Evidence of transovarial transmission of Bacillus subtilis in the silkworm, Bombyx mori L.

Abstract Aim To investigate the transovarial transmission of Bacillus subtilis in the silkworm, Bombyx mori . Materials and methods A bacterium was isolated from the eggs of the silkworm, B. mori . A gene encoding 16S rRNA was amplified using PCR, sequenced and the bacterium was identified. To investigate the pathogenicity and transmission in the progeny of silkworm, bacterial suspensions of 1.0 × 10 6  CFU and 4.0 × 10 6  CFU was inoculated to the silkworm larvae individually. Bacterial infection in the tissues and larval mortality was recorded. Transovarial transmission in the progeny eggs of silkworms was evaluated using sequence homology of inoculated bacterium, isolated from the haemolymph of infected parent and from progeny eggs. Results A bacterium isolated from the eggs of silkworms was identified as B. subtilis . The pathogenic effect was observed in the form of 64–77% mortality during larval and pupal stages. The prevalence of pathogenic bacterium in the progeny eggs, laid by infected females confirmed that the bacteria inoculated to the parent was transmitted into progeny eggs. The results indicated that isolated bacterium as B. subtilis is pathogenic to B. mori causing 64–77% mortality during larval and pupa stages. The adults those survived infections, laid infected eggs evidence the sequence homology of B. subtilis isolated from infected parents and their progeny eggs. Thus this is the first report on transovarial transmission of a Bacillus sp. in insects. Conclusion Prevalence of pathogenic bacterium, B. subtilis isolated from eggs indicated transovarial transmission in the silkworm, B. mori . The transovarial transmission of B. subtilis was confirmed in the silkworm, B. mori on the basis of bioassay and 16S rRNA homology analysis.