Bioavailability of Hydrophobic Compounds Partitioned into the Micellar Phase of Nonionic Surfactants

Abstract

The apparent solubility of polycyclic aromatic hydrocarbon compounds such as phenanthrene can be increased in the presence of surfactants above their critical micelle concentration. A fraction of the phenanthrene partitioned into the micellar phase of some nonionic surfactants can be directly bioavailable to phenanthrene-degrading microorganisms. A model describing the biodegradation of the directly bioavailable micellar-phase substrate is presented. The hypothesis on which the model is based considers the following steps: (a) the contaminant is transported by filled micelles from the bulk solution to the proximity of the cells; (b) the exchange of the filled micelle with the hemimicellar layer around the cell delivers the contaminant to the cell; (c) the contaminant diffuses into the cell and is biodegraded. The biodegradation kinetics were explained in terms of a series of mass-transfer processes, which lead to a similar equation as the Monod kinetics. The theoretically derived expression, describing the micellarphase substrate that is directly bioavailable, includes a series of surfactant dynamics and mass transfer rate parameters that are not readily available or easily determined. A simplified formulation, which can be used to estimate the direct bioavailability of the micellar-phase substrate was therefore obtained and was used to explain experimental observations. The bioavailable fraction of the micellar-phase substrate was independent of the biomass concentration and was a function of the surfactant concentration, the polyoxyethylene chain length of the surfactant, and the biomass surface characteristics.

Isolation of Soil Bacteria Adapted To Degrade Humic Acid-Sorbed Phenanthrene

“…While the cellular characteristic(s) enabling competence is as yet unknown, the presence/absence nature of the phenotype suggests that it was not attributable solely or primarily to characteristics that vary across a continuum (e.g., permeability or cell surface charge). The process underlying competence appeared similar to "direct bioavailability," which referred to the bacterial uptake of a surfactant-sorbed substrate directly from the cores of surfactant micelles (17). Direct bioavailability was suggested based on mineralization kinetics of phenanthrene sorbed by micellar solutions of synthetic, nonionic surfactants (17).…”

“…The process underlying competence appeared similar to "direct bioavailability," which referred to the bacterial uptake of a surfactant-sorbed substrate directly from the cores of surfactant micelles (17). Direct bioavailability was suggested based on mineralization kinetics of phenanthrene sorbed by micellar solutions of synthetic, nonionic surfactants (17). The mechanism by which direct bioavailability occurred was not determined, but it was proposed that uptake occurred from a layer of surfactant hemi-micelles that formed on the cell surface (17).…”

“…Direct bioavailability was suggested based on mineralization kinetics of phenanthrene sorbed by micellar solutions of synthetic, nonionic surfactants (17). The mechanism by which direct bioavailability occurred was not determined, but it was proposed that uptake occurred from a layer of surfactant hemi-micelles that formed on the cell surface (17). A similar process could be envisioned to underlay competence.…”

Use of a whole‐cell biosensor to assess the bioavailability enhancement of aromatic hydrocarbon compounds by nonionic surfactants

“…Once the membrane structure has been altered by the binding of surfactant monomers, the transport of micellarphase compounds into the cell is facilitated by fusion of the micelles with the cell membrane, as hypothesized by Guha and Jaffe (1996b). Evidence for this mechanism has been reported by Miller and Bartha (1989).…”

“…Naphthalene was detected with the diode array UV detector at 220 nm, and phenanthrene was detected using the fluorescence detector with excitation at 280 nm and emission at Hill and Ghoshal (2002). b CMC values from Guha and Jaffe (1996b).…”