Abstract:
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.
