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Hiding in the midst of trash are valuable bacteria that can degrade environmental toxins. (Photo: Avinash Kumar for Unsplash)

Detoxifiers from the landfill

June 18, 2021 | Annette Ryser

Bacteria from an Indian landfill could help eliminate contaminated chemicals. The focus is on pesticides such as lindane or brominated flame retardants, which accumulate in nature and in food chains. Researchers at Eawag and Empa used these bacteria to generate enzymes that can break down these dangerous chemicals.

Can we recapture or detoxify the chemical waste of past generations? Microbiologist Hans Peter Kohler from the aquatic research institute Eawag and Empa chemist Norbert Heeb, together with researchers from the Zurich University of Applied Sciences (ZHAW) and two Indian institutes, put the question to the test.

Read the full article on this topic on the Empa website: Detoxifiers from the landfill

Cover picture: Avinash Kumar für Unsplash

Cooperations

  • Empa
  • Zurich University of Applied Sciences (ZHAW)

Original publication

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      originalId => protected22027 (integer)
      authors => protected'Heeb, N. V.; Hubeli, J.; Fleischmann, T.; Lienemann,&nbs
         p;P.; Nayyar, N.; Lal, R.; Kohler, H. P. E.' (144 chars)
      title => protected'Transformation of ε-HBCD with the <em>Sphingobium Indicum</em> enzymes LinA
         1, LinA2 and LinATM, a triple mutant of LinA2' (121 chars)
      journal => protected'Chemosphere' (11 chars)
      year => protected2021 (integer)
      volume => protected267 (integer)
      issue => protected'' (0 chars)
      startpage => protected'129217 (12 pp.)' (15 chars)
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      description => protected'Hexabromocyclododecanes (HBCDs) were used as flame-retardants until their ba
         n in 2013. Among the 16 stereoisomers known, ε-HBCD has the highest symmetr
         y. This makes ε-HBCD an interesting substrate to study the selectivity of b
         iotransformations. We expressed three LinA dehydrohalogenase enzymes in <em>
         E. coli</em> bacteria, two wild-type, originating from <em>Sphingobium indic
         um</em> B90A bacteria and LinATM, a triple mutant of LinA2, with mutations o
         f L96C, F113Y and T133 M. These enzymes are involved in the hexachlorocycloh
         exane (HCH) metabolism, specifically of the insecticide γ-HCH (Lindane). We
          studied the reactivity of those eight HBCD stereoisomers found in technical
          HBCD. Furthermore, we compared kinetics and selectivity of these LinA varia
         nts with respect to ε-HBCD. LC-MS data indicate that all enzymes converted 
         ε-HBCD to pentabromocyclododecenes (PBCDens). Transformations followed Mich
         aelis-Menten kinetics. Rate constants k<sub>cat</sub> and enzyme specificiti
         es k<sub>cat</sub>/K<sub>M</sub> indicate that ε-HBCD conversion was fastes
         t and most specific with LinA2. Only one PBCDen stereoisomer was formed by L
         inA2, while LinA1 and LinATM produced mixtures of two PBCDE enantiomers at t
         
         
          assume that 1E,5S,6R,9S,10R-PBCDen is the ε-HBCD transformation product fr
         om LinA2. Implementing three amino acids of the LinA1 substrate-binding site
          into LinA2 resulted in a triple mutant with similar kinetics and product sp
         ecificity like LinA1. Thus, point-directed mutagenesis is an interesting too
         l to modify the substrate- and product-specificity of LinA enzymes and enlar
         ge their scope to metabolize other halogenated persistent organic pollutants
          regulated under the Stockholm Convention.' (1866 chars)
      serialnumber => protected'0045-6535' (9 chars)
      doi => protected'10.1016/j.chemosphere.2020.129217' (33 chars)
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Transformation of ε-HBCD with the Sphingobium Indicum enzymes LinA1, LinA2 and LinATM, a triple mutant of LinA2

Hexabromocyclododecanes (HBCDs) were used as flame-retardants until their ban in 2013. Among the 16 stereoisomers known, ε-HBCD has the highest symmetry. This makes ε-HBCD an interesting substrate to study the selectivity of biotransformations. We expressed three LinA dehydrohalogenase enzymes in E. coli bacteria, two wild-type, originating from Sphingobium indicum B90A bacteria and LinATM, a triple mutant of LinA2, with mutations of L96C, F113Y and T133 M. These enzymes are involved in the hexachlorocyclohexane (HCH) metabolism, specifically of the insecticide γ-HCH (Lindane). We studied the reactivity of those eight HBCD stereoisomers found in technical HBCD. Furthermore, we compared kinetics and selectivity of these LinA variants with respect to ε-HBCD. LC-MS data indicate that all enzymes converted ε-HBCD to pentabromocyclododecenes (PBCDens). Transformations followed Michaelis-Menten kinetics. Rate constants kcat and enzyme specificities kcat/KM indicate that ε-HBCD conversion was fastest and most specific with LinA2. Only one PBCDen stereoisomer was formed by LinA2, while LinA1 and LinATM produced mixtures of two PBCDE enantiomers at three times lower rates than LinA2. In analogy to the biotransformation of (−)β-HBCD, with selective conversion of dibromides in R-S-configuration, we assume that 1E,5S,6R,9S,10R-PBCDen is the ε-HBCD transformation product from LinA2. Implementing three amino acids of the LinA1 substrate-binding site into LinA2 resulted in a triple mutant with similar kinetics and product specificity like LinA1. Thus, point-directed mutagenesis is an interesting tool to modify the substrate- and product-specificity of LinA enzymes and enlarge their scope to metabolize other halogenated persistent organic pollutants regulated under the Stockholm Convention.
Heeb, N. V.; Hubeli, J.; Fleischmann, T.; Lienemann, P.; Nayyar, N.; Lal, R.; Kohler, H. P. E. (2021) Transformation of ε-HBCD with the Sphingobium Indicum enzymes LinA1, LinA2 and LinATM, a triple mutant of LinA2, Chemosphere, 267, 129217 (12 pp.), doi:10.1016/j.chemosphere.2020.129217, Institutional Repository
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