Competition And Uptake Between Heterotrophic Bacteria And Algae For Phosphate

The interactions between marine heterotrophic bacteria and phytoplankton involve a wide range of interacting ecological relationships, including commensalisms and competition. Commensalisms occurs in the production of dissolved organic carbon (DOC) by phytoplankton and its utilization by heterotrophic bacteria. The production of DOC is dependent on the availability of inorganic nutrients, for which phytoplankton and bacteria compete. In this paper, marine heterotrophic bacteria and algae are incubated in bacteria pure culture (B.P.C.), algae pure culture ( A.P.C.)and mixed culture(M.C.), on different organic carbon and inorganic phosphate concentration. The interactions of heterotrophic bacteria and algae to the nutrient elements are discussed,while the competitions between algae and bacteria to inorganic phosphate are explored.The main results and conclusions are listed as follows:1. Under the concentrations of the experiment, the growth rates of heterotrophic bacteria are higher than algae; in the presence of an external carbon source, bacterial growth rates increase significantly. The exponential growth of bacteria will extend when organic carbons are added and nutrients in the culture are abundant.2. In the mixed culture, bacterial and algal growth and P-takeups are less than pure culture.3. Inorganic phosphate can be stored during the growth of algal .This mechanism would enhance their ability to compete for the nutrition with bacteria; additions of external carbon have beneficial to bacterial P-takeup.4. Competition and uptake between marine heterotrophic bacteria and algae for phosphate are related to the phosphate concentrations of culture medium. In this paper, the critical phosphate concentration is 1μmol P / L, at low concentrations (<1μmol P / L),external carbon source have a significant effect on algal P-takeup;at high concentration (> 1μmol P / L), algal P-takeup is hardly affected by organic carbon additions. The critical concentration may be biased due to different types of algae.