Control of heme content in Vitreoscilla by oxygen.

Abstract

Protoheme IX is the only heme type present in Vitreoscilla, an obligate aerobe of the Beggiatoaceae family. Previous work showed that the heme content of Vitreoscilla cells was very dependent on growth conditions and that cells with high heme content also had a higher respiratory rate and a higher concentration of cytochrome o, the terminal oxidase. Experiments reported here showed that oxygen exerts a primary control on the heme content of Vitreoscilla and that the concentration of the peptone-yeast extract-acetate medium (PYA) was also important. There was an optimum shaking rate at each PYA concentration for maximum heme content and an optimum PYA concentration for each shaking rate. The atmospheric oxygen concentration of the shaking growth medium remained at 100% saturation and then began a rapid decline (t1/2 ca. 1hr) to less than 10% saturation. The time at which this decline began depended on both the PYA concentration and shaking rate at a fixed inoculum. The heme content of the cells increased over 50 fold as the oxygen concentration in the medium decreased during culture. Cells with a sub-maximal heme content exposed for two hr to 1) anaerobic conditions showed a 15% decrease in heme content; 2) 50% atmospheric oxygen, a 26% increase in heme content; 3) 100% atmospheric oxygen, an 80% decrease in heme content. The results show that the optimal oxygen concentration for maximum heme content in Vitreoscilla is relatively low, probably less than 10% atmospheric.