Bacterial Chemotaxis Enhances Naphthalene Degradation in a Heterogeneous Aqueous System

Chemotaxis has the potential to enhance the bacterial degradation of organic pollutants in systems in which the pollutants are distributed heterogeneously. However, experimental evidence to confirm this potential has not been documented. In the present study, we evaluated the role of chemotaxis in naphthalene degradation by Pseudomonas putida G7 (PpG7) in aqueous systems that supplied naphthalene from a glass capillary tube. Wild-type PpG7 degraded naphthalene more rapidly than two mutant strains, one deficient in chemotaxis to naphthalene and the other deficient in motility. This result was not due to differences in inherent naphthalene degradation kinetics, as all three strains degraded naphthalene at similar rates in a well-mixed system. In the heterogeneous system, a 90% reduction in the amount of naphthalene initially present took 6 h with the wild-type PpG7 at an initial concentration of 4 × 106 cfu/mL, while a similar reduction with either mutant strain at the same concentration took approximately 30 h. Only the systems inoculated with the wild-type strain exhibited degradation rates in excess of the rate of naphthalene diffusion from the capillary. This suggests that chemotaxis to a priority pollutant can overcome the mass transfer limitations that may govern biodegradation rates in a number of situations.