Predatory Behaviors in Bacteria—Diversity and Transitions

N utrient and energy flows among organisms can be depicted as webs within which predatory interactions are extremely important. Predatory behaviors often dominate top-to-bottom relationships, while productivity tends to control bottom-to-top flows. Prokaryotes in the environment are usually depicted as bottom-of-the-web members, responsible for two main activities: primary production of nutrients and nutrient recycling through their degradative and saprophytic capacities. However, prokaryotes have colonized this planet for about 3.8 billion years, and might have been its only inhabitants for 1 to 1.5 billion years before the appearance of unicellular grazing eukaryotes, providing ample time for predatory behaviors to emerge. Because predatory interactions between prokaryotes are difficult to study, however, our understanding of their evolution and of their role in nature is limited. Predatory bacteria are found in virtually every habitat, including in rivers, groundwater, estuaries, the open ocean, sewage, soils, plant roots, and animal feces. In addition, environmental 16S rRNA gene sequences deposited in databases reveal that predatory bacteria also live in contaminated soils and extreme environments. These micropredators make up a diverse assemblage.