Biotransformation of di-n-butyl phthalate by a psychrotrophicPseudomonas fluoresceins(BGW) isolated from subsurface environment

Abstract

A psychrotrophic denitrifying Pseudomonas fluorescens was isolated from an unamended subsurface microcosm incubated at 10 °C for 43 days. This pseudomonad transformed di-n-butyl phthalate at 10 °C in a chemically defined medium under both aerobic and anaerobic conditions using NO3−as the terminal electron acceptor. Biotransformation of di-n-butyl phthalate by the pseudomonad appeared to take place only in the stationary and decline phases of growth and was correlated to the amount of biomass. Studies with growth inhibitors and outer membrane permeabilizers suggested that the outer membrane of the cells in the stationary and decline phases was possibly made more permeable to di-n-butyl phthalate, which would explain the biotransformation pattern. Butanol was produced and utilized by cells that transformed di-n-butyl phthalate, implying that the side chains were hydrolyzed by means of an esterase. An esterase was detected by staining after isolation by gel electrophoresis. The esterase was not induced by di-n-butyl phthalate and was present at various stages of growth. The isolated pseudomonad did not grow with phthalic acid as the sole source of carbon, indicating that di-n-butyl phthalate was not mineralized by this bacterium.Key words: biotransformation, di-n-butyl phthalate, psychrotroph, pseudomonad.