Plant growth-promoting rhizobacteria (PGPR) are microorganisms that act in the production of metabolites that confer advantages for the growth and development of the plant, receiving in exchange sources of carbon and energy. Two classic examples of PGPR are rhizobia, which act in the bioavailability of nitrogen, and actinobacteria, which perform numerous functions such as production of phytohormones, antibiotics, and solubilization of phosphate and potassium. To establish this microbiota, the plant releases carbohydrate-rich exudates that not only serve as a carbon source for microorganisms, but also determine which microorganisms can colonize its rhizosphere. This study evaluated how amylase-producing actinobacteria are able to allow rhizobia growth without this enzymatic activity when co-inoculated in a culture medium that has starch as the sole carbon source. Since starch is a carbohydrate like those released in exudates, it is inferred that this ability to facilitate growth in vitro would be important in stimulating rhizobia growth in the rhizosphere and, consequently, nitrogen fixation. Ten actinobacteria and seven rhizobia were used, of which we obtained 12.86% of positive results. This cooperation exemplifies another case of substrate cross-feeding, paving the way to further in vitro and in vivo studies of interbacterial interactions, as well as to the prospect of biofertilizers.
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