Cyclodextrin-enhanced degradation of toluene and p-toluic acid by Pseudomonas putida

Abstract

Degradation of an immiscible aromatic solvent, toluene, and a water- soluble aromatic compound, p-toluic acid, by a Pseudomonas putida strain in the presence of β-cyclodextrin (β-CD) was investigated. The ability of CDs to interact with hydrophobic organics and form inclusion compounds was exploited in this study to remove or alleviate the toxicities of substrates and consequently to enable or enhance degradation. Liquid toluene was found to be highly toxic to P. putida. However, this phase toxicity was removed when crystalline β-CD-complexed toluene was provided as the substrate. The latter was fully degraded at a concentration of up to 10 g/liter. Degradation of toluene vapors was enhanced in the presence of β-CD as a result of reduced molecular toxicity and facilitated absorption of the gaseous substrate. Similarly, β-CD alleviated the inhibitory effect of p-toluic acid on P. putida. This protective effect of CD was remarkably more prominent when the microbial culture was shock loaded with an otherwise toxic dose of p- toluic acid (1.8 g/liter).