Title The Proportion of Non-Aflatoxigenic Strains of the Aspergillus flavus/oryzae Complex from Meju by Analyses of the Aflatoxin Biosynthetic Genes
Author Seung-Beom Hong1*, Mina Lee1, Dae-Ho Kim1, Soo-Hyun Chung2, Hyeon-Dong Shin3, and Robert A. Samson4
Address 1Korean Agricultural Culture Collection, Agricultural Microbiology Division, National Academy of Agricultural Science, RDA, Suwon 441-707, Republic of Korea, 2Division of Food and Nutrition, College of Health Sciences, Korea University, Seoul 136-703, Republic of Korea, 3Division of Environmental Science and Ecological Engineering, College of Life and Environmental Science, Korea University, Seoul 136-701, Republic of Korea, 4CBS-KNAW Fungal Biodiversity Centre, 3508AD Utrecht, The Netherlands
Bibliography Journal of Microbiology, 51(6),766–772, 2013,
DOI 10.1007/s12275-013-3128-3
Key Words aflatoxin, Aspergillus flavus, Aspergillus flavus/oryzae complex, Aspergillus oryzae, Meju
Abstract Strains of the Aspergillus flavus/oryzae complex are frequently isolated from meju, a fermented soybean product, that is used as the starting material for ganjang (soy sauce) and doenjang (soybean paste) production. In this study, we examined the aflatoxin producing capacity of A. flavus/oryzae strains isolated from meju. 192 strains of A. flavus/oryzae were isolated from more than 100 meju samples collected from diverse regions of Korea from 2008 to 2011, and the norB-cypA, omtA, and aflR genes in the aflatoxin biosynthesis gene cluster were analyzed. We found that 178 strains (92.7%) belonged to non-aflatoxigenic group (Type I of norB-cypA, IB-L-B-, IC-AO, or IA-L-B- of omtA, and AO type of aflR), and 14 strains (7.3%) belonged to aflatoxin-producible group (Type II of norB-cypA, IC-L-B+/B- or IC-L-B+ of omtA, and AF type of aflR). Only 7 strains (3.6%) in the aflatoxin-producible group produced aflatoxins on Czapek yeast-extract medium. The aflatoxin-producing capability of A. flavus/ oryzae strains from other sources in Korea were also investigated, and 92.9% (52/56) strains from air, 93.9% (31/33) strains from rice straw, 91.7% (11/12) strains from soybean, 81.3% (13/16) strains from corn, 82% (41/50) strains from peanut, and 73.2% (41/56) strains from arable soil were included in the non-aflatoxigenic group. The proportion of non-aflatoxigenicity of meju strains was similar to that of strains from soybean, air and rice straw, all of which have an effect on the fermentation of meju. The data suggest that meju does not have a preference for non-aflatoxigenic or aflatoxin-producible strains of A. flavus/oryzae from the environment of meju. The non-aflatoxigenic meju strains are proposed to be named A. oryzae, while the meju strains that can produce aflatoxins should be referred to A. flavus in this study.