined by hybridization with the respective probe, whereas uninoculated foods were negative. The alanine racemase gene fragments could be used as specific probes for detecting B. stearothermophilus and B. psychrosaccharolyticus in foods.

A strain of Agrobacterium tumefaciens isolated from soil was cultivated under various conditions in shake flasks to study exopolysaccharides (EPS) production. NMR analysis revealed that the EPS obtained was a succinoglycan-like polymer. Optimal yields of EPS were obtained using sucrose and lysine as the carbon and nitrogen sources, respectively. Supplementation of the medium with various chemicals resulted in a more or less marked effect on the polymer yield and properties: in particular, high phosphate levels and non-ionic surfactants led to the production of polymers of different molecular sizes in yields up to 13.7 g/l. Oxygen availability also affected the polymer yield and quality. The chemical structure was substantially unaffected by the various fermentation conditions tested. A fermentation carried out in a laboratory-scale fermentor yielded 9.6 g/l succinoglycan from 15 g/l sucrose in the basic medium without further supplements.

A facile synthetic method for a cupreous chafer beetle sex pheromone (R,Z)-(−)-5-(1-octenyl)oxacyclopentan-2-one has been developed by employing lipase-catalyzed enantioselective acylation of racemic 4-hydroxy-5-dodecynonitrile in an organic solvent.

For the purpose of separating microorganisms from culture broth by magnetic force, magnetic particles were conjugated with a polymer to produce polymer-conjugated magnetite (polymer-mag). Among 4 preparation methods investigated—aminosilane coupling, glycidylsilane coupling, crosslinking, and co-precipitation—, polymer-mag prepared by co-precipitation showed the highest cell recovery and high dispersibility. When various cationic, anionic, and nonionic polymers were used to prepare polymer-mag and applied to the magnetic separation for Escherichia coli, magnetite conjugated with chitosan (chitosan-mag) gave the highest cell recovery. In addition, E. coli cells could be recovered as the precipitant only 1 min after chitosan-mag was added to a cell suspension, and a clarified supernatant was obtained. The amount of E. coli cells adsorbed to the chitosan-mag was about 1 g-dry cells/g-chitosan-mag, and cell recovery of over 90% was attained in wide pH range from 3.0 to 7.0. Of 12 microorganisms tested, 4 could be recovered with chitosan-mag at recovery levels above 90%, and the adsorbed amounts exceeded 0.5 g-dry cells/g-chitosan-mag. Differences in adsorbed amounts were considered to be mainly due to the different zeta potential of the microorganisms tested.

Sugar feeding based on the CO₂ production rate was investigated for the control of the cell growth rate during cephalosporin C fermentation in which sugar concentration was the growth limiting factor. The rates of cell growth and sugar consumption were apparently influenced by the sugar feed rate, as the sugar concentration in the broth was kept at approximately 1 g/l during the cultivation. The ratio of the CO₂ production rate to the sugar consumption rate was maintained almost constant after 40 h cultivation. Stepwise alteration in sugar feed rate after the culture time of 50 h caused a change in the CO₂ production rate within 15 min. These results indicated that the CO₂ production rate could be used as an effective parameter of sugar consumption and cell growth rates. Consequently, a control strategy was developed that involved the control of sugar feed rate so that a CO₂ production rate profile corresponded to a preset standard profile. For the half the usual amount of inoculum, the sugar feeding control system enabled the cell concentration to increase faster to that in the usual inoculum. The cell concentration deviation during exponential growth phase among several batches, decreased to half using this sugar feeding control system compared to the culture without such control. These results indicated that the sugar feeding control system developed in this report was found to be efficient for control of cell growth.