Phagotrophy

Phagotrophy is a feeding strategy in which an organism ingests solid food by phagocytosis. Particulate food can include bacteria, microalgae, detrital particles, and other microorganisms. Phagotrophy is common in many unicellular protists and in the phagocytic cells of animals, such as macrophages and neutrophils; it is less common in plants and most algae, which rely on osmotrophy or photosynthesis, though some protists are mixotrophic and can combine phagocytosis with other nutritional modes.

Mechanism: In phagocytosis, surface receptors recognize targets, and the cytoskeleton (actin) reorganizes to extend membrane around the particle, forming a phagosome. The phagosome fuses with lysosomes, creating a phagolysosome where digestive enzymes break down the contents. Resulting nutrients are absorbed by the cell; indigestible material is expelled by exocytosis. Phagocytosis is energy-dependent and size-limited by the organism's capacity to engulf particles.

Ecological role: Phagotrophy is a major pathway for transfer of energy from bacteria and algae to higher trophic levels and is an important component of microbial food webs. In aquatic systems, protozoan phagotrophy regulates microbial populations and influences carbon and nutrient cycling.

Examples: Amoebae (e.g., Amoeba proteus), ciliates (e.g., Paramecium, Tetrahymena), and social amoebae (Dictyostelium) perform phagocytosis. Some other protists and many immune cells employ phagocytic feeding in metazoans.

Evolution and diversity: Phagocytosis is an ancient cellular process associated with the development of phagocytic vacuoles and lysosomes; its evolutionary origins are linked to the emergence of endomembrane systems and diverse food acquisition strategies across lineages.