Fig. 1.

A diagram illustrating different forms of bacteria and microalgae interaction in an open aquatic environment in a) free-living interaction b) phycospheric interaction with the diffusive boundary created between the outside periphery and phycosphere, where the microalga exuded dissolved organic carbon (DOC), while both partners exchange nutrients (nitrogen-N, phosphorus-P, and carbon dioxide-CO₂) with gradient of concentration from the inner part to the periphery, and c) cell-to-cell contact interaction involved in entanglement with bacterial flagella.