Self-cleansing power

A potent cocktail of microbes could help to clean the desert areas of Kuwait that were badly polluted by damaged oil wells during the Gulf war. Bernard Dixon reports
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Microbes are our planet's great scavengers - breaking down dead animal and plant tissues in the soil, and serving as the tireless workhorses of sewage disposal. Now comes news that they hold the solution to one of the worst environmental disasters ever known - the pollution of large tracts of the Kuwaiti desert with oil during the Gulf war of 1991. Naser Sorkhoh and colleagues at Kuwait University in Safat, Kuwait, have found a "unique natural microbial cocktail" which they believe can be used to clean up huge tracts of contaminated sand.

Some 700 oil wells in the desert were damaged in one way or another during the conflict. In consequence, oil gushed freely into the sand, day after day, for about seven months. It polluted large areas of the desert, forming so-called oil lakes. Although much of the oil has since been pumped away, much remains in the sand, to a depth of 30cms or more.

Although it received less publicity, the pollution of the land was more severe even than that of the sea. At the best of times, the Arabian Gulf receives more than its share of oil pollution. Accidental spills, leaks and illegal dumping between them account for an estimated 160,000 tons of the stuff per annum. During the occupation of Kuwait, however, this burden was eclipsed by the largest single incident of oil pollution to have taken place anywhere in the world. On 19 January 1990, Iraqi forces released some 500,000 tons of crude oil from the Mina Al-Ahmadi terminal. The thick, black oil drifted southwards and settled along the Kuwaiti and Saudi Arabian coasts, killing all living creatures in its path.

Yet within a few months, Naser Sorkhoh and his collaborators reported that one form of life had returned. They found, on top of the oil in many places, blue-green mats composed of filamentous cyanobacteria. These are bacteria which, like green plants, can harness the sun's energy in the process of photosynthesis. Normal inhabitants of the region, their numbers were usually kept in check because various marine animals "grazed" on them. But these animals had been eliminated by the oil, allowing the cyanobacteria to flourish. As they did so, they produced mucilage, embedded within which were other types of bacteria that were able to break down the oil.

Reporting the hitherto-unknown, scum-like microbial mats in Nature two years ago, the Kuwait University scientists described them as the first signs of self-cleansing in the polluted region. Since that time, they have continued to monitor the microbial activity in the blue-green mats, and have charted the contribution made by the microbes to the gradual recovery of the horrendously contaminated Kuwaiti and Saudi coastline.

Armed with that knowledge, Naser Sorkhoh and his co-workers have now evaluated the potential application of the same bacteria in coping with what may be a longer-lasting environmental consequence of the Gulf war - pollution of the Kuwaiti desert. Here, in contrast to the sea, there is no self-cleansing.

Perhaps the microbes in the blue-green mats might be used to attack the oil in the sand too? Sorkhoh and his colleagues decided to investigate this type of "bioremediation". They collected fresh mats from the oily coasts of Al-Khiran in Kuwait and Jubail in Saudi Arabia, freed them from adhering oil, suspended them in sea-water and homogenised the mixture in a blender. Then they added portions of the mixture to oily desert sand (which they had already confirmed did not contain any microbes capable of attacking the oil). They sealed the samples in glass dishes and left them at room temperature for various periods of time.

The results show that the mats do indeed carry a potent cocktail of oil- degrading microbes - about a million of them in each gram of fresh mat. Moreover, those added to the contaminated sand grew rapidly, the population reaching some 1,000-10,000 times the original number after 18 to 20 weeks. The predominant bacterium was Rhodococcus, though others included Arthrobacter, Bacillus and Pseudomonas.

The make-up of the population shifted as certain fractions of oil were broken down and the initially dominant strains were replaced by those capable of degrading the remaining fractions. Depending on the original concentration, about 50 per cent of the oil had gone after 10 to 20 weeks.

Just as impressive as the scale of the reduction in oil was the ease with which the microbes, introduced from the mats into the oily sand, proliferated in their new environment. This was neither guaranteed nor predictable. Research groups adopting a similar strategy to deal with other pollutants in the past have often been disappointed when they have added to contaminated soil microbes known to attack a particular chemical in the test-tube. Sometimes, the new microbes have failed to deal with the pollutant simply because they failed to grow vigorously enough in competition with those already present in the soil.

Reporting their results in this month's Journal of Applied Bacteriology, Sorkhoh and his collaborators conclude: "Cyan-obacterial mats currently covering oil sediments along the Arabian Gulf contain a cocktail of oil- utilising micro-organisms that can be valuable in bioremediating the oil- polluted desert areas of Kuwait and other Gulf states." They now plan to test their approach on a larger scale, spraying the scavenging bacteria over the polluted desert.

They also point out that their microbial mixture, being indigenous to the region, is probably superior to any bacterial cocktail imported from elsewhere. There is now widespread interest in the idea of tailor-making microbes for bioremediation - using genetic engineering to perfect strains that are especially powerful in breaking down noxious chemicals in settings such as abandoned gas works.

In this instance, the glamour of genetic engineering may be inappropriate. Judging by the results of the Kuwait experiment - and indeed on the basis of sound ecological principles - it might well be wiser to harness microbial skills that have evolved in the very region where they are now so sorely needed.