Journal of Fermentation and Bioengineering最新文献

Fungal growth inhibition by ethanol was compared with that caused by five other agents of water stress (at 25, 40 and 42.5°C), using Aspergillus oryzae. Ethanol, KCl, glycerol, glucose, sorbitol, and polyethylene glycol 400 were incorporated into media at concentrations corresponding to water activity (a_w) values in the range 1 to 0.75. Generally, as temperature increased there was a decrease in the a_w value at which optimum growth occurred. The a_w limit for growth on KCl, glycerol, glucose, sorbitol, or polyethylene glycol 400 media was about 0.85, regardless of temperature. However, the a_w limit for growth on ethanol media varied between 0.97 and 0.99 a_w and was temperature-dependent. Water stress accounted for up to 31, 18 and 6% of growth inhibition by ethanol at 25, 40, and 42.5°C, respectively. For media containing ethanol, the decrease in growth rate per unit of a_w reduction was greater as temperature increased. However, ethanol-induced water stress remained constant regardless of temperature, suggesting that other inhibitory effects of ethanol are closely temperature-dependent. Water stress may account for considerably more than 30% of growth inhibition by ethanol in cells that remain metabolically active at higher ethanol concentrations.

The biomass concentration in a bubble column reactor was estimated by analyzing the conductivity change during high-density culture of Catharanthus roseus hairy roots. The accumulated biomass in the reactor was estimated from the amount of nutrients consumed, which were present in the liquid medium. Liquid medium, consisting of water and nutrients, was incorporated into the biomass, in proportion to the growth of hairy roots, consequently the ratio of the volume of liquid medium to the volume of the biomass decreased continuously. To evaluate nutrient consumption, the change in biomass volume in the reactor was introduced as a new parameter for biomass estimation. After 45 d of culture, the final concentration of hairy roots was 46.5 g dry wt./l, of which the biomass volume is about 40% of the total culture volume of the reactor. A conventional conductivity method, in which the volume change of the liquid medium was not considered, resulted in a deviation (55.76 g dry wt./l) of about 20% from the actual biomass. This procedure yielded a value of 47.1 g dry wt./l of hairy roots, which is a nearly accurate estimation of the biomass concentration. This result suggests that the volume reduction of liquid medium should be considered for biomass estimation and process control for high-density plant cell cultures.

The synthesis of the four possible stereoisomers of 21-methyl-8-pentatriacontene, the (R)- and (S)-enantiomers of both (Z)- and (E)-geometrical isomers, was achieved by starting from the enantiomers of 3-hydroxy-2-methylpropionate, 1-nonyne and 1,10-decandiol to evaluate the response of the male yellow-spotted longicorn beetle, Psacothea hilaris.

Peptide ligands which bound to a model monomeric protein, bovine pancreatic ribonuclease A, could be isolated from a constrained random hexapeptide phage library. Selection was successful in a low ionic strength buffer (10 mM sodium phosphate, pH 6.0), whereas it failed in TBS (50 mM Tris-Cl, 150 mM NaCl, pH 7.5). Two of the displayed amino acid sequences from among the clones isolated were AEGACEQLDYNC and AEGACLWHDQLC. Electrostatic interaction appeared to play an important role in the binding because these phages could not bind to RNase A at a high ionic strength. The results suggest that selection in low ionic strength buffers could make possible the isolation of peptide ligands against proteins of interest which do not originally interact with another peptide or protein.

Fed-batch cultures were performed to improve the productivity of erythritol. When only glucose was added to the culture broth, the specific erythritol production rate was markedly decreased from 0.042 g/g/h to 0.023 g/g/h. On addition of both glucose and corn steep liquor, the rate was kept almost constant at 0.042 g/g/h throughout the fed-batch fermentation period. The repeated fed-batch culture method showed a maximum erythritol productivity of 1.86 g/l/h and a 45% of total erythritol conversion yield, corresponding to a 23% and 15% increase compared with batch fermentation.

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.

The chiA gene encoding chitinase A was cloned into Escherichia coli from Xanthomonas sp. strain AK and its nucleotide sequence was determined. The structural gene consists of 1788 bp encoding 596 amino acids with a predicted molecular weight of 62,122. The deduced ChiA is a modular enzyme composed of an N-terminal signal peptide and four domains in the following order: a chitin-binding domain, two fibronectin type III domains, and a family 18 catalytic domain. ChiA purified from the recombinant E. coli had temperature and pH optima at 35°C and 4.5, respectively. The K_m and V_max values for colloidal chitin were estimated to be 1.8 mg/ml and 8.7 μmol/min/mg, respectively.

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.

The chitinolytic activity of Penicillium janthinellum P9 was studied in shaken cultures and in a 3-l bench-top bioreactor by varying culture conditions such as initial medium pH, growth temperature, stirrer speed and aeration site. In shaken flasks, the highest levels of enzyme activity (468 and 483 U·l⁻¹) were obtained at a growth temperature of 24°C and at an initial medium pH of 4.0, respectively. In the bioreactor, both agitation and aeration significantly influenced the enzyme production: the highest level of enzyme activity (497 U·l⁻¹) was obtained at an impeller speed of 500 rpm and an aeration rate of 1.5 vvm. Culturing P. janthinellum P9 under optimised conditions led to an increase in the enzyme activity of ca. 65% (686 U·l⁻¹ as compared to the 415 U·l⁻¹ obtained under the initial culture conditions).