Science: Microbe of the Month: Worm's turn to do the biological laundry: An enzyme from a mollusc will create a cleaner wash, says Bernard Dixon
Monday 12 July 1993
A splendid example of the third case was laid before the Sixth European Congress on Biotechnology held in Florence last month. They heard of a bacterium, isolated from a mollusc related to clams, scallops and oysters, which produces an enzyme that may well find an important role in biological washing powders.
Like the enzymes already incorporated in some detergents, it attacks proteinaceous stains - such as blood, egg, grass and sweat - that adhere strongly to textile fibres. But it can also break down proteins over an unusually wide range of temperatures, and is specially suited for washing powders because it lacks the sodium tripolyphosphate now being eliminated on environmental grounds.
The concept of enzyme detergents goes back to the beginning of this century, when chemists first incorporated protein-digesting enzymes (proteases), extracted from pancreatic glands, in laundry pre-soaks. They hoped that trypsin and other proteases would break down protein stains, but these experiments were only partially successful.
The first commercially successful biological detergent became possible in the early Sixties when the Danish company Novo launched a product known as Alcalase. The protease in this was not only effective in digesting protein stains. It was also unaffected by the other components of washing powder, and worked at then routine high temperatures. The Dutch firm Kortman & Schulte, in collaboration with Gebruder Schnyder in Switzerland, used Alcalase in Biotex, a breakthrough in enzyme detergents. A temporary setback in the Seventies, when the enzyme powders caused allergic reactions in a few factory workers, was soon overcome by encapsulating the enzymes in a tough coating.
The discovery announced in Florence arose from studies at the Agricultural Research Service in Peoria, Illinois. Richard Greene and two colleagues at the US Department of Agriculture, Harold Griffin and Michael Cotta, were investigating the digestive system of the marine shipworm Psiloteredo healdi - not a true worm, but an elongated mollusc that can bore into woodwork, often of ships, by rotating its two shells. The broken-down wood and anything else encountered passes into the shipworm, where it is digested in the Gland of Deshayes (named after the French geologist Gerard Paul Deshayes, who in the 19th century first observed the gland in fossil molluscs).
It was no surprise some years ago when other researchers found that the Gland of Deshayes contained enzymes capable of breaking down the cellulose fibres in wood, yielding glucose which the shipworm uses as a source of energy. The enzymes are formed not by the mollusc itself, but from bacteria living in the gland; just as bacteria inside ruminants, such as cows and sheep, form enzymes that digest the cellulose in grass and other plants.
But the shipworm does not live on cellulose alone. It requires enzymes to break down other materials, including proteins, ingested during its boring activities. Mr Greene and his co-workers discovered that these include a protease secreted into the gland by an as yet unnamed bacterium that lives there. This protease is active and stable at temperatures between 25C and 50C, and is equally effective in attacking proteinaceous stains when used as a pre-soak or for the wash itself.
One of the most attractive properties of the newly discovered enzyme stems from its high activity in the sort of alkaline conditions found in the Gland of Deshayes.
For many years, sodium tripolyphosphate has been used in washing powders to prevent various forms of dirt from adhering to fabrics. But as it has come under increasing suspicion as a cause of the deadening of lakes and rivers by eutrophication, this chemical has been removed from commercial laundry detergents, or at least drastically reduced in concentration.
The new formulations tend to be relatively alkaline, a condition in which existing proteases are less effective. But the activity of the new shipworm proteases is not impaired in this way. The enzyme is also expected to work well in the energy-conserving cold-water detergents that are being developed.
The Peoria researchers even have a second application for their new enzyme, which they have shown can be produced relatively cheaply by growing the shipworm bacterium in nutrient broth. It is highly effective in removing the protein that accumulates on contact lenses. And, unlike existing proteases used for this purpose, it remains active in the presence of the disinfectant hydrogen peroxide. A single solution can thus be used in place of the conventional two solutions for cleansing and sterilising.
Can you imagine any funding agency in Britain these days backing a scientist who wanted to help contact-lens wearers by studying the digestive system of a so-called worm that isn't even a worm anyway?
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