Published online 18 September 2000 | Nature | doi:10.1038/news000921-6


Hair razing

Biotechnologists searching for new medicines should shave, says David Adam.

Biotechnologists searching for new medicines should take a tip from Olympic swimmers and remove excess hair, new research suggests. Root hairs make it difficult to mix and grow large-scale plant cell cultures used to produce antibiotics and other important natural products. Removing root hair can more than double the growth rate and boost yields, chemical engineers in America now show.

So-called 'hairy-root' cultures of plant cells have been popular with plant researchers for about a decade. They are produced by genetically transforming plants by using bacteria genes, making the whole plant grow as a root.

This is useful because roots produce greater amounts of defensive chemicals such as antibiotics, which are often used for human medicine. Many researchers believe that such cultures will offer an environmentally friendly way of finding and producing new drugs.

But, as their name implies, these modified roots could do with a shave. Thin hairs -- needed to grab nutrients from soil -- cover their surface. Liquid cultures make such hair redundant because essential elements are constantly supplied. In fact the hairs are a positive drag -- blocking fluid flow and limiting oxygen availability -- Julie Bordonaro and Wayne Curtis at Pennsylvania State University in University Park now show.

The hairs are blamed for poor performance of 'scaled-up' reactors: experiments that work perfectly in small flasks go wrong when they are transferred to bigger tanks. But previous attempts to clarify this could only compare different plant species with varying amounts of root hair.

Bordonaro and Curtis have now directly compared hairy and hairless roots from the same plant, they will soon report in the journal Biotechnology and Bioengineering1. Their conclusion: root hairs are detrimental to growth in a liquid environment.

Treating cultures of the plant Hyoscyamus muticus (a source for motion-sickness drugs) with a dye chemical called pyrene butyric acid (PBA) removes hair without affecting growth or root shape, the duo say. This allowed them to compare hairy and hairless roots by growing both cultures in identical 15-litre 'bioreactors', in which oxygen and nutrients are mixed around to help growth.

As the root cultures grow, their tangled shapes make mixing more difficult. But hairs make the situation worse, the duo report. After three weeks, "the mixing time of the hairy culture was 29 times longer than that of the hairless culture," Curtis says. And the growth rate of the hairless culture was up to 2.4 times higher, bringing about a 48% increase in plant 'biomass' -- the raw material for drugs research.

The hairless cultures grow better because air and liquid can flow past roots much easier, Curtis says. This prevents areas of 'stagnation' within bioreactors, which is crucial for reliable growth in the large tanks needed for commercial production.

Many sports scientists scoff at swimmers shaving their bodies -- suggesting that the reduced drag is unnoticeable and the only benefit is increased confidence. But when one swimmer does it, others copy.

Copying the hairless root technique with other useful plants could be trickier: Bordonaro and Curtis stumbled across the PBA treatment while using it in oxygen-sensing experiments. Similar hair-removal techniques for other plants could be harder to find. 

  • References

    1. Bordonaro,J. L. & Curtis, W. R. Inhibitory role of root hairs on transport within root culture bioreactors. Biotechnology and Bioengineering 70, 176 - 186 2000. | Article | PubMed | ISI | ChemPort |