Uroglena americana isolated from Lake Biwa grows photosynthetically only in the presence of bacteria. The ultrastructure of U. americana cell, which was incubated with Escherichia coli for 30 min, indicated that the bacterial cells were engulfed by food vacuoles in the algal cell. This alga was quite unselective in ingesting a variety of food bacteria as well as polystyrene latex particles (0.8 μm). It was confirmed that this alga is a photophagotrophic organism. It was also demonstrated that the bacterial factor essential for the algal growth was phospholipids.