Kinetic and sequence-structure-function analysis of LinB enzyme variants with β- and δ-hexachlorocyclohexane.

Organochlorine insecticide hexachlorocyclohexane (HCH) has recently been classified as a 'Persistent Organic pollutant' by the Stockholm Convention. The LinB haloalkane dehalogenase is a key upstream enzyme in the recently evolved Lin pathway for the catabolism of HCH in bacteria. Here we report a sequence-structure-function analysis of ten naturally occurring and thirteen synthetic mutants of LinB.

Functional screening of enzymes and bacteria for the dechlorination of hexachlorocyclohexane by a high-throughput colorimetric assay.

Two distinct microbial dehalogenases are involved in the first steps of degradation of hexachlorocyclohexane (HCH) isomers. The enzymes, LinA and LinB, catalyze dehydrochlorination and dechlorination reactions of HCH respectively, each with distinct isomer specificities. The two enzymes hold great promise for use in the bioremediation of HCH residues in contaminated soils, although their kinetics and isomer specificities are currently limiting.

Cloning of a novel 6-chloronicotinic acid chlorohydrolase from the newly isolated 6-chloronicotinic acid mineralizing Bradyrhizobiaceae strain SG-6C.

A 6-chloronicotinic acid mineralizing bacterium was isolated from enrichment cultures originating from imidacloprid-contaminated soil samples. This Bradyrhizobiaceae, designated strain SG-6C, hydrolytically dechlorinated 6-chloronicotinic acid to 6-hydroxynicotinic acid, which was then further metabolised via the nicotinic acid pathway. This metabolic pathway was confirmed by growth and resting cell assays using HPLC and LC-MS studies.

Kinetic and sequence-structure-function analysis of known LinA variants with different hexachlorocyclohexane isomers.

Background: Here we report specific activities of all seven naturally occurring LinA variants towards three different isomers, α, γ and δ, of a priority persistent pollutant, hexachlorocyclohexane (HCH). Sequence-structure-function differences contributing to the differences in their stereospecificity for α-, γ-, and δ-HCH and enantiospecificity for (+)- and (-)-α -HCH are also discussed.

Methodology/principal Findings: Enzyme kinetic studies were performed with purified LinA variants.

Genome sequence of the newly isolated chemolithoautotrophic Bradyrhizobiaceae strain SG-6C.

Strain SG-6C (DSM 23264, CCM 7827) is a chemolithoautotrophic bacterium of the family Bradyrhizobiaceae. It can also grow heterotrophically under appropriate environmental conditions. Here we report the annotated genome sequence of this strain in a single 4.

The evolution of new enzyme function: lessons from xenobiotic metabolizing bacteria versus insecticide-resistant insects.

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.

Degradation of dichloroaniline isomers by a newly isolated strain, Bacillus megaterium IMT21.

An efficient 3,4-dichloroaniline (3,4-DCA)-mineralizing bacterium has been isolated from enrichment cultures originating from a soil sample with a history of repeated exposure to diuron, a major metabolite of which is 3,4-DCA. This bacterium, Bacillus megaterium IMT21, also mineralized 2,3-, 2,4-, 2,5- and 3,5-DCA as sole sources of carbon and energy. These five DCA isomers were degraded via two different routes.

Competing S(N)2 and E2 reaction pathways for hexachlorocyclohexane degradation in the gas phase, solution and enzymes.

Quantum chemistry calculations have been used alongside experimental kinetic analysis to investigate the competition between S(N)2 and E2 mechanisms for the dechlorination of hexachlorocyclohexane isomers, revealing that enzyme specificity reflects the intrinsic reactivity of the various isomers.

Biochemistry of microbial degradation of hexachlorocyclohexane and prospects for bioremediation.

Lindane, the gamma-isomer of hexachlorocyclohexane (HCH), is a potent insecticide. Purified lindane or unpurified mixtures of this and alpha-, beta-, and delta-isomers of HCH were widely used as commercial insecticides in the last half of the 20th century. Large dumps of unused HCH isomers now constitute a major hazard because of their long residence times in soil and high nontarget toxicities.

The enzymatic basis for pesticide bioremediation.

Enzymes are central to the biology of many pesticides, influencing their modes of action, environmental fates and mechanisms of target species resistance. Since the introduction of synthetic xenobiotic pesticides, enzymes responsible for pesticide turnover have evolved rapidly, in both the target organisms and incidentally exposed biota. Such enzymes are a source of significant biotechnological potential and form the basis of several bioremediation strategies intended to reduce the environmental impacts of pesticide residues.