土壌サンプル中のアフラトキシン産生菌の生残を調査するための寒天培地全量抽出法

Abstract

In this study, we investigated a method of extracting the whole agar dish culture to assess the existence and survival of producing fungi of aflatoxins (AFs) in field soil samples. In a control experiment using a known aflatoxigenic Aspergillus flavus strain with dichlorvos (DV) - coated agar or DV-free agar, no significant difference on the recovery of colony numbers was observed while DV clearly inhibited AFs accumulation. Therefore, a method of extracting the whole dish culture of DV-free agar followed by aflatoxin B1 (AFB1) analysis was applied to assess the survival of aflatoxigenic fungi in soil samples during storage. Soil samples stored at different temperature (4°C, -20°C, and -80°C) and duration (3-12 months) were cultured and analyzed for the accumulation of AFB1 in triplicate. Each soil sample suspension was cultured on DV-free agar for 7 days at 25°C, and the whole dish culture was extracted by methanol and the amount of AFB1 was measured. AFB1 amounts were drastically decreased after the fourth month of storage at all temperatures tested. After the fifth month, AFB1 amounts of samples stored at 4°C were significantly lower than those stored at -20°C or -80°C, indicating that temperatures below -20°C may be suitable for longer storage of soil samples. This whole dish culture extraction method is easy to handle and will be applicable to estimate the population of aflatoxigenic fungi among various soil samples from different origin or conditions.