Science / Microbe of the Month: Nature's cure for global pollution: Some bacteria can help to break down chemicals that cause damage to the environment, says Bernard Dixon
Monday 17 May 1993
One reason for Gaia's mixed reception is that the theory is capable of being turned to different and even conflicting ends. It may, by highlighting the interrelatedness of the countless components of the biosphere and their links with the physical world, make us more aware of the folly of treating the environment as a bottomless sink for effluents and other pollutants. Alternatively, Gaia's resourcefulness and flexibility may suggest that she can cope, especially in the long-term, with any chemical or physical insults generated by industrial society.
Methylosinus trichosporium is a case in point. One of a group of naturally occurring microbes that live by oxidising methane into methanol, this tiny bacterium has been attracting keen interest recently because it has an additional talent that previously went unnoticed. It can break down certain products of the chemical industry that would otherwise contribute to the depletion of the Earth's protective ozone layer.
Once again, the discovery of a hitherto unknown skill possessed by one of the planet's myriad life-forms has emphasised both our ignorance of natural processes and our potential fecklessness in destroying their benefits through our clumsy interference with the environment. At the same time, we may be reassured by the knowledge that that M. trichosporium, and possibly other widely disseminated microbes too, can cope with a particular range of pollutants. But reassurance can quickly turn to complacency.
The gases known as chlorofluorocarbons (CFCs) have been used since the Thirties in refrigerators and air-conditioning equipment and more recently as aerosol propellants and in foam packaging. Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) have been developed over the past 10 years as more environmentally friendly alternatives. Though sometimes criticised for contributing to the Western world's extravagance with energy and materials and for destroying the ozone layer, CFCs have also brought benefits - for example, in helping to preserve life-saving vaccines so that they can be transported to remote parts of the world.
Following the Montreal protocol of 1987, CFCs should be phased out by the end of the century. Two groups of possible alternatives are HCFCs, which are substantially less destructive of the ozone layer than CFCs, and HCFs, which do not threaten the ozone shield at all - though they are under suspicion as contributing (like carbon dioxide) to global warming.
There is another important difference between HFCs and HCFCs, which could commend them as ecologically acceptable alternatives. CFCs are highly persistent, with virtually no known microbial or other biological processes by which they might be broken down. Chemists have calculated that most of the total amount of these gases released into the atmosphere over the past six decades is still there. A recalcitrant burden of pollution such as this would be highly unlikely if HFCs and HCFCs were to be used instead.
The reason for this, as reported in Bio/Technology by Dr Mary DeFlaun and colleagues at Envirogen Inc in Lawrenceville, New Jersey, is that these potential alternatives are subject to microbial attack.
Dr DeFlaun and her associates were prompted to study M. trichosporium by the discovery three years ago that it contains enzymes capable of breaking down chemicals with a similar molecular structure to CFCs. By incubating the bacterium with three different HFCs and five different HCFCs, they found that it degraded one of the former and three of the latter.
Although these successes are less than total, their major significance is in demonstrating that the potential replacements for CFCs can be broken down at all, and in suggesting that M. trichosporium and other methane oxidisers may provide a natural mechanism by which HFCs and HCFCs can be rendered safe.
M. trichosporium is just one representative (and the Envirogen researchers studied only a single strain) of a group of bacteria that are widespread in nature. Known to be very common inhabitants of the soil, lakes, swamps, aquifers, rice paddies and other environments in contact with the atmosphere, these methane oxidisers, which include Methylocystis and Methylobacter, have been comparatively little studied until recent years. It is entirely possible therefore that together they can meet the task of breaking down a wide range of HFCs and HCFCs.
Dr DeFlaun and her colleagues are confident that microbes such as M. trichosporium might be harnessed to dispose of the refrigerants in certain situations. They might, for example, be used to prevent emissions of HFCs and HCFCs at production and recycling plants, just as other microbes are exploited to deal with other unwanted effluents. But the major issue is whether regulatory authorities should sanction the widespread use of beneficial products when, as may well be true in this case, microbes in soil and water are more than capable of preventing them from accumulating in the environment.
Should Gaia not provide unambiguous answers on questions of this kind?
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