Katsuo Wako

Breeding of a mutant of Aureobasidium sp. with high erythritol production

Abstract An erythritol-producing yeast, Aureobasidium sp. SN-124A, was successively mutated with UV irradiation and NTG treatment. One of the isolated mutants, SN-G42, had superior properties to the wild strain in the following three points. First, SN-G42 did not foam during cultivation while the wild strain foamed severely. This property of the mutant greatly facilitated its cultivation in the fermentor. Second, the mutant produced erythritol with 47.6% yield on a medium containing 22.5% glucose compared to 41.8% yield obtained with the wild strain. Third, the yield in the wild strain declined from 41.8% to 14.2% when the glucose concentration of the medium was increased from 22.5% to 47%. On the contrary, the yield in the mutant decreased only from 47.6% to 37.7% under the same conditions. As a result, the maximum erythritol concentration produced reached 164.8 mg/ml with the mutant while the highest value obtained with the wild strain was 110 mg/ml. These properties of the isolated mutant made it possible to produce erythritol on a commercial scale.

Purification and some properties of a novel maltohexaose-producing exo-amylase from Aerobacter aerogenes.

Maltohexaose producing amylase (EC 3.2.1.-) is the fourth known exo-amylase, the three previously known being glucoamylase, beta-amylase and Pseudomonas stutzeri maltotetraose producing amylase. The enzyme after release from Aerobacter aerogenes cells by 0.1% sodium lauryl sulfate extraction was purified by ammonium sulfate precipitation, DEAE-Sephadex column chromatography and Sephadex G-100 gel filtration to 80-fold of the original sodium lauryl sulfate extract activity, It gave a single band on disc electrophoresis, and the molecular weight by gel filtration was 54 000. This amylase showed maximal activity at 50 degrees C and pH 6.80. The pH stability range was relatively wide, the enzyme retaining more than 90% of its initial activity in the range of 6.50-9.0. 80% of the activity was retained after 15 min at 50 degrees C. This enzyme produced maltohexaose from starch, amylose and amylopectin by exo-attack, but did not act on alpha- or beta-cyclodextrin, pullulan or maltohexaitol. Also the enzyme acted on beta-limit dextrins of amylopectin and glycogen to form branched oligosaccharides. The unusual reaction of this enzyme on beta-limit dextrin is discussed from the standpoint of the stereochemistry of 1,4-alpha- and 1,6-alpha-glucosidic bonds. This is the anomalous amylase for which it is recognized that 1,6-alpha-glucosidic linkages in the substrates can mimic the effect of 1,4-alpha-bonds, as previously observed in pseudo-priming reactions of E. coli phosphorylase.