Methanotrophs for Clean-Up of Polluted Aquifers

Abstract

Aquifers are vital reserves of drinking water which are under threat from pollution. Particular problems are posed by chlorinated compounds such as pesticides and solvents which native microbial populations are unable to degrade. Pump and treat regimes have proved unsuccessful since pollutants remain adsorbed to sediments but a possible solution is the use of introduced microorganisms to degrade pollutants in-situ. It is suggested that methanotrophs may be suitable candidates. Methanotrophs have an extraordinary range of degradative powers due to the non-specificity of their methane mono-oxygenase enzyme. We have shown that Methylosinus trichosporium OB3b is capable of degrading many common chlorinated pollutants co-metabolically when it is grown in a copper-depleted, oxygen-rich medium at neutral pH. In the subsurface however, such conditions do not exist and cultures grown in a medium made with untreated Cambridge aquifer water have a reduced range of degradative powers compared to similar cells grown in a medium made with distilled water. This means that to use methanotrophs for aquifer clean-up, the cells may need to be cultured above ground in ideal conditions and then introduced by some method of injection or infiltration. This may be possible because the degradative reactions are not coupled to growth and Methylosinus trichosporium OB3b cells maintain pollutant degrading ability up to 19 days after they have stopped growing. A suspension of these cells may thus be treated as a biocatalyst.