Abstract
We investigated the stability of the phenol-removal ability of an association between Spirodela polyrrhiza and bacteria. We carried out 21-cycle repeated batch experiments (equivalent to 21 days where each cycle was done for 24 hours) on phenol-contaminated water treatment using S. polyrrhiza-pond water bacteria association and pond water bacteria alone. The rate of phenol degradation by the S. polyrrhiza-bacteria association was higher than that by the pond water bacteria alone through the 21 cycles. The phenol degradation ability of the S. polyrrhiza-bacteria association rapidly increased after exposure to phenol, along with a notable increase in the density of catechol 2,3-dioxygenase (C23O) gene in the bacterial community. S. polyrrhiza-bacteria association rapidly gained an enhanced phenol degradation ability compared with the pond water bacteria alone. After phenol acclimation, this enhanced phenol degradation ability of S. polyrrhiza-bacteria association was maintained in the long term, with a high density of catechol 1,2-dioxygenase (C12O) gene and C23O gene in the bacterial community. Bacteria harboring a diverse range of C12O gene and C23O gene accumulated on the root of S. polyrrhiza, and bacterial diversity was stable under conditions of phenol contamination. The findings in this study demonstrate the possibility of using an aquatic plant treatment system as an effective and stable treatment technology for organic pollutants.
