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Changes in pH of an Anaeroboic Bacterial Culture Grown in a 3 L Bioreactor and Amended with Oxyanions of Selenium

L. Eriksen, Jr. and T.G. Chasteen
Department of Chemistry
Sam Houston State University
Huntsville, Texas, 77340 USA


Cultures of Pseudomonas fluorescens strain K27 were grown into stationary phase in anaerobic cultures on a complex medium with 3% nitrate. Cell population, measured by optical density, and pH were determined hourly in time course experiments that extended over 8 to 10 hours. Cultures were amended with either selenate, selenite or mixtures of these oxyanions. Selenite appears to be more toxic than selenate as measured by specific growth rate. Selenium-free controls of this faculatative anaerobe dropped from an initial pH of 7.4 to 7.2 while growing into stationary phase. Ten mM selenite-amended cultures increased in pH to about 8; while 10 mM selenate-amended cultures remained basically at the pH of the initially inoculated medium. No significant trend in pH was apparent among the five different amendements regimes run in triplicate; however the largest variability among replicates was for non-equimolar mixtures of selenate and selenite.

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