Efficient polycyclic aromatic hydrocarbons dihydroxylation in direct micellar systems

Abstract

Optimization of whole-cell bioconversion of the polycyclic aromatic hydrocarbons (PAHs) anthracene, phenanthrene, and naphthalene to the enantiomerically pure corresponding cis-dihydroxydihydro derivatives by the Escherichia coli JM109 (pPS1778) recombinant strain, carrying the naphthalene dioxygenase and corresponding regulatory genes cloned from Pseudomonas fluorescens N3, in micellar systems, is presented. We show that direct microemulsion systems, where a nonionic surfactant such as 1.5% (v/v) Triton X-100 plus 0.6% to 1.0% (v/v) selected oils are able to solubilize the PAHs tested at relatively high concentrations (initial concentrations in the reaction medium > or =10 mM for naphthalene and phenanthrene and > or =2 mM for anthracene), and allow for more efficient substrate bioconversion. These media, while not affecting bacteria viability and performance, provide increased efficiency and final product yields (100% for naphthalene, >30% for anthracene, >60% for phenanthrene). The phase behavior of the direct microemulsion systems for the different substrates and oils utilized was monitored as a function of their volume fraction by light scattering experiments, and related to the bioconversion results. For anthracene and phenanthrene, the dihydroxylated products have an inhibitory effect on the conversion reactions, thus hindering complete turnover of the substrates. We ascertain that such inhibition is reversible because removal of the products formed allowed the process to start over at rates comparable to initial rates. To allow for complete conversion of the PAHs tested a stepwise or continuous separation of the product formed from the micellar reaction environment is being developed.

Bacterial properties changing under Triton X-100 presence in the diesel oil biodegradation systems: from surface and cellular changes to mono- and dioxygenases activities

“…Thus, a special emphasis has been put on an addition of surface active agents to the biological systems (Randazzo et al 2001). These substances can not only increase a very limited water solubility of hydrocarbons (Paria 2008) but also might have an influence on the bacterial surface characteristics (Kaczorek et al 2013a).…”

Biosurfactant-enhanced bioremediation of hydrophobic pollutants

“…A variety of physical, chemical, and biological remediation techniques have been proposed and have been demonstrated to have varying degrees of success [48][49][50]. Surfactants are able to increase hydrophobic substrate solubility and provide a less aggressive environment for bacterial cells [51,52]. Naturally, many microbes are able to degrade PAHs and can produce amphiphatic compounds similar to synthetic surfactants that can form micellar systems [53,54].…”

“…This has been seen in biodegradation improvement in whole-cell bioconversion of naphthalene, phenanthrene, and anthracene by E. coli JM109 recombinant strains carrying naphthalene dioxygenase and regulatory genes cloned from Pseudomonas fluorescens N3 in the presence of surfactants such as Tween 60 and Triton X100. [51,52,55]. We have listed some of the important studies involving biosurfactants and PAHs in the last decade.…”

“…Poor solubility of fluorene is the major problem in biodegradation process leading to the low bioavailability of fluorene as a substrate. It has been recently demonstrated that dilute direct micellar systems formed utilizing nonionic surfactants are able to increase hydrophobic substrate solubility and provide a less aggressive environment for bacterial cells [52,55]. The authors observed that Tween 60 was useful to enhance the fluorene biodegradation rates by R. rhodochrous VKM B-2469 by being an additional carbon source and by decreasing the fluorene toxicity to the bacterial cells.…”

Nonionic Micelles Promote Whole Cell Bioconversion of Aromatic Substrates in an Aqueous Environment

“…The toxicity of the substrates and/or the inhibition exerted by the products should be always considered. 8 On the other side, the relatively low biodegradability of Triton class surfactants and the possible environmental hazard of their metabolites suggests a cautious approach when their use is extended beyond the laboratory scale. 9 The development of genetic engineering techniques has enormously amplified the possibilities of exploitation of bacteria to perform predetermined chemical tasks.…”