BIOREMEDIATION WITH ENZYMES

In the last few years, enzymatic bioremediation has risen as an attractive alternative to further support the bio-treatment techniques currently available, since enzymes are more simple systems than a whole organism. Most xenobiotics can be submitted to enzymatic bioremediation, e.g. polycyclic aromatic hydrocarbons (PAHs), polynitrated aromatic compounds , pesticides such as organochlorine insecticides , bleach-plant effluents, synthetic dyes, polymers and wood preservatives (creosote, pentachlorophenol) . 

It is just a matter of searching the microorganisms capable to feed with a particular pollutant , and afterwards focusing the effort in finding out which enzyme(s) is(are) behind this behaviour. Historically, the most studied enzymes in bioremediation are bacterial mono- or di-oxygenases, reductases, dehalogenases, citochrome P450 monoxygenases, enzymes involved in lignin-metabolism (laccases, lignin peroxidases and manganese peroxidases from white-rot fungi), and bacterial phosphotriesterases. Moreover, new developments in the design and application of enzymatic cocktails for biotreatment of waste-waters have recently emerged due to the effort of many companies and administrations. From an environmental point of view, the use of enzymes instead of chemicals or microorganisms undoubtedly presents some advantages:

  • the biotransformation does not generate toxic side-products, and after the treatment, the enzymes are digested on-site by the indigenous microorganisms
  • the requirement of enhancing the bio-availability by the introduction of organic cosolvents or surfactants is much more feasible from an enzymatic point of view rather than using whole cells
  • the possibilities to produce enzymes in a higher scale with enhanced stability and/or activity and at a lower cost by recombinant-DNA technology.

When performing enzymatic bioremediation, it is imperative that the enzyme is kept optimally during operational conditions. This requires cheap produced enzymes (i.e. heterologous expression) with high substrate affinity (Km in the micromolar range), supporting thousands of product turnovers. At the same time enzymes should display robustness under an array of external factors and low dependency on expensive redox cofactors (i.e. NAD(P)H), which would be prohibitive in a commercial setting.