Impact of Chemoeffectors on Bacterial Motility, Transport, and Contaminant Degradation in Sand-Filled Percolation Columns.

Chemoeffector-mediated bacterial motility and tactic swimming are major drivers for contaminant accessibility and biodegradation at submillimeter scales. In sand-filled percolated columns we tested how and to what degree chemoeffectors influenced bacterial transport and thereby promoted accessibility and degradation of distantly located 14C-naphthalene (NAH) at the centimeter scale. Sunflower root exudates and silver nanoparticles (AgNPs) were used as chemoeffectors to stimulate opposing effects of motility and tactic swimming of NAH-degrading Pseudomonas putida G7. Sunflower exudates prompted smooth bacterial movement and positive taxis, while AgNPs induced tortuous movement and repellent responses. Compared to chemoeffector-free controls exudates reduced deposition and stimulated bacterial transport during percolation experiments. AgNPs, however, provoked bacterial deposition and concomitant saturation of the collector surfaces (filter blocking) that led to progressively increased percolation of cells. Despite mechanistic differences, both motility patterns supported bacterial transport and promoted mineralization rates of NAH desorbing from a source placed at the column outlet. Observed mineralization rates in the presence of the chemoeffectors were 5-fold higher than those in their absence and similar to NAH-mineralization in well-stirred batch assays. Our results indicate that chemically mediated, small-scale bacterial motility patterns may become relevant for long-distance bacterial transport and the biodegradation of patchy contaminants at higher scales, respectively.