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Title: Evidence for polyphosphate accumulating organism (PAO)-mediated phosphorus cycling in stream biofilms under alternating aerobic/anaerobic conditions

Author
item SAIA, SHEILA - Cornell University
item SULLIVAN, PATRICK - Cornell University
item REGAN, JOHN - Pennsylvania State University
item CARRICK, HUNTER - Central Michigan University
item Buda, Anthony
item LOCKE, NICOLAS - Pennsylvania State University
item WALTER, TODD - Cornell University

Submitted to: Freshwater Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2016
Publication Date: 2/24/2017
Citation: Saia, S.M., Sullivan, P.J., Regan, J.M., Carrick, H.J., Buda, A.R., Locke, N.A., Walter, T. 2017. Evidence for polyphosphate accumulating organism (PAO)-mediated phosphorus cycling in stream biofilms under alternating aerobic/anaerobic conditions. Freshwater Science. 46(2):284-296. doi: 10.1086/691439.

Interpretive Summary: Understanding how aquatic organisms influence nutrient cycling in streams is critical to advancing our knowledge of nutrient fate and transport. In this experiment, we collected bottom-dwelling groups of bacteria, algae, and diatoms (biofilms) from rocks in a small mixed land-use stream, subjected them to alternating levels of light and dissolved oxygen in the laboratory, and assessed the effects of these daily patterns on phosphate concentrations in stream water and in the biofilms themselves. In the daytime, the presence of light and high dissolved oxygen levels led to phosphate uptake by stream biofilms and low phosphate concentrations in stream water. The exact opposite pattern occurred at night. Findings reveal the importance of stream biology on daily nutrient uptake and release patterns in streams.

Technical Abstract: Phosphorus (P) is often a limiting nutrient in freshwater ecosystems and excessive inputs can lead to eutrophication. In-stream cycling of P involves complex biological, chemical, and physical processes that are not fully understood. Microbial metabolisms are suspected to control oxygen-dependent uptake and release of P in stream sediments and biofilms but specific organisms have not been identified. Polyphosphate accumulating organisms (PAOs) are largely studied under controlled conditions in the context of phosphorus removal from wastewater. However, little work has been done to evaluate the role PAOs may play in biogeochemical P cycles. We hypothesized diel light cycles trigger alternating aerobic/anaerobic conditions in the streams that promote patterns of P uptake/release similar to those attributed to PAOs in wastewater treatment. To test this hypothesis, intact, stream biofilms were collected and subjected to laboratory treatments: (1) continuous sparging with air and (2) alternate sparging between air and an anaerobic gas. The concentration of phosphate and other analytes in the surrounding water were monitored throughout the experiment, while the total phosphorus (TP) and polyphosphate (polyP) concentration in the biofilms were measured at the start and end of the experiment. Microscopy was used to quantify the percent of cells with stored intracellular polyP and polymerase chain reaction (PCR) was used to test for the presence of known PAO genes. Similar to patterns during wastewater treatment, surrounding water had significantly larger phosphate concentrations in samples taken during anaerobic conditions compared to aerobic conditions. Microscopy revealed significantly higher percentages of stored intracellular polyP during aerobic conditions compared to anaerobic conditions. Previously reported PAO genes were not found in our stream biofilms. Thus, PAO-mediated P cycling in ecosystems under alternating aerobic-anaerobic conditions may be common and deserves further study.