Characterization of Reduced Phosphorus Metabolism in Alcaligenes Faecalis WM2072 and Xanthobacter Flavus WM2814

155 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.The studies presented herein describe the characterization of reduced phosphorus metabolism in two recently isolated bacteria. These bacteria were found by performing enrichments to isolate organisms that could utilize reduced phosphorus compounds as their sole phosphorus source. Two of these isolates that grew well using either hypophosphite or phosphite were identified by 16s rDNA analysis as a strain of Alcaligenes faecalis and a strain of Xanthobacter flavus. The genes required for oxidation of hypophosphite and phosphite by these organisms were identified using transposon mutagenesis and directed mutagenesis experiments. For A. faecalis these include homologs of the ptxD and htxA genes from Pseudomonas stutzeri WM88, which encode an NAD:phosphite oxidoreductase (PtxD) and 2-oxoglutarate-dependent hypophosphite dioxygenase (HtxA). HtxA and PtxD were shown to be required for the utilization of phosphite and hypophosphite by A. faecalis. This organism also has the htxBCD genes that comprise an ABC type transporter, presumably for hypophosphite and phosphite transport. X. flavus also has homologs of the ptxD and htxBCD genes from Pseudomonas stutzeri WM88. However, X. flavus has a novel pathway for the oxidation of hypophosphite to phosphite: a putative hypophosphite dehydrogenase encoded by the htxXY genes that is homologous to soluble NAD-dependent formate dehydrogenases. Additional transposon-induced mutants suggest that the ability of X. flavus to use hypophosphite as a phosphorus source also requires the synthesis of a molybdopterin cofactor as well as a gene, designated htxZ, that encodes a homolog of an accessory protein for soluble NAD-dependent formate dehydrogenases. Experiments in the heterologous host Xanthobacter autotrophicus show that htxX and htxY are required for hypophosphite oxidation and ptxD is required for phosphite oxidation in this organism.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD