Aspergillus oryzae is GRAS (generally recognized as safe) and various type of strains are used in the industry. The A. oryzae genome sequence analysis conducted in 2005, revealed the presence of many conserved secondary metabolism clusters in A. oryzae. In these studies, a cluster similar to the gliotoxin synthesis cluster was identified in the A. oryzae genome. Recently, the product of this cluster was identified as aspirochlorine (ACL), and this cluster was designated as the ACL cluster. ACL is antibiotics A30641, which inhibits fungal protein synthesis and represses the growth of Candida albicans. Although, some A. oryzae strains are known to produce ACL, the ACL productivity in several A. oryzae strains remain unclear. In this study, we investigated the physiological and molecular biological features of ACL productivity among different A. oryzae strains. First, we investigated ACL productivity in 3 different media (WATM, CYA, YES) in agar plate condition and rice koji condition by using A. oryzae RIB40. We observed that the amount of ACL was different in each plate culture medium. However, in rice koji conditions, RIB40 did not produce ACL even after 8 days of cultivation. We then examined the ACL production of 13 A. oryzae strains, one from each of the 13 phylogenetic clusters of A. oryzae. We examined the ACL productivity of these strains in YES agar medium, as RIB40 showed the maximum ACL production; ACL productivities among these strains were considerably different. In particular, RIB301, RIB430 and RIB1172 did not produce ACL. Furthermore, we examined the ACL production by these strains in rice koji conditions and found that none of the strains produced ACL. This difference in ACL productivity likely be based on the difference between the ACL cluster genes sequences. Hence, we examined the genome sequence of ACL clusters in these 13 strains. The ACL cluster was found to be conserved in all the 13 strains and many mutations were found in each strain. Some strain-specific mutations were also observed; in particular, in the strains that did not produce ACL. In this study, it is clear that ACL productivity is affected by nutrient conditions. Interestingly, in the rice koji condition, no strains produced ACL, and it supposed that Japanese sake does not contain ACL. Hence, we investigated the ACL concentration in Japanese sake. We collected 11 types of sake from 20 prefectures, and did not find ACL.
Full conference title:
The Fourteenth International Aspergillus Meeting, Asilomar Conference Center, Pacific Grove, CA, USA
- Asperfest 14 (2017)