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 plan t residues and may be involved in allelopathic interactions. We isolated ba cteria from the recirculating nutrient solution of a closed, hydroponic let tuce 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 m u M. Isolates p208, p210 and p307 showed the highest degradation rates and were therefore used for single- and multiple-strain inoculation in two fact orial experiments where lettuce (Lactuca sativa L. cv. Grand Rapids) plants were grown gnotobiotically for 2 weeks in nutrient solution with or withou t 200 mu M 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 signific ant effects of the bacterial treatments could be found with respect to plan t dry weight. However, in the presence of FA, isolate p210 increased shoot dry weight and the multiple-strain treatment increased root and shoot dry w eights in the first experiment. In the second experiment, isolate p210 neit her affected the concentration of FA nor plant dry weights. Isolate p208 an d the multiple-strain treatment reduced the negative effect of FA on latera l root lengths and root hair formation in both experiments. Finally, we con clude that bacteria with the capacity to degrade FA and to ameliorate phyto toxic effects of FA were present in the nutrient solution of a commercial h ydroponic lettuce culture. (C) 2000 Elsevier Science Ltd. All rights reserv ed.