Beyond its established role in agriculture, Azospirillum can enhance the growth and metabolism of photosynthetic organisms such as microalgae. The underlying hypothesis is that Azospirillum, as a non-specific plant growth-promoting bacterium (PGPB), influences green microalgae in a manner similar to higher plants. These effects occur at multiple physiological and metabolic levels, suggesting new applications for A. brasilense. Physiological studies indicate that indole-3-acetic acid (IAA) produced by A. brasilense promotes population growth in several Chlorophyceae species. Metabolic analyses reveal that co-cultivation alters the activity of nitrogen cycle enzymes, including glutamine synthetase and glutamate dehydrogenase, in Chlorella spp, leading to increased nitrogen uptake and intracellular nitrogen accumulation. IAA also enhances ADP-glucose pyrophosphorylase activity, leading to increased starch accumulation, and stimulates acetyl-CoA carboxylase, which in turn increases fatty acid synthesis and total lipid content in the microalgae. A direct exchange of nitrogen and carbon between Azospirillum brasilense Cd and Chlorella sorokiniana was demonstrated using nanoscale secondary ion mass spectrometry (nanoSIMS). In addition, studies have shown that volatile compounds produced by A. brasilense positively affect the growth and metabolism of Chlorella and that riboflavin and lumichrome produced by A. brasilense significantly influence the photosynthetic and auxiliary pigments in microalgae. The combined use of Azospirillum and microalgae has proven effective for wastewater treatment and for restoring desert-degraded soilsSoil after the application of wastewater-derived debris. The following section provides a summary of these findings.