Bacterial Chemotaxis to Naphthalene Desorbing from a Nonaqueous Liquid

Abstract

Bacterial chemotaxis has the potential to increase the rate of degradation of chemoattractants, but its influence on degradation of hydrophobic attractants initially dissolved in a non-aqueous-phase liquid (NAPL) has not been examined. We studied the effect of chemotaxis by Pseudomonas putida G7 on naphthalene mass transfer and degradation in a system in which the naphthalene was dissolved in a model NAPL. Chemotaxis by wild-type P. putida G7 increased the rates of naphthalene desorption and degradation relative to rates observed with nonchemotactic and nonmotile mutant strains. While biodegradation alone influenced the rate of substrate desorption by increasing the concentration gradient against which desorption occurred, chemotaxis created an even steeper gradient as the cells accumulated near the NAPL source. The extent to which chemotaxis affected naphthalene desorption and degradation depended on the initial bacterial and naphthalene concentrations, reflecting the influences of these variables on concentration gradients and on the relative rates of mass transfer and biodegradation. The results of this study suggest that chemotaxis can substantially increase the rates of mass transfer and degradation of NAPL-associated hydrophobic pollutants.Nonaqueous-phase liquids (NAPLs) pose great challenges in the remediation of contaminated soil and sediment (21, 23). Residual NAPLs are often trapped in pores, leading to smallscale heterogeneity in contaminant distribution and slow rates of contaminant transfer into the surrounding aqueous phase (5, 12, 13). In situ biodegradation by indigenous microorganisms may be a low-cost means of remediating contaminated sites, but its reliability depends on an improved understanding of governing mechanisms (22). One concern is that biodegradation of hydrophobic substrates is often limited by the rate of mass transfer from a nonaqueous phase (1,3,34). Removal of a contaminant from the aqueous phase through biodegradation can, however, improve dissolution of a pure substance or desorption from a nonaqueous phase by increasing the concentration gradient against which mass transfer occurs (3,10,33,37). The rate of mass transfer, and hence the rate of biodegradation, is predicted to increase as the degrading organisms move closer to the contaminant source (3).Chemotaxis by Pseudomonas putida strain G7 was shown recently to enhance the degradation of naphthalene diffusing from a naphthalene-saturated aqueous buffer contained in a capillary (17), consistent with theoretical predictions (2, 15) that bacterial chemotaxis towards nutrient sources can increase the rate of nutrient consumption. The effect of chemotaxis on naphthalene degradation was equivalent to increasing the concentration of nonchemotactic or nonmotile mutant strains by at least two orders of magnitude (27). Unlike the situation in a strictly aqueous system, however, bacteria do not have direct access to the substrate in a nonaqueous source. We therefore examined the effect of chemotaxis on the desorption and biodegradat...

Bacterial Chemotaxis to Atrazine and Relateds-Triazines

“…Chemotaxis, the ability of motile bacteria to detect and respond to specific chemicals, can help bacteria find an optimal niche for their survival and growth and may play a role in the efficient degradation of pollutants in the environment (33,37). Chemotaxis has been shown to enhance naphthalene biodegradation in both a heterogeneous aqueous system (30) and a non-aqueous-phase liquid system (24). In addition, a chemotactic naphthalene-degrading strain caused a higher rate of naphthalene desorption than was observed with nonchemotactic and nonmotile strains (24).…”

“…Chemotaxis has been shown to enhance naphthalene biodegradation in both a heterogeneous aqueous system (30) and a non-aqueous-phase liquid system (24). In addition, a chemotactic naphthalene-degrading strain caused a higher rate of naphthalene desorption than was observed with nonchemotactic and nonmotile strains (24). Pseudomonas sp.…”

Continuous-Flow Capillary Assay for Measuring Bacterial Chemotaxis

“…Suspensions of wild-type, nonmotile, and nonchemotactic (51) Pseudomonas putida G7 were prepared as described previously (45). Briefly, batches of bacterial cultures were grown by lightly scraping a frozen stock (Ϫ70°C) with a sterile wooden applicator stick and transferring the scraping to tryptone broth.…”

Is it possible to increase bioavailability but not environmental risk of PAHs in bioremediation?

“…16 The best studied example of chemotaxis-enhanced bioavailability (and 17 biodegradation) of a PAH relates to the capacity of Pseudomonas putida G7 to degrade 18 naphthalene, and several studies have focused on this strain as a model microorganism. 19 Using a heterogeneous aqueous system under a slow-diffusion regime, the rate of that also used chemotactic and non-chemotactic strains of P. putida G7 clearly 25 demonstrated that chemotaxis increased naphthalene degradation when the compound is 1 present in a non-aqueous-phase liquid (NAPL) [117]. In this case, chemotaxis promoted 2 partitioning and biodegradation of naphthalene by creating a steeper gradient as the cells 3 accumulated near the NAPL/water interface.…”