Harnessing the complex microbiota of aquaponic systems for plant growth promotion

Aquaponics is a soilless food production system that sustainably yields plant and fish biomass in a closed loop. It is based on water circulation and beneficial interaction between fish, bacteria, and plants. However, the nutrient flow reaching the plants often presents few available mineralized nutrients. Previous studies have highlighted the existence of a complex microbial network and the presence of potential plant growth-promoting (PGP) bacteria within aquaponic systems. One promising solution to improve nutrient cycling in aquaponics would be to harness such diversity by designing a PGP bacterial consortium. Following a high throughput sequencing (HTS)-guided approach, microbial communities were isolated from aquaponic lettuce (Lactuca sativa L.) rhizoplane and one of our aquaponic facility’s sump and characterized through 16s rDNA amplicon sequencing. A literature-based pre-selection was done to limit the number of candidate bacteria, and a bottom-up approach was followed to design the PGP bacterial consortium. Six beneficial strains were selected based on their expressed PGP traits under in vitro conditions, including phosphate and potassium solubilization, indole-3-acetic acid, and siderophore production. The ability of the strains to live and grow in proximity to each other was assessed through an antagonism test. When used alone, some strains showed promising results by improving the growth of lettuce seedlings. Under aquaponic greenhouse and controlled conditions, lettuce biomass was significantly increased by applying one of the strains. The next steps will be to test the newly designed consortium by assessing its effects on seedlings’ development and the lettuce growth cycle under aquaponic greenhouse conditions.