Humanity produces and uses a lot of chemicals, such as pesticides, herbicides, etc., that find their way into the environment. These chemicals can cause undesirable environmental outcomes. Bacteria exposed to these chemicals can also rapidly evolve the ability to consume them as a source of food and energy. This is possible because bacteria evolve new enzymes that can degrade the chemical contaminants. We find bacteria that can degrade pesticides and other chemicals, then isolate and characterise the enzymes that they use to do this. We then re-engineer these enzymes as ‘bioremediants’, which can be used to clean up contaminated environments. To date we have developed bioremediants of this kind for a class of insecticides (organophosphates) and a class of herbicides (triazines).
Triazines and Organophosphates
Triazines are a family of herbicides that are widely used in broad acre cropping. At high doses triazines have been shown to impact the development of some vertebrates. Organophosphates (OPs) are insecticides used in horticulture, broad acre cropping and other agricultural systems. OPs are potent neurotoxins, affecting the nervous system of most animals leading to paralysis and death. We have developed enzymatic bioremediants for both of these classes of compound: we have isolated organisms that breakdown these pollutants, characterised the cognate enzymes, and developed and field-trialed the bioremediants (learn more here). The OP bioremediant also has potential medical applications in treating OP poisoning.
The herbicide-degrading enzyme AtzA. The three dimensional structure is shown as a ‘cartoon’ (low detail), except for the active site where the reaction occurs, for which atomic-level detail is shown.
Bacteria have evolved the ability to use pesticides as nutrients since these chemicals were introduced in the mid-twentieth century. So, pesticide degrading bacteria are excellent model systems in which to study enzyme and metabolic evolution. We have used a triazine-degrading bacterium to study: 1) enzyme neofunctionalisation (gain of a new enzymatic function), and 2) metabolic re-purposing (using existing enzymes for new jobs).
An unexpected vestigial protein complex reveals the evolutionary origins of an s-triazine catabolic enzyme. Esquirol L, Peat TS, Wilding M, Liu JW, French NG, Hartley CJ, Onagi H, Nebl T, Easton CJ, Newman J & Scott C. J. Biol. Chem – Editor’s Pick (Old enzymes versus new herbicides).
Efficacy of an organophosphorus hydrolase enzyme (OpdA) in human serum and minipig models of organophosphorus insecticide poisoning. Eddleston M, Clutton ER, Taylor M, Thompson A, Worek F, John H, Thiermann H & Scott C. Clinical Toxicol. DOI: 10.1080/15563650.2019.1655149.
Bacterial catabolism of s-triazine herbicides: biochemistry, evolution and application. Esquirol L, Peat TS, Sugrue E, Balotra S, Rottet S, Warden AC, Wilding M, Hartley CJ, Jackson CJ, Newman J & Scott C. Adv. Microbial Physiol. 76
Free-Enzyme Bioremediation of Pesticides: A Case Study for the Enzymatic Remediation of Organophosphorous Insecticide Residues. Scott C, Begley C, Taylor MJ, Pandey G, Momiroski V, French NG, Brearley C, Kotsonis SE, Selleck MJ, Carino FA, Bajet CM, Clarke C, Oakeshott JG, Russell RJ. In Pesticide Mitigation Strategies for Surface Water Quality, Chapter 11 pp 155-174. ACS Symposium Series 1075