Surfactant-enhanced Biodegradation Research Articles

Effects of two surfactants on microbial diversity of a PCE-degrading microbial consortium

The effects of two representative surfactants, Rhamnolipids and Tween 80, on the microbial diversity of a PCE-degrading consortium during surfactant-enhanced biodegradation, were explored. The biodegradation efficiency was increased from 47.25% to 73.44%, and 47.25%–66.69%, with the addition of Rhamnolipid at 10 mg/L and Tween 80 at 50 mg/L, respectively. PCE biodegradation kinetics can be described by the pseudo-first-order reaction model for both scenarios. Analyses of alpha and beta indices of the microbial consortium showed that the microbial diversity of both groups exposed to either surfactant was not significantly different from the PCE only group. However, the bacterial abundance in the consortium changed significantly at both the phylum and genus levels. The results demonstrated that the composition of the PCE-degrading consortium is relatively stable, but the exposure to both surfactants results in the enrichment of some genera, which could contribute to the increased biodegradation efficiency.

Properties and potential application of efficient biosurfactant produced by Pseudomonas sp. KZ1 strain

Increasing use of biosurfactants has stimulated the search for new and efficient biosurfactant-producing bacterial strains, preferably nonpathogenic ones. The aim of the present study was to characterize a new isolated Pseudomonas sp. KZ1 strain and its exocellular surface active compounds. After examining several mineral media of different compositions, the bioreactor-scale production of biosurfactants under optimum conditions was tested. Then, the composition of the isolated biosurfactants was investigated by Fourier-transform infrared spectroscopy and gas chromatography-mass spectrometry analysis and their surface active properties were characterized by adsorption parameters. The results indicated that the Pseudomonas sp. KZ1 biosurfactant had the critical micelle concentration of 0.12 g L−1 and decreased the surface tension decreased to 31.7 mN m−1. Moreover, the biosurfactant increased the rate of biodegradation of diesel oil by the strains: Pseudomonas sp. KZ1, Pseudomonas sp. OS4 and Achromobacter sp. KW1. The obtained biosurfactant showing attractive properties is a promising and much ‘greener’ alternative in the application for surfactant-enhanced biodegradation of hydrocarbons.

Surfactant-enhanced biodegradation of crude oil by mixed bacterial consortium in contaminated soil.

This study evaluated the effects of two surfactants (i.e., Tween 80 and SDS) on biodegradation of crude oil by mixed bacterial consortium in soil-aqueous system. The mixed bacterial consortium was domesticated from the activated sludge of cooking plant through a progressive domestication process. High-throughput sequencing analysis revealed that Rhodanobacter sp. was the dominant bacteria. The higher CMCeff value for two surfactants was observed in soil-aqueous system compared with that in aqueous system, which was likely due to their adsorption onto soil particles. Either Tween 80 or SDS can be utilized as carbon source and promote the growth of mixed bacterial consortium. Further findings evidenced that the degradation of crude oil can be enhanced by adding either Tween 80 or SDS. The performance of Tween 80 was generally superior to SDS for the crude oil degradation. The highest crude oil degradation efficiency was 42.2 and 31.0% under the conditions of 5 CMCeff of Tween 80 and 2 CMCeff of SDS, respectively. Furthermore, the degradation efficiency of crude oil in remediation experiment (i.e., 77%) evidenced that the integration of adding Tween 80 and inoculating mixed bacterial consortium was effective for crude oil-contaminated soil decontamination.

Gene expression of an arthrobacter in surfactant-enhanced biodegradation of a hydrophobic organic compound.

Surfactants can affect the biodegradation process and the fate of hydrophobic organic compounds (HOCs) in the environment. Previous studies have shown that surfactants can enhance the biodegradation of HOCs by increasing cell surface hydrophobicity (CSH) and membrane fluidity. In this study, we took this work one step further by investigating the expression levels of three genes of Arthrobacter sp. SA02 in the biodegradation of phenanthrene as a typical HOC at different concentrations of sodium dodecyl benzenesulfonate (SDBS), which is a widely used surfactant. The Δ9 fatty acid desaturase gene codes for Δ9 fatty acid desaturase, which can convert saturated fatty acid to its unsaturated form. The ring-hydroxylating dioxygenase (RHDase) and the 1-hydroxyl-2-naphthoate dioxygenase (1H2Nase) genes code for the RHDase and 1H2Nase enzymes, respectively, which play a key role in decomposing doubly hydroxylated aromatic compounds. The results show that these three genes were upregulated in the presence of SDBS. On the basis of the genetic and physiological changes, we proposed a pathway that links the gene expression with the physiological phenomena, including CSH, membrane fluidity, and intracellular degradation. This study advances our understanding of the surfactant-enhanced biodegradation of HOCs at the gene level, and the proposed pathway should be further validated in the future.

Triphenyltin biosorption, dephenylation pathway and cellular responses during triphenyltin biodegradation by Bacillus thuringiensis and tea saponin

Abstract Triphenyltin is an endocrine disruptor that has polluted the global environment, and thus far, information regarding the mechanisms of triphenyltin biodegradation and cellular metabolic responses is severely limited. The question of whether dephenylation during degradation occurs successively or synchronously is also not clear. Here, these processes were illuminated through experiments involving surfactant-enhanced biodegradation of triphenyltin and its metabolites by Bacillus thuringiensis. Tea saponin significantly enhanced phenyltin solubility, biosorption, membrane permeability, protein expression, cell density and Cl− and PO43− use, reduced intracellular Na+, NH4+, K+ and Mg2+ release, and accordingly increased phenylation biodegradation. Phenyltin biodegradation was initially triggered by benzene ring cleavage, which occurred individually and synchronously, producing diphenyltin, monophenyltin, and tin. After degradation by cells in the presence of 60 mg L−1 tea saponin for 7 d, residual concentrations of triphenyltin, diphenyltin, and monophenyltin were decreased to 283, 270, and 235 μg L−1, respectively.

Partitioning of phenanthrene into surfactant hemi-micelles on the bacterial cell surface and implications for surfactant-enhanced biodegradation

Recent studies have suggested that the ability of a surfactant to enhance the bioavailability of hydrophobic organic compounds (HOC) requires the formation of surfactant hemi-micelles on the bacterial cell surface and subsequent partitioning of HOC into the hemi-micelles. However, the studies did not provide direct evidence of HOC partitioning into surfactant hemi-micelles on the bacterial cell surface. In this study, direct evidence is provided to demonstrate that the nonionic surfactant Brij 30 forms hemi-micelles on the bacterial cell surface and that phenanthrene sorption at the bacterial surface is enhanced by the surfactant. These results are in agreement with the current theory describing surfactant-enhanced HOC bioavailability. This enhanced bioavailability is put into context with microbial kinetics and system partitioning processes, and it is demonstrated that the addition of surfactant can enhance, have no effect, or inhibit HOC biodegradation depending upon surfactant concentration and microbial growth rate. Understanding these non-linear relationships between surfactant-enhanced HOC bioavailability, biodegradation kinetics, and system partitioning will assist in the design and implementation of surfactant-enhanced bioremediation programs.

Relationship between Micellar and Hemi-Micellar Processes and the Bioavailability of Surfactant-Solubilized Hydrophobic Organic Compounds

In a landmark study on surfactant-enhanced biodegradation of hydrophobic organic compounds (HOCs), Guha and Jaffé demonstrated that a fraction (f) of micellar-phase HOC is directly bioavailable to bacterial cells. They developed a theoretical description of fwhich provided an excellent model of the experimental results. However, a mass transfer term describing the transport of the HOC through the cell wall (m(c)) was found to vary over an order of magnitude for the different surfactants examined, and a theoretical description of it remained elusive. This elusivity also resulted in the model not being able to describe a priori why fwas zero for the non-ionic surfactant C12E23. Here, the results of a recent study on surfactant sorption are used to develop an alternative mechanism describing m(c), where hemi-micellar formation on the cell surface is incorporated into the pathway describing micellar HOC bioavailability. The revised model is validated against HOC bioavailability data for five different C12E(y) surfactants, and it is shown that a single value for the mass transfer coefficient describing transfer of the hemi-micellar HOC into the bacterial cell is able to replicate the complete C12E(y) dataset, including that of C12E23 which eluded the original model. Overall, the results indicate that surfactant sorption and hemi-micelle formation are important parameters governing surfactant-enhanced bioavailability.

Surfactant-Enhanced Biodegradation of a PAH in Soil Slurry Reactors

This study focuses on finding operational regimes for surfactant-enhanced biodegradation. Biodegradation of phenanthrene as a model poly cyclic aromatic hydrocarbon (PAH) was studied in soil slurry reactors in the presence and absence of a Triton N-101 surfactant solution. Results showed that the presence of surfactant slowed the initial biodegradation rate of phenanthrene, but increased the total mass of phenanthrene degraded over a four day period by 30%. A mathematical model was developed which simulates the biodegradation of low solubility hydrocarbons in the presence of soils and surfactants by accounting for the hydrocarbon bioavailability in different phases of the system. The model was able to simulate the experimental results using parameters and rate coefficients that were obtained through independent experiments.The model was used to investigate the effect of different operating conditions on the overall biodegradation of phenanthrene. Simulation results showed that there is a system-specific optimum surfactant concentration range, beyond which bioremediation is hindered. The results also indicate that for a given system, the optimal surfactant concentration can be determined from simple sorption and solubility equilibrium experiments. Finally, a metric is presented for determining the potential effectiveness of surfactant-enhanced bioremediation based on the Monod and bioavailability parameters for a given system.

Kinetics of Degradation of Surfactant-Solubilized Fluoranthene by a Sphingomonas paucimobilis

To achieve a better quantitative understanding of the stimulating or inhibiting effect of surfactants on the metabolism of polycyclic aromatic hydrocarbons (PAHs), a biodegradation model describing solubilization, bioavailability, and biodegradation of crystalline fluoranthene is proposed and used to model experimental data. The degradation was investigated in batch systems containing the PAH-degrading bacterium Sphingomonas paucimobilis strain EPA505, the nonionic surfactant Triton X-100, and a fluoranthene-amended liquid mineral salts medium. Surfactant-enhanced biodegradation is complex; however, the biodegradation model predicted fluoranthene disappearance and the initial mineralization well. Surfactant-amendment did increase fluoranthene mineralization rates by strain EPA505; however, the increases were not proportional to the rates of fluoranthene solubilization. The surfactant clearly influenced the microbial PAH metabolism as indicated by a rapid accumulation of colored products and by a surfactan...

Response of fluoranthene-degrading bacteria to surfactants

A prerequisite for surfactant-enhanced biodegradation is that the microorganisms survive, take up substrate and degrade it in the presence of the surfactant. Two Mycobacterium and two Sphingomonas strains, degrading fluoranthene, were investigated for their sensitivity towards non-ionic chemical surfactants. The effect of Triton X-100 and Tween 80 above their critical micelle concentration on mineralization of [14C]-glucose and [14C]-fluoranthene was measured in shaker cultures. Tween 80 had no toxic effect on any of the tested strains. The surfactant inhibited fluoranthene mineralization by the hydrophobic Mycobacterium spp. slightly, but more than doubled that by the two less hydrophobic Sphingomonas strains. Triton X-100 inhibited fluoranthene mineralization by all strains, yet this was more pronounced for the Sphingomonas spp. Both surfactants caused cell wall permeabilization, as shown by transient colouring of surfactant-containing media. Inhibition of glucose mineralization, indicating non-specific toxic effects of Triton X-100, was observed only for the Sphingomonas strains and the toxicity was caused by micelle-to-cell interactions. These strains, however, appeared to recover from initial Triton X-100 toxicity within 50–500 h of exposure. The ratio of surfactant concentration to initial cell density was found to determine critically the bacterial response to surfactants. For both Sphingomonas and Mycobacterium strains, this work indicates that fluoranthene solubilized in surfactant micelles is only partially available for mineralization by the bacteria tested. However, our results suggest that optimal conditions for polycyclic aromatic hydrocarbon mineralization can be developed by selection of the proper surfactant, bacterial strains, cell density and incubation conditions.

Effect of calcium on the surfactant tolerance of a fluoranthene degrading bacterium.

Surfactants are known to increase the apparent aqueous solubility of polycyclic aromatic hydrocarbons (PAHs) and may thus be used to enhance the bioavailability and thereby to stimulate the biodegradation of these hydrophobic compounds. However, surfactants may in some cases reduce or inhibit biodegradation because of toxicity to the bacteria. In this study, toxicity of surfactants on Sphingomonas paucimobilis strain EPA505 and the effect on fluoranthene mineralization were investigated using Triton X-100 as model surfactant. The data showed that amendment with 0.48 mM (0.3 g l-1) of Triton X-100 completely inhibited fluoranthene and glucose mineralization and reduced cell culturability by 100% in 24 h. Electron micrographs indicate that Triton X-100 adversely affects the functioning of the cytoplasmic membrane. However, in the presence of 4.13 mM Ca(2+)-ions, Triton X-100 more than doubled the maximum fluoranthene mineralization rate and cell culturability was reduced by only 10%. In liquid cultures divalent ions, Ca2+ in particular and Mg2+ to a lesser extent, were thus shown to be essential for the surfactant-enhanced biodegradation of fluoranthene. Most likely the Ca(2+)-ions stabilized the cell membrane, making the cell less sensitive to Triton X-100. This is the first report on a specific factor which is important for successful surfactant-enhanced biodegradation of PAHs.

Aqueous Phase Fluorescence Quenching Technique for Measuring Naphthalene Partition Coefficients in Nonionic Surfactant Micelles

A methodology is presented for determining the partition coefficients for polycyclic aromatic hydrocarbons (PAHs) distributed between the aqueous and the micellar pseudophases of nonionic surfactant solutions. The methodology entails measuring total PAH fluorescence and then using varying copper sulfate concentrations to quench the fluorescence contribution from aqueous pseudophase PAH. Additionally, front-surface sample analysis and absorption corrections to counteract inner-filter effects were used to extend the PAH concentration range over which quenching can be used. The methodology was tested by determining the partitioning of a model PAH (naphthalene) when the nonionic surfactant, octaethylene glycol mono-n-dodecyl ether (C 12 E 8 ), was present. Because the aqueous pseudophase is probed, both saturated and unsaturated systems were examined. Thus, the partition measurements are less restricted than those provided by frequently used analyses that must assume the aqueous pseudophase is saturated in order to close the solubilizate mass balance. The value obtained at saturation with naphthalene was in reasonable agreement with the partition coefficient (log K m ) for naphthalene in a similar nonionic surfactant. Moreover, log K m increased from 4.47 at saturation (0.64 mM naphthalene in 1.88 mM surfactant) to 5.03 at 0.057 mM naphthalene (also in 1.88 mM surfactant). In practice, the methodology may prove useful for characterizing partitioning behavior under the varied conditions found in the field, designing surfactant-enhanced biodegradation experiments, and ascertaining the effects of surfactant solubilization on PAH biodegradation rate