Bacteria-microalgae interactions from an evolutionary perspective and their biotechnological significance.

Interactions between bacteria and microalgae have been studied in natural environments and in industrial consortia. As results of co-evolution for millions of years in nature, they have developed complex symbiotic relationships, including mutualism, commensalism and parasitism, the nature of which is decided by mechanisms of the interaction. There are two main types of molecular interactions between microalgae and bacteria: exchange of nutrients and release of signalling molecules. Nutrient exchange includes transport of organic carbon from microalgae to bacteria and nutrient nitrogen released from nitrogen-fixing bacteria to microalgae, as well as reciprocal supply of micronutrients such as B vitamins and iron. Signalling molecules such as phytohormones secreted by microalgae and quorum sensing molecules secreted by bacteria have been shown to positively affect growth and metabolism of the symbiotic partner. However, there are still a number of potential microalgae-bacteria interactions that have not been well explored, including cyclic peptides, other quorum signalling molecules, and extracellular vesicles involved in exchange of genetic materials. A more thorough understanding of these interactions may not only result in a deeper understanding of the relationships between these symbiotic organisms but also have potential biotechnological applications. Upon new mechanisms of interaction being identified and characterized, novel bioprocesses of synthetic ecology might be developed especially for wastewater treatment and production of biofertilizers and biofuels.