Journal of Fermentation Technology最新文献

A host-vector system for Zygosaccharomyces rouxii was developed. Chimeric plasmids useful as the Escherichia coli-Z. rouxii shuttle vector were constructed with a DNA fragment of pBR322, a fragment of pSR1 plasmid of Z. rouxii or the ARS1 sequence of Saccharomyces cerevisiae, and a fragment of the LEU2 gene of S. cerevisiae or a DNA fragment bearing Tn601 which confers G-418 resistance as a selective marker of the plasmid. For the hosts, wild-type strains of Z. rouxii were modified to give improved transformation frequencies or to mark a leucine-auxotrophic mutation which is complementable by the LEU2 DNA of S. cerevisiae. Transformation frequencies from several hundred to two thousand transformant clones per μg plasmid DNA samples were obtained.

The influence of water activity on 2-heptanone production (cheese aroma) by Trichoderma viride TS cultivated on agar media was evaluated through a headspace gas chromatographic analysis. Modifications in water activity (a_w) led to a number of variations in the aroma production (300% at 7 d). These variations could be attributed both to an increase in the production rate by the cells and to an increase in mycelial density. Optimal aroma production occurred at a_w=0.98, but considering the radial growth, the optimal a_w values were found to be both 0.96 and 0.98.

We carried out experiments designed to increase the production of cis-benzeneglycol from benzene by a mutant strain of Pseudomonas. Factors affecting the production were the temperature, the nitrogen source and it's concentration, the concentration of iron ions, and the benzene concentration. At a benzene concentration of 33% of saturation vapor pressure, the cis-benzeneglycol production was not stable, but this benzene concentration was not toxic to the cells. In a culture under 10% of saturation vapor pressure the cells kept producing cis-benzeneglycol for over 100 h.

The decrease in cis-benzeneglycol production observed production at high benzen partial pressure (33%) could not be accounted for by the combined effects of an inhibition of enzyme production and a rapid turn-over of the enzyme, but by a specific inactivation of the enzyme. Possible mechanisms of inactivation were discussed which could explain the specific inactivation of the benzene dioxygenase: generation of polyphenols or generation of oxygen radicals.

The development of a very sensitive and highly specific screening method for detection of new cell wall inhibitors of the fosfomycin type is described. A fosfomycin-hypersensitive mutant, f-360, was isolated from Staphylococcus aureus Newman by selection with fosfomycin, an antibiotic that inhibits synthesis of the bacterial cell wall. The mutant f-360 was 50-fold more sensitive than the parent strain to fosfomycin. The mutant was constitutive for the hexose phosphate transport system. Using the organism in screening, BA-3796, which had an antibacterial activity against mutant f-360 was found to be produced by a bacterium designated Bacillus sp. BA-3796. Starch and beef extract were the most suitable carbon and nitrogen sources for BA-3796 production and the amount of BA-3796 reached 3 g/l at a maximum level. The purified BA-3796 was identified as α-d-glucose-l-phosphate by its various physiochemical properties. α-d-Glucose-1-phosphate showes an antibacterial activity against Staphylococci in the presence of a slight amount pf α-d-glucose-6-phosphate.

The microbiological transformation of a sesquiterpene lactone, (−)-α-santonin was carried out by using Aspergillus niger MIL 5024 and MIL 5025. Strain MIL 5024 brings about the transformation of (−)-α-santonin (400 mg) to 11-hydroxy-(−)-α-santonin (P1) (50.4 mg), 3,6,9-trihydroxy-9,10-seco-selina-1,3,5(10)-trien-12-oic acid-12,6-lactone (P2) (22.4 mg), and 3,6-dihydroxy-9,10-seco-selina-1,3,5(10)-trien-9,12-dioic acid-12,6-lactone (P3) (27.1 mg), which were isolated and characterized by UV, IR, mass and ¹H-NMR spectroanalyses. All of these products are described for the first time. Results similar to those with MIL 5024 were also obtained from the transformation of (−)-α-santonin by the other isolate, strain MIL 5025.

Glucose-dehydrogenase-poly(ethylene glycol)-NAD conjugate (GlcDH-PEG-NAD) was prepared and its kinetic properties as an NADH-regeneration unit were investigated. The conjugate has about two molecules of active and covalently linked NAD per tetramer. The specific activity of the enzyme moiety of the conjugate in the presence of exogenous NAD is about 77% of that of the native enzyme, and this decrease is mainly due to the decrease in the V_max value. The conjugate has the same pH-stability profile as the native enzyme and an internal activity of 0.26s⁻¹ (as a monomer); its NAD moiety has similar coenzyme activity to poly(ethylene glycol)-bound NAD. These results indicate that GlcDH-PEG-NAD can be used as an NADH-regeneration unit for many dehydrogenase reactions. The coupled reaction of GlcDH-PEG-NAD and lactate dehydrogenase was then studied. The specific activity of the conjugate is 1.1 s⁻¹ (as a tetramer), the recycling rate of the active NAD moiety is 0.54 s⁻¹, and the apparent K_m value for glucose is 24 mM. Kinetically, lactate dehydrogenase behaves like a substrate with an apparent K_m value of 1.8 units·ml⁻¹ in this coupled reaction system with low coenzyme concentration. l-Lactate was continuously produced from pyruvate in a reactor with a PM10 ultrafiltration membrane, and containing GlcDH-PEG-NAD and lactate dehydrogenase. GlcDH-PEG-NAD proved to be applicable in continuous enzyme reactors as an NADH-regeneration unit with a large molecular size.