Analysis of Environmental Bacteria Capable of Utilizing Reduced Phosphorus Compounds

ABSTRACT ANALYSIS OF ENVIRONMENTAL BACTERIA CAPABLE OF UTILIZING REDUCED PHOSPHORUS COMPOUNDS by Brandee L. Stone Master of Science in Biological Sciences California State University, Chico Summer 2011 Although bacterial metabolic pathways to oxidize the reduced phosphorus compounds hypophosphite and phosphite have been characterized, bacterial reduced phosphorus oxidation in the environment and the impact of this activity on P biogeochemistry has largely been overlooked. In this study, I attempted to answer two of the basic questions in this field: (1) how abundant are culturable reduced phosphorus oxidizing bacteria in a variety of soils and sediments; and (2) how common are previously characterized bacterial pathways to oxidize hypophosphite and phosphite. To determine how common the ability is in the environment to oxidize hypophosphite and phosphite, I used a 5-tube most probable number method to estimate the concentrations of viable hypophosphite and phosphite oxidizing bacteria from 12 natural aquatic and terrestrial environments in northern California. The percent of total culturable bacterial concentrations able to use these reduced phosphorus compounds as a sole source of phosphorus were: hypophosphite, 7-100%; phosphite, 10-67%; and aminoethylphosphonate, 34-270%. Relatively high concentrations of reduced phosphorus oxidizing bacteria were found in both pristine sites and sites with urban and agricultural disturbance, and did not correlate with likely concentrations of reduced phosphorus compounds. Concentrations of reduced phosphorus oxidizing bacteria in anoxic sediments were similar to those in soils. I isolated 19 bacteria able to grow on reduced phosphorus sources, including Proteobacteria (Pseudomonas, Acinetobacter, Variovorax, and Bradyrhizobium), and two actinobacteria, suggesting a far wider phylogenetic occurrence of reduced phosphorus oxidation than previously known. To detect pathways responsible for reduced phosphorus oxidation, I characterized one gene responsible for hypophosphite oxidation, htxA, and one gene for phosphite oxidation, ptxD, in these isolates. These genes have previously only been described for a few closely related taxa. I found all isolates possessed a ptxD ortholog, though not all were capable of growth on phosphite. Partial sequence analysis showed ptxD was 100% identical to one previously characterized. Thirteen isolates possessed htxA, though two were not capable of growth on hypophosphite. My results indicate reduced phosphorus oxidizing bacteria and the genes required for the oxidation of hypophosphite and phosphite are abundant in the environment, and provide strong evidence for the importance of bacterial phosphorus oxidation in nature.