Aspergillus bombycis genotypes (RFLP) from silkworm cultivation

Eighteen isolates of Aspergillus bombycis from samples of dust, insect frass, and soil collected from eight silkworm rearing facilities in Japan, as well as single silkworm rearing facilities in Indonesia and Malaysia, were subjected to DNA fingerprinting. PstI digests of total genomic DNA from each isolate were probed using the pAF 28 repetitive sequence. Among 18 isolates analyzed, 7 distinct DNA fingerprint groups were identified, including GTAb-2 isolated from rearing facilities in four prefectures of Japan. Aspergillus bombycis isolates share several features in common with domesticated yellow-green aspergilli, the koji molds used in traditional Oriental food fermentations, including a loose and deep colony texture, smoothwalled stipes, and the absence of sclerotia. Although aflatoxin is unknown from koji molds, all isolates of A. bombycis produced B and G aflatoxins. Aflatoxin has been linked to increased virulence in Aspergillus disease of silkworms, and there should be strong selection for aflatoxin production among clonal populations of A. bombycis adapted to silkworm cultivation. A hypothesis is offered that A. bombycis isolates from silkworm cultivation represent highly adapted forms of yet to be discovered “wild” populations that may infect Bombyx mandarina.