Chemoeffectors decrease the deposition of chemotactic bacteria during transport in porous media

Bacterial chemotaxis enables motile cells to move along chemical gradients and to swim toward optimal places for biodegradation. However, its potentially positive effects on subsurface remediation rely on the efficiency of bacterial movement in porous media, which is often restricted by high deposition rates and adhesion to soil surfaces. In well-controlled column systems, we assessed the influence of the chemoeffectors naphthalene, salicylate, fumarate, and acetate on deposition of chemotactic, naphthalene-degrading Pseudomonas putida G7 in selected porous environments (sand, forest soil, and clay aggregates). Our data showed that the presence of naphthalene in the pore water decreased deposition of strain G7 (but not of a derivative strain, P. putida G7.C1 (pHG100), nonchemotactic to naphthalene) by 50% in sand-filled columns, as calculated by the relative adhesion efficiency (αt). Similar effects were observed with P. putida G7 strain for the other chemoeffectors. Deposition, however, depended on the chemoeffector's chemical structure, its interaction with the column packing material, and concomitantly its pore-water concentration. As the presence of the chemoeffectors had no influence on the physicochemical surface properties of the bacteria, we suggest that chemotactic sensing, combined with changed swimming modes, is likely to influence the deposition of bacteria in the subsurface, provided that the chemoeffector is dissolved at sufficient concentration in the pore water.The Spanish Ministry of Environment (grants 057/2004/3, 1.2-270/2005/3-B and 392/2006/3-1.2), Spanish Ministry of Education and Science (grant VEM2004-08556), and European Union (QLRT-1999-00326 and EVK1-CT-2001- 00101).Peer Reviewe