title: The evolution of new enzyme function: lessons from xenobiotic metabolizing bacteria versus insecticide-resistant insects.
abstract: Here, we compare the evolutionary routes by which bacteria and insects have evolved enzymatic processes for the degradation of four classes of synthetic chemical insecticide. For insects, the selective advantage of such degradative activities is survival on exposure to the insecticide, whereas for the bacteria the advantage is simply a matter of access to additional sources of nutrients. Nevertheless, bacteria have evolved highly efficient enzymes from a wide variety of enzyme families, whereas insects have relied upon generalist esterase-, cytochrome P450- and glutathione-S-transferase-dependent detoxification systems. Moreover, the mutant insect enzymes are less efficient kinetically and less diverged in sequence from their putative ancestors than their bacterial counterparts. This presumably reflects several advantages that bacteria have over insects in the acquisition of new enzymatic functions, such as a broad biochemical repertoire from which new functions can be evolved, large population sizes, high effective mutation rates, very short generation times and access to genetic diversity through horizontal gene transfer. Both the insect and bacterial systems support recent theory proposing that new biochemical functions often evolve from 'promiscuous' activities in existing enzymes, with subsequent mutations then enhancing those activities. Study of the insect enzymes will help in resistance management, while the bacterial enzymes are potential bioremediants of insecticide residues in a range of contaminated environments.
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Robyn J
authors.initials: RJ
authors.lastname: Russell
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Colin
authors.initials: C
authors.lastname: Scott
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Jackson
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Rinku
authors.initials: R
authors.lastname: Pandey
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Gunjan
authors.initials: G
authors.lastname: Pandey
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Taylor
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Coppin
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: Jian-Wei
authors.initials: JW
authors.lastname: Liu
authors.affiliation: CSIRO Ecosystem Sciences Canberra, ACT, Australia.
authors.forename: John G
authors.initials: JG
authors.lastname: Oakeshott
keywords: carbamates; hydrolases; organochlorines; organophosphates; pyrethroids