Control of heme content in Vitreoscilla by oxygen.

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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 O2 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 skaking rate. The atmospheric O2 concentration of the skaking growth medium remained at 100% saturation and then began a rapid decline (t1/2 about 1 h) to < 10% saturation. The time at which this decline began depended on both the PYA concentration and skaking rate at a fixed inoculum. The heme content of the cells increased over 50-fold as the O2 concentration in the medium decreased during culture. Cells with a sub-maximal heme content exposed for 2 h to 1 anaerobic conditions showed a 15% decrease in heme content; 50% atmospheric O2, a 26% increase in heme content; 100% atmospheric O2, an 80% decrease in heme content. The optimal O2 concentration for maximum heme content in Vitreoscilla is relativley low, probably < 10% atmospheric.