|Taurine as a nitrogen source for bacteria
Taurine, originally explored as a source of carbon, was also found to be a source of nitrogen, but the phenomenon was not examined in detail.
Taurine can serve as a sole source of nitrogen for Rhodococcus opacus (in the presence of additional carbon), just as it can serve as a sole source of carbon. The same degradative pathway (taurine transaminase and Xsc) is used by the organism under the two conditions, though the level of expression is lower when the nitrogen limitation is involved. Corresponding to the presence of the complete dissimilatory pathway, the sulfonate-sulfur is recovered as sulfate. This release of sulfate, when taurine is a sole source of nitrogen, turns out to be a rarity. Most organisms (90 %) isolated to utilize taurine/nitrogen do not share this trait.
The first example of the excretion of something other than sulfate was found in Rhodopseudomonas palustris. In this case, sulfoacetate was the product, which was recovered quantitatively in the growth medium.
Thus sulfoacetate, which had previously been considered to be a product from sulfoquinovose, was shown to be a novel product from taurine. The explanation for this excretion is surely homeostatic, to maintain a constant ionic strength in the cell. It follows that there is a specific exporter, which has not yet been identified. The gene encoding the specific, NAD-coupled sulfoacetaldehyde dehydrogenase [EC 1.2.1.-] has also not been identified.
It was presumed, that the release of sulfoacetate from taurine under these conditions would be widespread, but is was not found under the conditions we used. Instead we discovered the release of sulfoacetaldehyde or isethionate.
There must be specific efflux systems for these sulfonates.
The generation of sulfoacetaldehyde in R. palustris involves a taurine dehydrogenase, which requires a native cytochrome c. The generation of sulfoacetaldehyde in Acinetobacter calcoaceticus also involves taurine dehydrogenase. In contrast, taurine aminotransferase generates sulfoacetaldehyde in Klebsiella oxytoca, which involves a soluble, NADP-coupled isethionate dehydrogenase.
- Styp von Rekowski, K., K. Denger, and A. M. Cook. 2005. Isethionate as a product from taurine during nitrogen-limited growth of Klebsiella oxytoca TAU-N1. Arch. Microbiol. 183:325-330.
- Weinitschke, S., K. Styp von Rekowski, K. Denger, and A. M. Cook. 2005. Sulfoacetaldehyde is excreted quantitatively by Acinetobacter calcoaceticus SW1 during growth with taurine as sole source of nitrogen. Microbiology (Reading UK) 151:1285-1290.
- Denger, K., S. Weinitschke, K. Hollemeyer, and A. M. Cook. 2004. Sulfoacetate generated by Rhodopseudomonas palustris from taurine. Arch. Microbiol. 182:254-258.
- Denger, K., J. Ruff, D. Schleheck, and A. M. Cook. 2004. Rhodococcus opacus expresses the xsc gene to utilize taurine as a carbon source or as a nitrogen source but not as a sulfur source. Microbiology (Reading UK) 150:1859-1867.