Potential benefit of microalgae and their interaction with bacteria to sustainable crop production

Agriculture is undergoing a paradigm shift as it moves away from relying only on agrochemicals toward natural-based product to enhance plant growth and productivity while sustainably maintaining soil quality and productivity. In this sense, microalgae and bacteria offer a unique potential due to the growing use of novel and eco-friendly products such as biofertilizers, biostimulants, and biopesticides. Microalgae improve crop growth and health by fixing nitrogen, releasing soil trace elements, solubilizing potassium, and phosphorus, producing exopolysaccharides, and converting organic matter into utilizable nutrients. They also release bioactive substances including, carbohydrates, proteins, enzymes, vitamins, and hormones, to promote plant growth, control pests, and mitigate plant stress responses. Even though it has long been known that microalgae produce various bioactive and signaling molecules (like phytohormones, polysaccharides, lipids, carotenoids, phycobilins, and amino acids) which are effective in crop production, the targeted applications of these molecules in plant science are still in the very early stages of development. Microalgae are beneficial to bacteria because they produce oxygen and extracellular chemicals, and bacteria, in turn, provide microalgae with carbon dioxide, vitamins, and other nutrients in exchange. This review discusses the possible role of microalgae in increasing crop yield, protecting crops, and maintaining soil fertility and stability, and it points out that interactions of microalgae and bacteria may have a better enhancement of crop production in a sustainable way than using either of them alone.