Biotransformation of adenine and cytokinins by the rhizobacterium Serratia proteamaculans.

Approximately 60,000 microorganisms from Saskatchewan soil were screened for growth on the cytokinin N6-benzyladenine (BA) as C source. A single isolate, identified as Serratia proteamaculans, grew well on BA. The culture filtrates from S. proteamaculans were screened using reversed phase high performance liquid chromatography (RP-HPLC) for the presence of secondary metabolites. The analysis revealed a major metabolite and its chemical structure was deduced as 8-hydroxy-N6-benzyladenine (8-OHBA). Subsequently, the S. proteamaculans isolate was also found to metabolize N6-(2-isopentenyl)adenine and adenine through oxidation of C-8 of the purine ring. A clone of the S. proteamaculans xanthine dehydrogenase (Xdh, EC 1.1.1.204) encoding genes was isolated in Escherichia coli. This E. coli isolate metabolized BA to 8-OHBA. Similar to other bacterial Xdh, the S. proteamaculans enzyme was composed of two subunits. The derived amino acid sequences of these Xdh subunits were most similar (XdhA, 60%; XdhB, 72%) to those of Pseudomonas aeruginosa.