Mechanisms of Competition and Coexistence in Freshwater Algae and Bacteria

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9418096 Grover Different species of organisms compete for the resources needed for growth. Theoretically, such competition can lead to extinction of all species but the best competitor. Algae and bacteria in freshwater habitats often compete for dissolved phosphorus, an essential nutrient, but are observed to coexist in most habitats, despite the superior competitive ability of bacteria. The mechanisms that allow this coexistence are currently unknown, and this study will use laboratory investigations to explore them. This will be done by growing algae and bacteria together under defined conditions, identifying the organisms that coexist, and determining their properties that allow coexistence. Working hypotheses to be examined in these studies include (1) the possibility that lack of a sufficient supply of dissolved organic carbon, required by bacteria but not algae, limits the ability of bacteria to consume phosphorus, (2) the possibility that algae and bacteria specialize on chemically distinct forms of phosphorus, (3) the possibility that when phosphorus supply varies, algae are best able to store phosphorus acquired at elevated concentrations, while bacteria are best able to acquire phosphorus at low background concentrations, and (4) the possibility that protozoa eating bacteria, but not algae, limit the growth of bacteria, thus allowing algae to acquire phosphorus. Excessive algal growth is a common water quality problem, and such excessive growth is often related to the phosphorus supply that a body of water receives. Understanding the competitive balance between algae and bacteria in acquiring this phosphorus will help provide a scientific basis for management of water quality.