By Arran Frood

Bacteria such as E.coli are being used to help manufacture the propellant

The microbes help make a key ingredient of a fuel mix used in missiles but could also reduce the cost of drugs used to lower cholesterol levels.

The US military commissioned the work after discovering navy chemists were using the cheaper, but more dangerous, chemical nitroglycerine in its place.

Details are published in the Journal of the American Chemical Society.

The conventional manufacture of the propellant butanetriol costs $30 (£16) to $40 (£22) per pound. Together, the Navy and Army purchase about 15,000 pounds (6,803 kg) per year.

Butanetriol is used to make another chemical called butanetriol trinitrate (BTTN) which is employed in the fuel mix of missiles such as the Hellfire, an air-to-ground attack missile fired from military helicopters such as the Apache and unmanned Predator drones.

Reducing costs

If the costs of producing butanetriol could be reduced to $10 (£5) or $15 (£8) per pound, demand from the two armed forces could rise to 180,000 pounds (82,000 kg) per year, replacing nitroglycerine in many military and civilian applications.

The process will make missiles cheaper to manufacture

Scientists are always on the look out for safer alternatives to nitroglycerine as it is notoriously volatile.

The brother of Swedish chemist Alfred Nobel died in an accident during an attempt to manufacture the chemical - a process that later made Alfred rich.

He used the proceeds to launch the coveted Nobel prizes for science, peace, economics and literature that are still awarded today.

There are safer alternatives to nitroglycerine, but the chemical is effective and cheap to produce.

As a result, some two million pounds (907,000 kg) of it are made each year, carrying the same hazards during manufacture that confronted Nobel in the 1860s.

Even burn

By modifying key genes in the bacteria E. coli and Pseudomonas fragi, researchers led by Dr John Frost of Michigan State University, US, have teased the microbes into making butanetriol from simple carbohydrates obtained from corn and sugar beet.

The key aspect is simplicity, we are teaching the microbes to be chemical catalysts Dr John Frost, Michigan State University

The butanetriol is then nitrated to produce BTTN, which allows the missile rocket's propellant mix to burn more evenly, similar to the way that some cigarette paper is treated.

"The key aspect is simplicity, we are teaching the microbes to be chemical catalysts," said Dr Frost. "At the moment we are using two bacteria, but the goal is to refine the process to just one step. Microbes allow you to deal in large volumes, which make the process commercially viable.

"Compared with nitroglycerine, which is pretty unforgiving stuff, the BTTN is safer in all aspects of manufacture and use."

Biological factories

He adds that the bio-production of butanetriol is easier and less polluting than its conventional synthesis because it takes place between room and body temperature and at normal atmospheric pressure.

Naturally occurring bacteria have been used to make bread, cheese, beer and wine.

More recently, bacteria have been turned into tiny biological factories by genetic modification to produce a variety of chemicals: antibiotics, nylon derivatives and human insulin for diabetes sufferers.

The production of butanetriol using bacteria is an unusual combination of technologies with green credentials, though the ultimate product is controversial.

But there are wider benefits for human health: butanetriol is also a chemical precursor to two cholesterol-lowering drugs prescribed to those at risk of a heart attack.