Effects of the metalloid oxyanion tellurite (TeO32-) on growth characteristics of the phototrophic bacterium Rhodobacter capsulatus

This work examines the effects of potassium tellurite (K2TeO3) on the cell viability of the facultative phototroph Rhodobacter capsulatus. There was a growth mode-dependent response in which cultures anaerobically grown in the light tolerate the presence of up to 250 to 300 mug of tellurite (TeO32-) per ml, while dark-grown aerobic cells were inhibited at tellurite levels as low as 2 mug/ml. The tellurite sensitivity of aerobic cultures was evident only for growth on minimal salt medium, whereas it was not seen during growth on complex medium. Notably, through the use of flow cytometry, we show that the cell membrane integrity was strongly affected by tellurite during the early growth phase (less than or equal to50% viable cells); however, at the end of the growth period and in parallel with massive tellurite intracellular accumulation as elemental Te-0 crystallites, recovery of cytoplasmic membrane integrity was apparent ( greater than or equal to90% viable cells), which was supported by the development of a significant membrane potential (DeltaPsi = 120 mV). These data are taken as evidence that in anaerobic aquatic habitats, the facultative phototroph R. capsulatus might act as a natural scavenger of the highly soluble and toxic oxyanion tellurite.