title: Formation of chloroform and tetrachloroethene by Sinorhizobium meliloti strain 1021.
abstract: The mechanisms and organisms involved in the natural formation of volatile organohalogen compounds (VOX) are largely unknown. We provide evidence that the common and widespread soil bacterium Sinorhizobium meliloti strain 1021 is capable of producing up to 3338·6 ± 327·8 ng l(-1) headspace volume of chloroform (CHCl3 ) and 807·8 ± 13·5 ng l(-1)  headspace volume of tetrachloroethene (C2 Cl4 ) within 1 h when grown in soil extract medium. Biotic VOX formation has been suggested to be linked to the activity of halogenating enzymes such as haloperoxidases. We tested if the observed VOX formation by S. meliloti can be attributed to one of its chloroperoxidases (Smc01944) that is highly expressed in the presence of H2 O2. However, addition of 10 mmol l(-1) H2 O2 to the S. meliloti cultures decreased VOX formation by 52% for chloroform and 25% for tetrachloroethene, while viable cell numbers decreased by 23%. Interestingly, smc01944 gene expression increased 450-fold. The quantification of extracellular chlorination activity in cell suspension experiments did not provide evidence for a role of S. meliloti chloroperoxidases in the observed VOX formation. This suggests that a momentarily unknown mechanism which requires no H2 O2 might be responsible for the VOX formation by S. meliloti. Regardless of the underlying mechanism our results suggest that the soil bacterium S. meliloti might be an important source of VOX in soils.
  
  
  CONCLUSIONS
  Volatile organohalogen compounds (VOX) strongly influence atmospheric chemistry and Earth's climate. Besides anthropogenic emissions they are naturally produced by either abiotic or biotic pathways in various environments. Particularly in soils, microbial processes drive the natural halogen cycle but the direct link to microbial VOX formation has not been studied in detail yet. In this study we provide evidence that the common and widespread soil bacterium Sinorhizobium meliloti strain 1021 forms chloroform and tetrachloroethene. The potential contribution of S. meliloti to soil VOX release could significantly influence soil and atmospheric chemistry.
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Weigold
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Ruecker
authors.affiliation: Instrumental Analytical Chemistry, Faculty of Chemistry, University of Duisburg-Essen, Essen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Jochmann
authors.affiliation: Instrumental Analytical Chemistry, Faculty of Chemistry, University of Duisburg-Essen, Essen, Germany.
authors.forename: X L
authors.initials: XL
authors.lastname: Osorio Barajas
authors.affiliation: Environmental Analytical Chemistry, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Lege
authors.affiliation: Environmental Analytical Chemistry, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Zwiener
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kappler
authors.affiliation: Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany.|Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, MN, USA.|BioTechnology Institute, University of Minnesota, Minneapolis, MN, USA.
authors.forename: S
authors.initials: S
authors.lastname: Behrens
mesh_terms: D002711:Chloride Peroxidase / Q000378:metabolism*; D002725:Chloroform / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism*; D012987:Soil; D012988:Soil Microbiology; D013750:Tetrachloroethylene / Q000378:metabolism*; D055549:Volatile Organic Compounds / Q000378:metabolism*
chemical_list: D012987:Soil; D055549:Volatile Organic Compounds; D002725:Chloroform; D006861:Hydrogen Peroxide; D002711:Chloride Peroxidase; D013750:Tetrachloroethylene
keywords: Sinorhizobium meliloti; Smc01944; biotic halogenation; chloroform; chloroperoxidases; tetrachloroethene; volatile organohalogen compounds