Production of Indole Auxins by <i>Enterobacter</i> sp. Strain P-36 under Submerged Conditions

Abstract

Bioactive compounds produced by plant growth-promoting bacteria through a fermentation process can be valuable for developing innovative second-generation plant biostimulants. The purpose of this study is to investigate the biotechnological potential of Enterobacter on the production of auxin—a hormone with multiple roles in plant growth and development. The experiments were carried in Erlenmeyer flasks and a 2-L fermenter under batch operating mode. The auxin production by Enterobacter sp. strain P-36 can be doubled by replacing casein with vegetable peptone in the culture medium. Cultivation of strain P36 in the benchtop fermenter indicates that by increasing the inoculum size 2-fold, it is possible to reduce the fermentation time from 72 (shake flask cultivation) to 24 h (bioreactor cultivation) and increase the auxin volumetric productivity from 6.4 to 17.2 mg [IAAequ]/L/h. Finally, an efficient storage procedure to preserve the bacterial auxin was developed. It is noteworthy that by sterilizing the clarified fermentation broth by filtration and storing the filtrated samples at +4 °C, the level of auxin remains unchanged for at least three months.

Keywords

• plant biostimulants
• plant growth-promoting rhizobacteria (PGPR)
• <i>Enterobacter</i>
• auxin (IAA)
• organic agriculture