The secret to the silkworm's healthy stomach

Silkworms have a unique ability to eat poisonous mulberry leaves without any harm, and scientists are gradually understanding why: silkworms contain a special digestive enzyme that is not infected. The toxic chemical of mulberry trees.

Mulberry leaves contain an extremely high amount of alkaloid chemicals that inhibit enzymes that break down sucrose (sugar), and are therefore a potential poison. However, there is a type of sucrose called beta-fructofuranosidase that is not infected with these toxic alkaloids.

Until now, this enzyme has not been found in any animal, but Toru Shimada and colleagues believe that this could explain the silkworm's unique ability to eat.

The researchers looked at the silkworm genome and discovered two fructofuranosidase genes, although only one gene was actually expressed in silkworms. This gene (abbreviated BmSuc1), is thought to concentrate in the silkworm gut, although surprisingly it is still commonly found in the silk glands. When separating enzymes from silkworms, the researchers found that the enzyme could still digest sucrose efficiently.

Silkworms are eating mulberry leaves.(Photo: Toru Shimada)

Shimada and colleagues note that more research is needed to determine whether this particular enzyme is the sole reason for the silkworm leaf's toxic resistance. It is possible that fructofuranosidases will appear in other insects that cannot eat mulberry leaves, which indicates the active side factors.

1. Article reference: Gen Daimon et al. B-fructofuranosidase of silkworm, Bombyx mori: Understanding the enzyme adaptation of B. mori with alkaloids in mulberry trees. Journal of Biological Chemistry. 2008; 283: 15271-15279