Wen-Ing Hwang

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)




For several decades, excessive levels of selenium in feeds have been known to cause various toxic symptoms in livestock. Excessive selenium levels in feeds are the result of plants growing on soils which contain significant levels of selenium. The natural cycling process by which selenium becomes available appears to involve various chemical weathering processes. In addition, microbial action may play a direct or indirect role in rendering selenium soluble. (1). The extent to which microoganisms are involved in the natural cycling processes has been subject to considerable discussion. It has been demonstrated that mold can convert selenate or selenite to a volatile substance with a garlic-like odor. The substance has been identified as dimethyl selenide (2). Other workers (3,4) showed that the addition of selenite or selenite to soils resulted in the volatilization or loss of selenium. The volatilization was shown to be due to microbiological action, but the identity of the organisms was not determined. Unpublished work from South Dakota State University has indicated that bacteria might also be involved in the methylation of selenium. Recently, other workers (5) have isolated one coryneform bacterium which can convert inorganic selenium to dimethyl selenide. This is not necessarily surprising since bacteria have been shown to be involved in the methylation of mercury and arsenic (6,7). Since little is known concerning the actual involvement of bacteria in the natural cycling of selenium, this study was undertaken for the following purposes: 1. To isolate and identify soil bacteria which are capable of converting inorganic selenium to volatile compounds. 2. To identify the volatile selenium compounds generated by the isolated bacteria.

Library of Congress Subject Headings


Selenium -- Physiological effect


Soils -- Selenium content



Number of Pages



South Dakota State University