UWB Crest

Bangor Biodegradation Group

General Overview

Microbes as Biodegraders

Microbes (bacteria and fungi) found in natural waters and soils have between them a very broad ability to utilise (catabolise) virtually all naturally-occurring compounds as their sources of carbon and energy, thus recycling the fixed, organic carbon back into harmless biomass and carbon dioxide. The breadth of this catabolic ability of microbes far exceeds the hugely more limited abilities of higher organisms which can only use a relatively small range of compounds as 'foodstuffs'.  This capability of microbes has evolved over 3 billion years of the planets history and is responsible for the balance between photosynthesis (by plants and algae), fixing carbon dioxide into biomass, and respiration (by animals and bacteria), converting organic compounds back to carbon dioxide by oxidation. This allows the limited amount of carbon available for life to be recycled (the Carbon Cycle). In more recent times, microbial degadation has been channelled into technologies for the degradation of natural household wastes by the use of cess-pits, septic tanks and sewage works.
 
Recent advances in genetics and molecular biology in the last 20-30 years has shown that bacteria are genetically extremely adaptable and, in addition to the advantage due to their rapid growth rates, have a range of mechanisms which enable them to adapt to new environments. The advent of modern chemical industry has resulted in the release into the environment of huge amounts of novel organic compounds, as industrial by-products, as pesticides, as other agrochemicals etc. Bacteria appear able to adapt their pre-existing catabolic breadth to enable them to attack and degrade many of these novel xenobiotic (= foreign to biology) compounds.

This has led to the possibility of using mixtures of bacteria (consortia) or even cultures of single organisms to either clean-up polluted environments or to degrade potential pollutants at source and before their release into the environment. This has led to an entire new industry, that of bioremediation, whose role is to optimise conditions for natural bacteria to degrade. However although bacteria are very useful in this respect, they are not a universal solution to pollution problems. Some compounds with complex structures are highly recalcitrant to biodegradation, and some sites have become so polluted with toxic mixtures of both organic and inorganic compounds, that nothing can live there. In these instances, chemical or physical processes for clean-up still have to be utilised.

Biodegradation research has two spin-offs:
(1) Many of the enzymes used in the pathways for degrading unusual substrates catalyse novel reactions often non-specifically and have potential use as biocatlysts in industry for the production of novel fine chemicals which are otherwise difficult to synthesise.
(2) An understanding of the pathways and their genes can lead to the use of recombinant strains carrying genetically hybrid pathways (i.e. made up from genes from different bacterial strains) which can degrade compounds which are otherwise resistant to natural bacteria.

Some Basic Reading

Brock Biology of microorganisms by Madigan, Martinko & Parker (9th edition), Prentice Hall.
     Carbon cycle:  pp.676-677
     Sewage and wastewater treatment:    pp.416-420
     Biodegradation of petroleum & xenobiotics:  pp.696-703

Pollution Science by Pepper, Gerba & Brusseau, Academic Press
    In particular Part 2 (Chaps. 8-11), Monitoring and remediation of environmental pollution and  Chap. 20, Municipal waste and drinking water.

Microbial control of pollution, Society for General Microbiology Symposia 48 (1992)
     Bioremediation of oil spills, with particular reference to the spill from the Exxon Valdez by R.C.Prince pp.19-34  and other chapters.

Biodegradation and Bioremediation by Martin Alexander, Academic Press
     See Chapter 15 for some of the engineering solutions to bioremediation.

Scientific American article
     Soiled shores,  October 1999, pp.80-94. A general article covering the problem of marine oil spills.

Silent Spring by Rachel Carson
     A classic book first published in 1962 and now reprinted as a Penguin paperback, which was a major influence on the international awareness in the cumulative effects of pollution through the indiscriminate use of non-biodegradable xenobiotics in the environment. Essential reading for the historically-aware environmental biologist.