Study of selenite resistance in stenotrophomonas maltophilia Oak Ridge strain 02 and pseudomonas sp. PC37

Abstract

Stenotrophomonas maltophilia Oak Ridge strain 02 (S. maltophilia 02) and Pseudomonas sp. PC37 (PC37) were isolated from a heavy metal contaminated site in Oak Ridge, TN, and demonstrated the ability to grow in the presence of toxic levels of different metals. This study focused on the tolerance or resistance of bacteria to selenite, an oxyanion of selenium. When grown in the presence of 0.5 mM selenite, S. maltophilia 02 produced a red precipitate, which is most likely, elemental selenium. However, PC37 did not produce the red precipitate when grown in 0.5 mM selenite. From these observations, we hypothesized that S. maltophilia 02 used a selenite reduction mechanism for resistance to 0.5 mM selenite, whereas PC37 used a selenite exclusion mechanism. The growth of both strains was measured in the presence of 0.5 mM selenite by turbidity measurement and by counting viable cells. Selenium in the cells and in the growth medium was measured by inductively coupled plasma (ICP) atomic emission spectroscopy. During the 10 hour growth period of S. maltophilia 02, the concentration of selenite in the growth medium decreased from 0.5 mM to 0.3 mM, while the selenium content in the cells increased from 0 to 0.1 mM. As expected, ICP quantitative analysis of the selenium concentration in PC37 did not show any significant change in the concentration of selenite in the growth medium or in the cell mass.