Two cells of the dinoflagellate Alexandrium catenella

A lethal nerve agent called saxitoxin is produced by marine plankton (above) and freshwater bacteria. Credit: Donald Anderson

Biochemistry

How bacteria build a deadly toxin

Insights into an enzyme could yield new anaesthetics.

Scientists have revealed the first steps involved in a microbe’s synthesis of a potent nerve toxin. The advance could help to make the compound, saxitoxin, medically useful.

Saxitoxin is made by aquatic bacteria and plankton. Although humans can die from eating shellfish contaminated with it, the compound’s nerve-blocking activity might make it useful as a long-lasting anaesthetic. Alison Narayan at the University of Michigan in Ann Arbor and her colleagues investigated an enzyme involved in manufacturing saxitoxin in the bacterium Cylindrospermopsis raciborskii T3.

First, the authors determined which chemical ingredients the enzyme uses as a feedstock. Then the team fed alternate forms of one ingredient to the enzyme, which made saxitoxin precursors that differed slightly from the one produced under natural conditions.

The modified precursors could lead to forms of saxitoxin mild enough to act as a drug rather than a poison.