Although arsenic is ubiquitous in the environment, certain forms of arsenic are added deliberately in ever increasing quantities. The addition of large quantities of the trivalent inorganic form (arsenite) could pose a serious hazard because of the toxicity of this form explicable in terms of its action of sulfhydryl containing enzymes and/or coenzymes. In the environment B.rsenite is rapidly converted to arsenate (the pentavalent inorganic form). Since a biological explanation for the oxidation of arsenite to arsenate was available only for cattle dips (a unique environment), this study was undertaken to examine sewage for the presence of arsenite oxidizing bacteria. The isolation of bacteria capable of arsenite oxidation would allow a study of cultural and physiological properties and thus provide information useful in making rational decisions regarding the continued use of inorganic arsenicals as pesticides; as well as elucidating one segment of the arsenic cycle. Thirty-four different strains of arsenite oxidizing pseudomonads were isolated from sewage and classified into two major groups, Pseudomonas fluorescens-arsenoxydans and Pseudomonas acidovorans-arsenoxydans, with three and four ecotypes in each group. One particularily rapid arsenite oxidizing strain (designated Pseudomonas acidovorans-arsenoxydans YE56) was extensively studied. A minimal, defined medium was used to study the relationship of temperature, pH, aeration and nutrition to growth of this organism versus the ability of the organism to convert arsenite to arsenate under the same conditions. The conversion of arsenite to arsenate in YE56 was shown to be due to the appearance at stationary phase of an enzyme and/or component of the electron transport system when the organism is grown in chemically defined medium. In contrast, induction of the arsenite oxidizing system occurs in late exponential growth phase when the organism is grown in a rich medium. Thus, even though cell populations may never reach stationary phase in sewage, the ability of organisms to oxidize arsenite is probably constant. No energy could be detected from the oxidation of arsenite as measured by increase in growth rate or total cell yield. The adaptability of this organism to the changing environmental conditions of a sewage plant helps explain the findings that pseudomonads are the predominant species in sewage. A simple, unambiguous method for the separation of arsenite, arsenate and phosphate, using a combination of thin layer chromatography and paper chromatography, is described which makes it possible for investigators to define arsenic determinations to include the form (organic or inorganic), oxidation state (trivalent or pentavalent) and the quantity present in the samples.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-1821 |
| Date | 01 January 1974 |
| Creators | Phillips, Shirley E. |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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