title: Bacterial production of organic acids enhances H2O2-dependent iodide oxidation.
abstract: To develop an understanding of the role that microorganisms play in the transport of (129)I in soil-water systems, bacteria isolated from subsurface sediments were assessed for iodide oxidizing activity. Spent liquid medium from 27/84 bacterial cultures enhanced iodide oxidation 2-10 fold in the presence of H(2)O(2). Organic acids secreted by the bacteria were found to enhance iodide oxidation by (1) lowering the pH of the spent medium, and (2) reacting with H(2)O(2) to form peroxy carboxylic acids, which are extremely strong oxidizing agents. H(2)O(2)-dependent iodide oxidation increased exponentially from 8.4 to 825.9 μM with decreasing pH from 9 to 4. Organic acids with ≥2 carboxy groups enhanced H(2)O(2)-dependent iodide oxidation (1.5-15-fold) as a function of increasing pH above pH 6.0, but had no effect at pH ≤ 5.0. The results indicate that as pH decreases (≤5.0), increasing H(2)O(2) hydrolysis is the driving force behind iodide oxidation. However, at pH ≥ 6.0, spontaneous decomposition of peroxy carboxylic acids, generated from H(2)O(2) and organic acids, contributes significantly to iodide oxidation. The results reveal an indirect microbial mechanism, organic acid secretion coupled to H(2)O(2) production, that could enhance iodide oxidation and organo-iodine formation in soils and sediments.
authors.affiliation: Department of Marine Sciences, Texas A&M University, Galveston, Texas 77551, USA. original@tamu.edu
authors.forename: Hsiu-Ping
authors.initials: HP
authors.lastname: Li
authors.forename: Chris M
authors.initials: CM
authors.lastname: Yeager
authors.forename: Robin
authors.initials: R
authors.lastname: Brinkmeyer
authors.forename: Saijin
authors.initials: S
authors.lastname: Zhang
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Ho
authors.forename: Chen
authors.initials: C
authors.lastname: Xu
authors.forename: Whitney L
authors.initials: WL
authors.lastname: Jones
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Schwehr
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Otosaka
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Roberts
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaplan
authors.forename: Peter H
authors.initials: PH
authors.lastname: Santschi
mesh_terms: D001419:Bacteria / Q000378:metabolism; D002264:Carboxylic Acids / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D007454:Iodides / Q000737:chemistry*; D007457:Iodine Radioisotopes / Q000737:chemistry; D010084:Oxidation-Reduction; D012988:Soil Microbiology; D012990:Soil Pollutants, Radioactive / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D007454:Iodides; D007457:Iodine Radioisotopes; D012990:Soil Pollutants, Radioactive; D006861:Hydrogen Peroxide