Distribution of Phytate Mineralizing Bacteria Along a Small Creek in the Chesapeake Bay Watershed.

Phosphorus (P) can contribute to eutrophication if present at high concentrations. In the Chesapeake Bay watershed, soils having some of the highest P concentrations in the region have been identified. Microorganisms are major drivers for formation and transformation of organic P and mobilization/immobilization of inorganic P through mechanisms such as the production of enzymes or acidification by released organic molecules. In order to understand the contribution of microorganisms to P release, we analyzed sediment and water collected along a tributary to the Chesapeake Bay that originates in agricultural fields. We isolated and screened bacteria from five sites ranging from agricultural headwaters to wetlands at the mouth of the creek.  Bacteria isolated from these sites were identified as those commonly found in water, wastewater, animal waste, or plant rhizospheres, including Pantoea, Pseudomonas, Serratia, Salmonella, and Enterobacter.  These bacteria were further characterized as phosphate solubilizing bacteria (PSB) and phytate mineralizing bacteria (PMB). These bacteria showed distinct differences in ability to utilize P between sites near the headwaters and the mouth of the creek. For example, almost all of the bacteria (95%) isolated from surface waters at the headwaters were able to mineralize phytate, whereas only about a third of isolates from the mouth could.  For inorganic P, 65% of isolates from water at the headwaters were able to solubilize P, and this number decreased by about half for waters at the mouth. In general, sediment isolates were less capable of solubilizing P and mineralizing phytate than water isolates, although phytate concentrations in sediments were higher than those in water, indicating that phytate may be sequestered in sediments and unavailable for microbial mineralization.  Our findings suggest that microbial activity may play an important role in P release, and will be helpful for effective nutrient management to reduce P load in the Chesapeake Bay.