Selenium uptake byButyrivibrio fibrisolvensandBacteroides ruminicola

Abstract

The uptake and incorporation of 75[Se]selenite by Butyrivibrio fibrisolvens and Bacteroides ruminicola were by constitutive systems. Rates of uptake were higher in chemostat culture than in batch culture and there may be some inducible component. Uptake of [75Se]selenite was distinct from sulphate or selenate transport, since sulphate and selenate did not inhibit selenite uptake, nor could sulphate or selenate uptake be demonstrated in these organisms. Selenite uptake in B. fibrisolvens had and apparent Km of 1.74 mM and a Vmax of 109 ng Se · min−1 · (mg protein)−1. An apparent Km of 1.76 mM and Vmax of 1.5 μg Se · min−1 · (mg protein)−1 was obtained for B. ruminicola. [75Se]Selenite uptake by both organisms was partially sensitive to inhibition by 2,4-DNP. Uptake by B. fibrisolvens was also partially inhibited by azide and arsenate and in B. ruminicola it was partially inhibited by fluoride. CCCP, CPZ, DCCD or quinine did not inhibit uptake in either B. fibrisolvens or B. ruminicola. Selenite transport by both organisms was sensitive to IAA and NEM and was strongly inhibited by sulphite and nitrite. [75Se]Selenite was converted to selenocystine, selenohomocystine and selenomethionine by B. fibrisolvens. B. ruminicola did not incorporate [75Se]selenite into organic compounds, but did reduce it to red elemental selenium.