Fisheries Research Report No. 1710, 1966

Michigan Department of Conservation
Research and Development Report No. 50
Institute for Fisheries Research Report No. 1710, 1966
Bacterial Transport of Phosphorous in a Stream Ecosystem

Frank F. Hooper
Institute for Fisheries Research
Ann Arbor, Michigan, U. S. A.

and

Robert C. Ball
Department of Fisheries and Wildlife
Michigan State University
East Lansing, Michigan, U. S. A.

      Abstract.-Tracer quantities of radioactive phosphorous (³²P) added to a trout stream equilibrate rapidly with water-borne solids and are assimilated into the food chain. Previous studies [1] have suggested that the rate of entry into the food chain and the pathways taken by phosphorous may be strongly influenced by the amount and kind of suspended solids (e.g. bacteria and algae) present in the water at the time phosphorous is added to the stream. The present experiment, in which bacteria labeled with ³²P were added to a stream, was designed to test the efficacy of bacteria as agents of phosphorous transport and to better define their position in the phosphorous cycle of freshwater streams.

      Much of the information on the role of bacteria in the cycling of phosphorous comes from laboratory and quasi field experiments. Hayes and Phillips [2] followed the exchange of ³²P through 100 or more artificial systems consisting of lake water, mud and in some instances aquatic macrophytes and phytoplankton. The action of bacteria was demonstrated by comparing the flow of ³²P in systems with and without antibiotics. These experiments demonstrated that the bacteria (1) equilibrate rapidly with the added phosphorous, (2) maintain phosphorous in the water phase and delay its incorporation into mud and rooted plants, and (3) convert inorganic phosphorous into soluble organic phosphorous compounds at a relatively rapid rate. Hayes [3] noted a much greater uptake of ³²P by Gammarus in normal than in sterilized sea water, suggesting that bacteria may greatly enhance flow of ³²P to higher levels of the food chain. Working with sea water systems Pomeroy [4] was able to verify the inhibition of phosphorous release from solids by antibiotics and found that methylene blue and cyanide blocked phosphorous uptake. These findings indicated that metabolic processes were involved. Rigler [5] noted the rapid turnover of phosphorous in the surface waters of lakes treated with ³²P. From laboratory experiments and from experiments with polyethylene bags suspended in the lake, he concluded that bacteria were responsible for the rapid turnover of phosphorous and suggested that they might compete with algae for inorganic phosphorous.

      The above studies have shown a close association between phosphorous concentration and bacterial activity but they have not identified the chemical state of the phosphorous and its location in or on the bacterial cell. It is clear that phosphorous is absorbed on cell surfaces and this source would be far more labile than phosphorous within the cell with regard to its use in natural systems. Phosphorous within the bacterial cell exists chiefly as nucleotides. For cultured Escherichia coli Taylor [6] found 2.72% of the dry weight of E. coli cultured in broth was phosphorous of which 85% was in the form of nucleic acid and 12% phospholipids. Phosphorous incorporated into E. coli by culturing this species in nutrient broth has been show to be fixed within the cell and is not subject to exchange with the medium [7]. Phosphorus in this form may remain relatively unavailable to photosynthetic organisms until the cell dies and decays. Consumers, e.g. filter feeders, could, however, incorporate this type of phosphorous into the food chain. Specifically in this experiment we planned to investigate the translocation of phosphorous within the food chain of a stream when (1) phosphorous was bound intracellularly into a bacteria cell (E. coli) and thus (2) was available to producers only after mineralization, and (3) when the largest input of phosphorous to the higher levels of the food chain would be to filter feeders and to detritus feeders capable of utilizing E. coli after the cells are deposited on the stream bottom.

      The authors wish to acknowledge contributions made to this study by Michael Bender, James Bacon, Tom Wojtalik and Naylord Urshel. Dr. Carl Latta and the staff of the Pigeon River Trout Research Station assisted in many ways.