Diazotrophyc rhizobacteria isolated from sugarcane can release amino acids in a synthetic culture medium

The active release of amino acids by diazotrophic rhizobacteria into the natural environment or under in vitro conditions is poorly described in the literature. This capacity could be an important trait in the plant-bacteria interaction and in plant growth promotion. The ability of releasing amino acids into a medium free of N-combined was studied in cultures of five diazotrophic genera, Beijerinckia, Burkholderia, Enterobacter, Klebsiella, and Pseudomonas, isolated from the sugarcane rhizosphere. Eleven different amino acids were excreted into the culture media by 40% of the isolates. The highest amino acid diversities were found in Beijerinckia (ICBR 177) and Enterobacter (ICBR 200). The highest quantities were excreted by Beijerinckia (ICBR 177), Enterobacter (ICBR 200), Pseudomonas (ICBR 56), and Klebsiella (ICBR 183). The production of amino acids by rhizobacteria may play an important role in the growth of plants and might also have a direct application in agricultural technologies. The release of amino acids could explain one of the positive effects of plant growth-promoting bacteria and encourage further studies of this subject.