Journal of Fermentation and Bioengineering最新文献

Dark fermentation in the marine green alga, Chlorococcum littorale, was investigated with emphasis on ethanol production. Under dark anaerobic conditions, 27% of cellular starch was consumed within 24 h at 25°C, the cellular starch decomposition being accelerated at higher temperatures. Ethanol, acetate, hydrogen and carbon dioxide were obtained as fermentation products. The maximum productivity of ethanol was 450 μmol/g-dry wt. at 30°C. The fermentation pathway for cellular starch was proposed from the yields of the end-products and the determined enzyme activities. Ethanol was formed from pyruvate by pyruvate decarboxylase and alcohol dehydrogenase. the change in fermentation pattern that varied with cell concentration in the reaction vials suggested that the hydrogen partial pressure affected the consumption mode of reducing equivalents under dark fermentation. Ethanol productivity was improved by adding methyl viologen, while hydrogen production decreased.

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.

The response surface method (RSM) was used to optimize the medium for the production of inulinase by Kluyveromyces sp. Y-85. The inulinase production was adequately approximated with a full quadratic equation obtained from a four-factor-five-level central composite design. Analyses of the quadratic surfaces showed that in a 24-h fermentation at 30°C, the maximum inulinase activity 59.5 U/ml appeared at extract of Jerusalem artichoke, urea, beef extract, corn steep liquor concentrations 8.0%, 2.0%, 0.2% and 4.0%, respectively. We further investigated the fermentation in 15 l fermentor and scaling-up in 1000 l tower fermentor. The inulinase activity in the scaling-up was 68.9 U/ml, which was the highest production reported at present, indicating that Kluyveromyces sp. Y-85 was an excellent strain for industrial production.

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.

Extractive lactic acid fermentation has recently been paid a great deal of attention. The problem with such a process is, however, that only undissociated lactate can be extracted. Therefore, lactic acid fermentation at low pH values is desirable. In the present study, we modified the metabolism of yeast (not lactic acid producing bacteria often cultivated at pH of 6–7) by expressing the lactate dehydrogenase (LDH) gene for the production of lactate at low pH values. For this purpose, the plasmid pADNS which contains the ADH1 promoter was used as a host vector, and a heterologous gene region, cDNA-LDH-A (encoding bovine lactate dehydrogenase) digested from plasmid pLDH12 was digested and ligated into the aforementioned two host vectors. The resultant plasmids were then transformed into Saccharomyces cerevisiae DS37. Using this recombinant S. cerevisiae strain, several batch and fed-batch fermentations at aerobic, microaerobic, and anaerobic conditions were conducted at several pH values (4.5-3.5). Since the recombinant S. cerevisiae produced a considerable amount of ethanol as well as lactate (about 10 g/l), we disrupted several pyruvate decarboxylase (PDC) genes to suppress the ethanol formation. Among the PDC genes, PDC1, PDC5 and PDC6, PDC1 had the greatest effect on the cell growth and ethanol production. The plasmid which containing the LDH-A structure gene was then transformed into the mutant strain lacking the PDC1 gene. Cultivation of this strain improved the lactate yield from glucose (from 0.155 to 0.20) while suppressing ethanol formation (from 0.35 to 0.20).

Aeromonas sobria LP004 harboring the Acinetobacter calcoaceticus lipase gene was designated as strain LP094. Lipase production of LP094 in WYGS medium [Lotrakul and Dharmsthiti, World J. Microbiol. Biotechnol., 13 : 163–166, 1997] was scaled up to a 50-l volume. LP094 lipase immobilized by ionic binding to either IR120 (Na⁺) or IRC50 (H⁺) Amberlite resins was found to retain more than 90% activity after 15 d storage at room temperature (≈ 25 to 30°C) or at 4°C. After 5 repeated lipid hydrolysis reactions, the activities of both immobilized preparations remained higher than 65%.

A 6955-bp sequence of a PstI-HindIII DNA fragment containing the manganese-superoxide dismutase (MnSOD) gene of Thermus aquaticus YT-1 was determined. The gene (sod) encoded a polypeptide consisting of 204 amino acid residues (the mature enzyme without the initiation methionine) with a calculated Mr of 22,773. The deduced amino acid sequence of the sod gene showed 92% identity to that of Thermus thermophilus HB8 determined chemically. The sod gene was well expressed in Escherichia coli and a heat-stable active enzyme was produced. An open reading frame encoding fumarase was found 91 bp upstream of the MnSOD gene in tandem form. The fum gene encoded a polypeptide consisting of 466 amino acid residues with a calculated M_r of 50,950. The deduced amino acid sequence of the fum gene product has similarity to that of the fumC of E. coli (57% identity), suggesting that this gene encodes a class II type fumarase.