Bacterial amelioration of ferulic acid toxicity to hydroponically grown lettuce (Lactuca sativa L.)

Ferulic acid (FA) is released from plant roots and by decomposition of plant residues and may be involved in allelopathic interactions. We isolated bacteria from the recirculating nutrient solution of a closed, hydroponic lettuce culture using nutrient media supplemented with 1.0 mM FA. The isolates were tested for their capacity to degrade FA in concentrations up to 200 μM. Isolates p208, p210 and p307 showed the highest degradation rates and were therefore used for single- and multiple-strain inoculation in two factorial experiments where lettuce (Lactuca sativa L. cv. Grand Rapids) plants were grown gnotobiotically for 2 weeks in nutrient solution with or without 200 μM FA. When isolate p208 or multiple strains were added, no FA was detectable at the end of the experiments. In the absence of FA, no significant effects of the bacterial treatments could be found with respect to plant dry weight. However, in the presence of FA, isolate p210 increased shoot dry weight and the multiple-strain treatment increased root and shoot dry weights in the first experiment. In the second experiment, isolate p210 neither affected the concentration of FA nor plant dry weights. Isolate p208 and the multiple-strain treatment reduced the negative effect of FA on lateral root lengths and root hair formation in both experiments. Finally, we conclude that bacteria with the capacity to degrade FA and to ameliorate phytotoxic effects of FA were present in the nutrient solution of a commercial hydroponic lettuce culture.