Synthesis of different pectinases by filamentous growing A. niger mutants.

Mutants of A. niger K 69/26, prepared by multistep mutagenesis (UV, MNNG, heating) have been screened for pectinase activities. Mutants with altered levels of certain pectinases, such as endo- and exopolygalacturonase (PG vis, red), pectinesterase (PE) and pectinlyase (PL), were isolated. The enzyme activities of the best mutants M 1348/126 were increased 2-3-fold compared to the parent strain after a 6-d cultivation of filamentous mycelium on a shaker. Further mutagenesis of mutants with decreased pectinase activities (e.g. Se3) produced revertants. PG (vis) synthesis of revertant Se5 was increased 1.7 times compared to the control strain K 69/26. Independent of these increased rates, the general level of pectinase activities synthesized by the filamentous mycelium of A. niger mutants amounts to about 10-20% compared with those produced by aggregated mycelium. It appears that the enzyme synthesis related to mycelium structure is independent of the mechanism which regulates the level of pectinase synthesis within a specific morphological structure.

Influence of culture conditions on mycelial structure and polygalacturonase synthesis of Aspergillus niger.

Biosynthesis of polygalacturonase (PG) by A. niger strain R 1/214 correlates with the morphology of mycelium in submerged culture. The mean specific PG-synthesis (PG-U.g-1.h-1) increases with the degree of compactness of mycelium. PG-production can be optimized by a precise adjustment of the culture conditions after direct spore inoculation (diffuse mycelium) but the high synthesis as by compact mycelium is never obtained. Different reasons for the higher enzyme production by the pellet mycelium are discussed. PG-synthesis is assumed to be strictly connected with a limitation of nutrient and oxygen supply.

[Germ reduction in technical enzyme preparations with special regard to gamma irradiation]. / Zur Keimminderung von technischen Enzympräparaten unter besonderer Berücksichtigung der Behandlung mit Gammastrahlen

For toxicological and hygienic reasons, the use of enzymes as technical additives is not admitted in various food industries if the germ counts of the preparations to be used exceed the respective tolerance values. In this connection, the authors report some results from attempts to reduce the germ content of a protease preparation, especially by gamma radiation. A gamma ray dose of I Mrad permitted to obtain germ-free preparations without considerable loss of enzyme activity.