A five-gene cluster involved in utilization of taurine-nitrogen and excretion of sulfoacetaldehyde by Acinetobacter radioresistens SH164

Acinetobacter calcoaceticus SW1, under nitrogen limitation, assimilates the nitrogen moiety of taurine (2-aminoethanesulfonate) inducibly and excretes sulfoacetaldehyde, a product of taurine dehydrogenase (TauXY). BLAST searches of newly available genome sequences using the TauXY sequences revealed a 5-gene cluster, tauRXYPI, in Acinetobacter radioresistens SH164. We hypothesized that tauXYPI (HMPREF0018_00717-HMPREF0018_00720) encodes proteins that are orthologs of the undefined pathway from strain SW1, and that tauR (HMPREF0018_00716) encodes the relevant transcriptional regulator. Strain SH164 excreted sulfoacetaldehyde from taurine during growth. TauXY activity was expressed inducibly. Reverse transcription PCR showed that the tauRXYPI genes were transcribed inducibly. This allowed the conclusions that (i) TauP (currently annotated as permease GabP [TC 2.A.3]) is a taurine permease, and (ii) TauI (currently annotated as DUF6 drug/metabolite exporter [TC 2.A.7]) is a sulfoacetaldehyde exporter. The presumably equifunctional cluster tauRXYPI was then found in strain SW1. TauP is the third recognized taurine uptake system, and TauI is the third postulated class of sulfonate exporters, in bacteria.