Degradation of Benzene, Toluene and Xylene byPseudomonas aeruginosa Engineered with theVitreoscilla Hemoglobin Gene

Abstract

This study concerns the potential use of Pseudomonas aeruginosa expressing the Vitreoscilla hemoglobin gene for the degradation of important harmful aromatic compounds such as benzene, toluene, and xylene (BTX). The use of these compounds by both strains was determined as the production of cell mass (viable cell number) in a minimal medium containing any one of the BTX compounds as the sole carbon and energy source. Furthermore, the BTX degradation capability of both strains was monitored by measuring the production of 3‐methylcatechol, a common intermediate. For the cells of the logarithmic phase, which were grown at high aeration/high agitation or low aeration/low agitation, the engineered strain showed a better growth rate than the host strain. With the benzene in the medium, the recombinant strain exhibited a higher (up to 4‐fold) cell density than the parental wild‐type strain at this phase. In contrast, regarding the cells of the late stationary phase under high aeration/high agitation conditions, the host strain had generally higher viable cell numbers than the recombinant strain. At this phase this difference was, however, less significant under the conditions of low aeration/low agitation. Similarly, in toluene containing medium (at high aeration/high agitation) the recombinant strain showed a higher cell density which was from a 15‐fold to almost one order of magnitude greater than its parental strain during the logarithmic phase where the cell density of P. aeruginosa remained nearly constant. Contrary to the results with benzene and toluene, both strains exhibited similar growth characteristics when they were grown in the presence of xylene. The positive effect of the oxygen uptake by the recombinant system on the BTX metabolizing activity was also apparent in a high accumulation of 3‐methylcatechol in the cultures of the recombinant strain. At certain points of incubation, the hemoglobin expressing strain showed a significantly (p < 0.05) higher 3‐methylcatechol accumulation than the host strain. These results demonstrated the possible potential of the Vitreoscilla hemoglobin as an efficient oxygen uptake system for the bioremediation of some compounds of environmental concern.

Substrate interactions during the biodegradation of BTEX and THF mixtures by Pseudomonas oleovorans DT4

“…And the colored intermediate in m-xylene biodegradation was not further degraded by strain DT4 in the investigation. These results were in disagreement with the typical m-xylene catabolism pathway where it was transformed by initial oxidation of either methyl group to 3-methylcatechol and further transformed to the citric acid cycle intermediates (Kahraman and Geckil, 2005;Velazquez et al, 2006), but they were extending few earlier observations that an alternative pathway for m-xylene was via direct dioxygenase attack of the aromatic moiety transforming the corresponding cis-dihydrodiol, such as 3,5-dimethylcatechol in m-xylene biodegradation (Smith, 1990). However, the dark color turned out to be a more toxic compound, 2,5-dihydroxybenzaldehyde, by using GC-MS analysis in the degradation of ethylbenzene.…”

Formulation of microbial cocktails for BTEX biodegradation

“…This is because the enriched consortia, which arose by natural selection are not spontaneous in establishing an optimum culture population. Molecular biology approaches enabled the identification of the key genes responsible for BTEX removal and subsequently facilitated the construction of recombinant strains to biodegrade the volatile organics (Lee et al 1994(Lee et al , 1995Kahraman and Geckil 2005). The potential risks associated with the use of these genetically engineered strains, however, hinder their use for practical applications (Díaz 2004).…”

Atomic Force Microscopy Study of the Effect of Lipopolysaccharides and Extracellular Polymers on Adhesion of Pseudomonas aeruginosa

“…Since P. aeruginosa exists naturally in the environment, it is an effective isolate in biodegradation of petroleum hydrocarbons (27,36). P. aeruginosa also causes serious infections, especially in immunocompromised patients; it causes bacteremia in burn victims, bacterial keratitis in soft contact lens users, and chronic lung infections in cystic fibrosis patients (18,33).…”