The Research Of Roxarsone Transformation By Shewanella Oneidensis MR-1

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been extensively used as food additive in animals feeding, which is usually excreted unchanged in manure and eventually enters in soil and water, resulting in potential arsenic pollution. Shewanella is a kind of facultative anaerobe existing widely in soil, ocean and other water environment, which is able to utilize diverse electron acceptors, such as Fe3+, NO3-, NO2-, heavy metal ions and so on, in metabolism under anaerobic conditions. In this study, Shewanella oneidensis MR-1 is selected as mode strain bacteria used in roxarsone biotransformation. The main conclusions are listed as follows:The feasibility of biological transformation of roxarsone by S. oneidensis MR-1 in aqueous anaerobic system:S. oneidensis MR-1 could make roxarsone as the final electron acceptor, and reduced it to 3-amino-4-hydroxy phenylarsonic acid(HAPA) in the anaerobic aqueous environment, which was the only reductant product detected. However, roxarsone could not be transformed directly by S. oneidensis MR-1 in the absence of exogenous substrates, proving that roxarsone can not be use as the available carbon source for biotransformation in short term. The results of different intial roxarsone concentrations experiments indicated that roxarsone did not inhibite the growth of S. oneidensis MR-1.The effects of dissolved Fe(Ⅲ) on roxarsone biotransformation by S. oneidensis MR-1 under aqueous anaerobic environment:in the existence of S. oneidensis MR-1, the presence of soluble Fe(Ⅲ) could obviously promote the transformation of roxarsone. At the same time, the secondary iron ores was found in the system, which may cause the adsorption of HAPA, reducing the mobility of arsenic. High concentrations of soluble Fe(Ⅲ) can not promote the biotransformation of roxarsone by S. oneidensis MR-1. Low level of soluble Fe(Ⅲ) (2.0 mmol/L) can promote the biotransformation of roxarsone. Because of the different secondary iron ores formed at different concentrations of soluble Fe(Ⅲ), the different quantity of 3-amino-4-hydroxy phenylarsonic acid (HAPA) is adsorbed.In the porous media circumstance with different water content, S. oneidensis MR-1 secreted extracellular polymers (EPS) increased with the decreasing water content. The fluctuations of water content obvious affected the roxarsone transformation by S. oneidensis MR-1. As water content was higher enough, to provide water environment for S. oneidensis MR-1 growth, reproduction and electron transfer, roxarsone can be transformed with S. oneidensis MR-1. The higher water content, the higher transformaton efficiency of roxarsone.