Comparison of acid-stable α-amylase production by Aspergillus kawachii in solid-state and submerged cultures

Abstract

The reasons why Aspergillus kawachii IFO4308 ( shochu white- koji mold) produced larger amounts of acid-stable α-amylase (asAA) in solid-state culture (SSC) than in submerged culture (SC) were studied. In both cultures, asAA began to be produced in the middle of the cultivation ( t 0) and in both cases, the production was approximately represented by a growth associated-type equation, asAA = k( m− m 0), where m and m 0 are the amounts of mycelia at t (≧t 0) and t 0 , respectively. The proportional constant between the amount of asAA produced and mycelial growth, k (mg-asAA/mg-dry mycelia) was 0.038 on average in SSC; this value was almost the same as the maximum k (0.034) obtained in a submerged medium suitable for asAA production (AP medium). In SSC, t 0 was shorter and the mold could grow more rapidly (logarithmically) after t 0 than in SC, resulting in larger amounts of ( m− m 0). Furthermore, in SSC k rose more readily to a ultimate value after t 0. These SSC characteristics were concluded to be the major reasons for the higher asAA production than in SC. On the other hand, it was considered that in SSC, similar to SC, asAA was produced when the content of storage glycogen (CSG) decreased, the triggers of asAA production being the low glucose concentration in the medium in the case of SC and the rapid mycelial re-growth in the case of SSC. asAA production is believed to be controlled not only by catabolite repression but also by an asAA production control mechanism.