@misc{oai:niigata-u.repo.nii.ac.jp:00005340,
 author = {Guan, Ling},
 month = {Mar},
 note = {Chemical warfare weapons containing aromatic arsenicals, such as CLARK I (diphenylcyanoarsine), and CLARK Ⅱ (diphenylchloroarsnie), were produced during the World wars. Thereafter, they were discarded in several parts of Europe, China, Japan and other countries, remaining potential leakage of aromatic arsenicals to the conjunct environment. Diphenylarsinic acid (DPAA) is often found as one of the major degradation products around the dumped sites, since the compound is easily produced from CLARK I and CLARK Ⅱ via hydrolysis and oxidation. Many studies have reported environmental transfonmation of DPAA under aerobic conditions. However, ariaerobic transformation of DPAA has not yet been explored well. The objectives of this study were to investigate, 1) the effects of DPAA on anaerobic soil microbial diversity; 2) the enhancement of DPAA transfonmation under sulfate-reducing conditions; and 3) the DPAA-transfonning microorganisms in anaerobic DPAA-contaminated soil. We conducted model experiments using anaerobic soil cultures contaminated with DPAA. The first chapter of the thesis presents occurrence of arsenic contamination in the world, toxicity of arsenicals and impacts of arsenicals on microbial diversity based on a detailed literature survey and describes the objective of this study. In Chapter Ⅱ, the effects of DPAA contamination on soil bacterial and archaeal community structures under anaerobic conditions were examined using molecular ecological analysis after incubation of soil cultures. DPAA in the anaerobic soil cultures prepared with a paddy soil (Shindori soil) decreased due to microbiological activity. Addition of rice straw partially enhanced the extent of DPAA degradation. Inorganic arsenic acid, phenylarsonic acid and an unknown arsenical species were detected as the transformation products using LC-ICPMS. The 16S rDNA-targeted PCR-DGGE fingerprinting for bacterial community analysis revealed that anaerobic bacterial and archaeal species, including Clostridium and Methanosarcina, became abundant in the incubated soil within a week. In the soil cultures incubated with DPAA, while a few bacterial bands found on the DGGE gels disappeared or became weaker, most of the bands showed no significant changes. Addition of DPAA had little effect on archaeal DGGE band patterns., These findings suggest that, even though DPAA may have a direct effect on some abundant bacterial species, overall bacterial and archaeal community structures under the anaerobic soil conditions tended to be stable regardless of DPAA contamination. The next Chapter focused on identification of a major factor enhancing DPAA transformation under ariaerobic conditions. As a result, the elimination of DPAA in Gleysol soils (Qiqihar and Shindori soils) was more rapid than in Mollisol and Regosol soils (Heihe and Ikarashi soils, respectively) during a 5-week incubation. No clear relationship between decreasing rates of DPAA concentrations and soil Eh values was found. The Ikarashi soil showed the slowest decrease in DPAA concentrations among the four soils, but the transformation of DPAA was notably enhanced by addition of exogenous sulfate together with acetate, cellulose or rice straw. Addition of molybdate, a specific inhibitor of sulfate reduction, resulted in the stagnation of DPAA transfbnnation, suggesting that indigenous sulfate reducers play a role in DPAA transformation under anaerobic conditions. As metabolites of DPAA, arsenate, phenylarsonic acid, phenylmethylarsinic acid, diphenylmethylarsine oxide and three unknown arsenical compounds were detected by LC-ICPMS analysis. Subsequently, LC-TOEMS analysis revealed that the major unknown could be assigned to diphenylthioarsinic acid (DPTAA). This is the first study to reveal enhancement of DPAA transformation under sulfate-reducing conditions. In Chapter IV, the isolations of anaerobic microorganisms capable of transforrning DPAA under sulfate-reducing conditions were examined using a limiting dilution culture method and an anaerobic plate culture method. As a result, four positive microbial consortia that could transform DPAA to DPTAA were obtained. Then, bacterial 16S rRNAgene libraries were constructed and the sequences were determined. The sequencing results revealed that all the positive consortia contained Desulfotomaculum acetoxidans species. In contrast, absence of dsrAB, dissimilatory sulfite reductase genes, was confirmed in the negative consortia showing no DPAA reduction. These findings strongly suggest that sulfate-reducing bacteria including D. acetoxidans take a role in the anaerobic transformation of DPAA to DPTAA. In conclusion, this study elucidated that, l) the presence of DPAA did not distinctly change soil bacterial and archaeal communities under submerged and anaerobic conditions, 2) the microbial transformation of DPAA in soil could be enhanced under sulfate-reducing conditions, and 3) sulfate-reducing bacteria such as D. acetoxidans could participate in transforming DPAA to DPTAA under sulfate-reducing conditions. Based on 2) and 3), generation of DPTAA under sulfate-reducing conditions is attributed to reaction between DPAA and hydrogen sulfide released by sulfate-reducing bacteria. To the best of our knowledge, the role of sulfate reduction in transformation of phenylarsenicals in anaerobic conditions has not been previously reported. The findings in this study can provide a novelinsight for biotransformation of phenylarsenicals in contaminated soils., 学位の種類: 博士（農学）. 報告番号: 甲第3790号. 学位記番号: 新大院博（農）甲第121号. 学位授与年月日: 平成25年3月25日, 新大院博（農）甲第121号},
 title = {Microbial effects and biotransformation of diphenylarsinic acid in anaerobic soils},
 year = {2013}
}