Interaction of the antibiotic norfloxacin with ionic micelles: pH-dependent binding

The interaction of the antimicrobial drug norfloxacin (NFX) with anionic sodium dodecyl sulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) micelles was studied using the intrinsic spectroscopic properties of NFX to obtain association constants and molecular modifications. Nonionic Tween^® 20 micelles were also investigated, but the spectroscopic properties of NFX did not detect interactions with these micelles, and quenching by iodide suggested a weak association constant around 47 M^?1. For SDS and CTAB, UV–Vis absorption spectroscopy, steady-state and time-resolved fluorometry were monitored as a function of surfactant concentration ranging from the premicellar to micellar region. It was found that cationic (pH 4.0) and zwitterionic NFX (pH 7.4) associate with SDS micelles, with binding constants equal to 5.4 × 10³ and 1.7 × 10³ M^?1, respectively. Premicellar interaction slightly decreases the critical micelle concentration of SDS. Association of anionic NFX (pH 10.6) is very weak. The fluorescence spectrum and lifetime showed that SDS-associated NFX is cationic and that the heterocycle penetrates the interfacial environment of decreased polarity. Cationic CTAB micelles do not bind cationic NFX, and the association constant with zwitterionic NFX is two orders of magnitude lower than that of SDS micelles. From a pharmacological point of view, it is important that at neutral pH, NFX presented a two orders of magnitude higher affinity for anionic than for cationic sites, and did not interact significantly with nonionic or zwitterionic micelle interfaces.     

Influence of Ionic Surfactants on the Microstructure of Heat-Set β-Lactoglobulin-Stabilized Emulsion Gels

Using confocal microscopy, we studied the effect of heating (up to 85°C) on the microstructure of β-lactoglobulin-stabilized emulsions (20 vol% oil, pH 6.8) containing excess protein (total protein content 13.2%). Two different fluorescent dyes were used to separately visualize the oil droplets and the protein. In overlay micrographs, their location with respect to each other could then be determined. In the presence of a low salt concentration, flocculation of the emulsion without surfactant was inhibited, by a mechanism analogous to the “salting-in” of aqueous protein solutions. Addition of the anionic surfactant sodium dodecyl sulfate (SDS) caused weak flocculation, probably as a result of the formation of protein−SDS complexes. The final heat-set emulsion contained distinct pores for a surfactant/protein ratio of R = 1, but no pores for R = 2. Addition of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) caused strong aggregation, as indicated by microscopic observation of the concentrated emulsion and light scattering of the diluted emulsion. For R = 1 with CTAB, there were aggregates consisting of oil droplets and excess protein. At R = 2, almost all the excess protein was aggregated into separate protein flakes. In the final emulsion gels containing CTAB, the protein was more spread out. Differing structural behavior with anionic and cationic surfactants has been interpreted in terms of different protein−surfactant interactions in aqueous solution and at the oil−water interface, both before and after protein denaturation.     

DEVELOPMENT OF GENETICALLY ENCODED FLUORESCENT PROTEIN CONSTRUCTS OF HYPERTHERMOPHILIC MALTOSE-BINDING PROTEIN

Circularly permuted green fluorescent protein (cGFP) was inserted into the hyperthermophilic maltose binding protein at two different locations. cGFP was inserted between amino acid residues 206 and 207, or fused to the N-terminal of maltose binding protein from Thermotoga maritima. The cloned DNA constructs were expressed in Escherichia coli cells, and purified by metal chelate affinity chromatography. Conformational change upon ligand binding was monitored by the increase in fluorescence intensity. Both of the fusion proteins developed significant fluorescence change at 0.5 mM maltose concentration, whereas their maltose binding affinities and optimum incubation times were different. Fluorescent biosensors based on mesophilic maltose binding proteins have been described in the literature, but there is a growing interest in biosensors based on thermostable proteins. Therefore, the developed protein constructs could be models for thermophilic protein-based fluorescent biosensors.     

Surfactant-mediated amyloidogenesis behavior of stem bromelain; a biophysical insight

Neurodegenerative disorders are mainly associated with amyloid fibril formation of different proteins. Stem bromelain (SB), a cysteine protease, is known to exist as a molten globule state at pH 10.0. It passes through the identical surrounding (pH 10.0) in the gut epithelium of intestine upon oral administration. Protein–surfactant complexes are widely employed as drug carriers, so the nature of surfactant toward protein is of great interest. The present work describes the effect of cationic surfactants (CTAB & DTAB) and their hydrophobic behavior toward amyloidogenesis behavior of SB at pH 10.0. Multiple approaches including light scattering, far UV-CD, turbidity measurements, and dye binding assay (ThT, Congo red and ANS) were performed to measure the aggregation propensity of SB. Further, we monitored the hydrodynamic radii of aggregates formed using dynamic light scattering technique. Structure of fibrils was also visualized through fluorescence microscopy as well as TEM. At pH 10.0, low concentration of CTAB (0–200 μM) induced amyloid formation in SB as evident from a prominent increase in turbidity and light scattering, gain in β-sheet content, and enhanced ThT fluorescence intensity. However, further increase in CTAB concentration suppressed the fibrillation phenomenon. In contrast, DTAB did not induce fibril formation at any concentration used (0–500 μM) due to lower hydrophobicity. Net negative charge developed on protein at high pH (10.0) might have facilitated amyloid formation at low concentration of cationic surfactant (CTAB) due to electrostatic and hydrophobic interactions.     

Fluorescence quenching of beta-carboline alkaloids in micellar media. A study to select the adequate surfactant to use in analytical techniques.

The study of fluorescence quenching of the fluorophores allows the localization of the alkaloids (harmane and harmine) in the micelles (SDS, CTAB, Brij-35) to be established. In aqueous micellar solutions (SDS and Brij-35) at pH 13.0, emission corresponding to the neutral or zwitterionic forms can be observed. In the presence of CTAB (pH = 13.0) it was possible to observe the emission of anionic form. These species are not present in buffered aqueous solutions at these pH values. Bromide ion was added to the different surfactant solutions and the quenching effect was studied according to the Stern-Volmer equation. In the presence of SDS the quenching effect is considerably reduced compared to the aqueous solutions without surfactants, while for Brij-35 micelles were similar to those observed in homogeneous aqueous solution. For CTAB micelles a notable fluorescence quenching was observed for the different pH values studied. The fluorescence quenching studies show that the neutral species are associated inside the micelles, instead of the ionic species (cationic, zwitterionic or anionic) remaining on the surface of the micelles. The anionic surface of SDS micelles prevents the quenching effect by anionic quenchers for both neutral and charged species.     

Conformational and phase transitions in DNA—photosensitive surfactant solutions: Experiment and modeling

DNA binding to trans‐ and cis‐isomers of azobenzene containing cationic surfactant in 5 mM NaCl solution was investigated by the methods of dynamic light scattering (DLS), low‐gradient viscometry (LGV), atomic force microscopy (AFM), circular dichroism (CD), gel electrophoresis (GE), flow birefringence (FB), UV–Vis spectrophotometry. Light‐responsive conformational transitions of DNA in complex with photosensitive surfactant, changes in DNA optical anisotropy and persistent length, phase transition of DNA into nanoparticles induced by high surfactant concentration, as well as transformation of surfactant conformation under its binding to macromolecule were studied. Computer simulations of micelles formation for cis‐ and trans‐isomers of azobenzene containing surfactant, as well as DNA‐surfactant interaction, were carried out. Phase diagram for DNA‐surfactant solutions was designed. The possibility to reverse the DNA packaging induced by surfactant binding with the dilution and light irradiation was shown. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 109–122, 2015.     

Time-resolved fluorescence and circular dichroism of porphyrin cytochrome c and Zn-porphyrin cytochrome c incorporated in reversed micelles

Interactions between fluorescent horse heart cytochrome c derivatives (e. g. porphyrin cytochrome c and Zn-porphyrin cytochrome c) with surfactant interfaces in reversed micellar solutions have been studied, using different spectroscopic techniques. Anionic [sodium bis(2-ethylhexyl)sulfosuccinate, AOT] and cationic (cetyltrime-thylammonium bromide, CTAB) surfactant solutions have been used in order to investigate the effects of charge interactions between proteins and interfaces. Circular dichroism reveals that much of the protein secondary structure is lost in AOT-reversed micelles, especially when the molar water/surfactant ratio, wo, is high (wo = 40), whereas in CTAB-reversed micelles secondary structure seems to be preserved. Time-resolved fluorescence measurements of the porphyrin in the cytochrome c molecule yields information about the changes in structure and the dynamics of the protein upon interaction with surfactant assemblies both in aqueous and in hydrocarbon solutions. With AOT as surfactant a strong interaction between protein and interface can be observed. The effects found in aqueous AOT solution are of the same kind as in hydrocarbon solution. In the CTAB systems the interactions between protein and surfactant are much less pronounced. The measured effects on the fluorescence properties of the proteins are different in aqueous and hydrocarbon solutions. In general, the observations can be explained by an electrostatic attraction between the overall positively charged protein molecules and the anionic AOT interface. Electrostatic attraction can also occur between the cytochrome c derivatives and CTAB because there is a negatively charged zone on the surface of the proteins. From the fluorescence anisotropy decays it can be concluded that in the CTAB-reversed micellar system these interactions are not important, whereas in an aqueous CTAB solution the proteins interact with surfactant molecules.     

Interaction between covalent DNA gels and a cationic surfactant

The interaction of covalently cross-linked double-stranded (ds) DNA gels and cetyltrimethylammonium bromide (CTAB) is investigated. The volume transition of the gels that follows the absorption of the oppositely charged surfactant from aqueous solution is studied. As do other polyelectrolyte networks, DNA networks form complexes with oppositely charged surfactant micelles at surfactant concentrations far below the critical micelle concentration (cmc) of the polymer-free solution. The size of the absorbed surfactant aggregates is determined from time-resolved fluorescence quenching (TRFQ). At low surfactant concentrations, small discrete micelles (160 < N < 210) are found, whereas large micelles (N > 500) form at surfactant concentrations of 1 mM. When the DNA is in excess of the surfactant, the surfactant binding is essentially quantitative. The gel volume decreases by 90% when the surfactant to DNA charge ratio, beta, increases from 0 to 1.     

Use of nile red as a fluorescent probe for the study of the hydrophobic properties of protein-sodium dodecyl sulfate complexes in solution.

Our results show that the noncovalent dye 9-diethylamino-5H-benzo[alpha]phenoxazine-5-one (Nile red) can be used as a fluorescent probe to study the hydrophobic properties of proteins associated with the anionic detergent sodium dodecyl sulfate (SDS). Nile red can interact with both SDS micelles and protein-SDS complexes. The enhancement of Nile red fluorescence observed with diverse types of proteins occurs at SDS concentrations lower than the critical micelle concentration of this detergent. This is also observed using the covalent fluorophore rhodamine B isothiocyanate. Additional results obtained in studies in solution show that the fluorescence intensity and the spectral characteristics of Nile red associated with different proteins complexed with SDS are very similar. These spectroscopic similarities are probably related to the equivalent synchrotron X-ray scattering results found for various protein-SDS complexes in solution. The scattering results suggest that SDS induces the formation of complexes in which the basic structural properties are independent of the different initial structures of native proteins. We speculate that Nile red is bound to regions with equivalent hydrophobic characteristics located in the uniform structures produced by the association of SDS with proteins.     

Hydrophobic tail length plays a pivotal role in amyloid beta (25–35) fibril–surfactant interactions

The amyloid β‐peptide fragment comprising residues 25–35 (Aβ_25‐35) is known to be the most toxic fragment of the full length Aβ peptide which undergoes fibrillation very rapidly. In the present work, we have investigated the effects of the micellar environment (cationic, anionic, and nonionic) on preformed Aβ_25‐35 fibrils. The amyloid fibrils have been prepared and characterized by several biophysical and microscopic techniques. Effects of cationic dodecyl trimethyl ammonium bromide (DTAB), cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic polyoxyethyleneoctyl phenyl ether (Triton X‐100 or TX) on fibrils have been studied by Thioflavin T fluorescence, UV–vis spectroscopy based turbidity assay and microscopic analyses. Interestingly, DTAB and SDS micelles were observed to disintegrate prepared fibrils to some extent irrespective of their charges. CTAB micelles were found to break down the fibrillar assembly to a greater extent. On the other hand, the nonionic surfactant TX was found to trigger the fibrillation process. The presence of a longer hydrophobic tail in case of CTAB is assumed to be a reason for its higher fibril disaggregating efficacy, the premise of their formation being largely attributed to hydrophobic interactions. Proteins 2016; 84:1213–1223. © 2016 Wiley Periodicals, Inc.     

Fluorimetric studies on the binding of 4-(dimethylamino)cinnamic acid with micelles and bovine serum albumin

The constrained photophysics of intramolecular charge transfer (ICT) probe 4-(dimethylamino)cinnamic acid (DMACA) was studied in different surfactant systems as well as in presence of model water soluble protein bovine serum albumin (BSA). Binding of the probe in ionic micelles like sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) causes an increase in ICT fluorescence intensity, whereas, in non-ionic TritonX-100 (TX-100) the intensity decreases with a concomitant increase in emission from locally excited (LE) state. The observations were explained in terms of the different binding affinity, location of the probe and also the nature of specific hydrogen bonding interaction in the excited state nonradiative relaxation process of DMACA. The ICT fluorescence emission yield decreases in BSA due to the locking in of the probe buried in the hydrophobic pocket of the protein structure. SDS induced uncoiling of protein and massive cooperative binding between BSA and SDS is manifested by the release of probe molecules in relatively free aqueous environment.     

Symmetric and asymmetric squarylium dyes as noncovalent protein labels: a study by fluorimetry and capillary electrophoresis

Noncovalent interactions between two squarylium dyes and various model proteins have been explored. NN127 and SQ-3 are symmetric and asymmetric squarylium dyes, respectively, the fluorescence emissions of which have been shown to be enhanced upon complexation with proteins such as bovine serum albumin (BSA), human serum albumin (HSA), beta-lactoglobulin A, and trypsinogen. Although these dyes are poorly soluble in aqueous solution, they can be dissolved first in methanol followed by dilution with aqueous buffer without precipitation, and are then suitable for use as fluorescent labels in protein determination studies. The nature of interactions between these dyes and proteins was studied using a variety of buffer systems, and it was found that electrostatic interactions are involved but not dominant. Dye/protein stoichiometries in the noncovalent complexes were found to be 1:1 for SQ-3, although various possible stoichiometries were found for NN127 depending upon pH and protein. Association constants on the order of 10(5) and 10(7) were found for noncovalent complexes of SQ-3 and NN127, respectively, with HSA, indicating stronger interactions of the symmetric dye with proteins. Finally, HSA complexes with NN127 were determined by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). In particular, NN127 shows promise as a reagent capable of fluorescently labeling analyte proteins for analysis by CE-LIF without itself being significantly fluorescent under the aqueous solution conditions studied herein.     

Spectroscopic and interfacial properties of myoglobin/surfactant complexes

The complexes of horse myoglobin (Mb) with the anionic surfactant sodium dodecyl sulfate (SDS), and with the cationic surfactants cetyltrimethylammonium chloride (CTAC) and decyltrimethylammonium bromide (DeTAB), have been studied by a combination of surface tension measurements and optical spectroscopy, including heme absorption and aromatic amino acid fluorescence. SDS interacts in a monomeric form with Mb, which suggests the existence of a specific binding site for SDS, and induces the formation of a hexacoordinated Mb heme, possibly involving the distal histidine. Fluorescence spectra display an increase of tryptophan emission. Both effects point to an increased protein flexibility. SDS micelles induce both the appearance of two more heme species, one of which has the features of free heme, and protein unfolding. Mb/CTAC complexes display a very different behavior. CTAC monomers have no effect on the absorption spectra, and only a slight effect on the fluorescence spectra, whereas the formation of CTAC aggregates on the protein strongly affects both absorption and fluorescence. Mb/DeTAB complexes behave in a very similar way as Mb/CTAC complexes. The surface activity of the different Mb/surfactant complexes, as well as the interactions between the surfactants and Mb, are discussed on the basis of their structural properties.     

On the mechanism of SDS‐induced protein denaturation

To understand the mechanism of ionic detergent‐induced protein denaturation, this study examines the action of sodium dodecyl sulfate on ferrocytochrome c conformation under neutral and strongly alkaline conditions. Equilibrium and stopped‐flow kinetic results consistently suggest that tertiary structure unfolding in the submicellar and chain expansion in the micellar range of SDS concentrations are the two major and discrete events in the perturbation of protein structure. The nature of interaction between the detergent and the protein is predominantly hydrophobic in the submicellar and exclusively hydrophobic at micellar levels of SDS concentration. The observation that SDS also interacts with a highly denatured and negatively charged form of ferrocytochrome c suggests that the interaction is independent of structure, conformation, and ionization state of the protein. The expansion of the protein chain at micellar concentration of SDS is driven by coulombic repulsion between the protein‐bound micelles, and the micelles and anionic amino acid side chains. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 186–199, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Microstructures formed in aqueous solutions of a hydrophobically modified nonionic cellulose derivative and sodium dodecyl sulfate: a fluorescence probe investigation

The association behavior of hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC) and its interaction with the anionic surfactant sodium dodecyl sulfate (SDS) has been studied in the dilute concentration regime. Steady-state fluorescence probe techniques have been utilized to obtain microstructural information of the system properties and combined with macroscopic bulk information from equilibrium dialysis experiments in order to determine binding isotherms of SDS to HM-EHEC. HM-EHEC was found to self-associate and form polymeric micelles in semi-dilute aqueous solutions. c^* for the self-association process was determined to be approximately 0.4%. The microviscosity of the polymeric micelles is much higher, and the micropolarity slightly higher, than that of ordinary SDS micelles. The onset of interaction between HM-EHEC and SDS was evidenced by a simultaneous strong increase in microviscosity and decrease in micropolarity upon successive addition of SDS. There is a minor, noncooperative SDS binding to the HM-EHEC starting from low concentrations of SDS (<5 mM) followed by a highly cooperative binding region at SDS concentrations ≥5 mM. The polymer–surfactant aggregates are rigid and hydrophobic with a maximum in microviscosity in the noncooperative binding region at a very low degree of SDS-adsorption.     

Physico-chemical studies of micelle formation on sepia cartilage collagen solutions in acetate buffer and its interaction with ionic and nonionic micelles. Hydrodynamic and thermodynamic studies

Sepia cartilage collagen (pepsin-extracted) in acetate buffer (pH = 2.98) forms micelles at a particular concentration below which they do not normally form. The critical micelle concentration (cmc) of the collagen was determined in buffer as well as in SDS, cetyltrimethylammonium bromide (CTAB) and Tween-80 micellar environments at different temperatures. Mutual interaction of collagen micelles with the ionic and nonionic micelles through the formation of the mixed micelle concept has also been found. The cmc of collagen decreased in the presence of SDS and Tween-80 micelles whereas it increased in the presence of CTAB micelles. This clearly suggests that the micelle formation of collagen is facilitated by the presence of SDS and Tween-80 and hindered by CTAB micelles. The various thermodynamic parameters were estimated from viscosity measurements and the transfer of collagen into the micelles of various surfactants and the reverse phenomenon was analyzed. This analysis has also been modelled conceptually as a different phase and the results have supported the above phenomenon. Our thermodynamic results are also able to predict the exact denaturation temperature as well as the structural order of water in the collagen in various environments. The hydrated volumes, Vh, of collagen in the above environments and intrinsic viscosity were also calculated. The low intrinsic viscosity, [eta], of collagen in an SDS environment compared to buffer and other surfactant environments suggested more workable systems in cosmetic and dermatological skin care preparations. The one and two-hydrogen-bonded models of this collagen in various environments have been analyzed. The calculated thermodynamic parameters varied with the concentration of collagen. The change of thermodynamic parameters from coil-coil to random-coil conformation upon denaturation of collagen were calculated from the amount of proline and hydroxyproline residues and compared with viscometric results. Thermodynamic results suggest that the stability of the collagen in the additive environments is in the following order: SDS greater than Tween-80 greater than buffer greater than CTAB.     

Fluorescence lifetime and rotational correlation time of bovine serum albumin-sodium dodecyl sulfate complex labeled with 1-dimethylaminonaphthalene-5-sulfonyl chloride: Effect of disulfide bridges in the protein on these fluorescence parameters

A fluorescent dye, 1-dimethylaminonaphthalene-5-sulfonyl chloride, was used to label bovine serum albumin (BSA), intact and disulfide bridges-cleaved. The fluorescence lifetime and fluorescence anisotropy of the adducts in sodium dodecyl sulfate (SDS) solutions were studied by the nanosecond fluorescence depolarization method. The volume of equivalent sphere (V _e) was calculated to be 2.1×10^–19 cm³ for BSA with the intact disulfide bridges from the rotational correlation time. The value ofV _e was 4.4×10^–19 cm³ for the disulfide bridges-cleaved BSA. With an increase in SDS concentration, the rotational correlation time of the intact BSA became longer, while that of the disulfide bridges-cleaved BSA became shorter. This suggests that upon the binding of SDS, the total volume of the intact BSA increases while the expanded state of the protein, caused by the cleavage of the disulfide bridges, becomes compact.     

Photophysical and photodynamic properties of Pyronin Y in micellar media at different temperatures

In this study, photophysics and photodynamical properties of Pyronin Y (PyY) in different liquid media were investigated. Interactions of PyY, which is a positively charged pigment compound pertaining to the xanthene derivatives with surfactants possessing distinct charges, were determined by using the molecular absorption and fluorescence spectroscopy techniques. It was observed that band intensities of absorption and fluorescence spectra belonging to PyY increase in proportion to the water when compared to three micelle systems, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X‐100 (TX‐100). This suggests that interactions in micelle systems are different from those in deionized water, and solvation and surface interactions modify. It is determined that the strongest interaction occurs between PyY dye and SDS, anionic surfactant, and this interaction arises from the electrostatic forces. Calculated photophysical parameters indicated that the microenvironment of PyY in SDS micelle is different to that of other systems. In temperature studies, it was reported that increasing the temperature of the samples increased non‐radiative transitions. Steady‐state fluorescence anisotropy values were calculated by using fluorescence intensities of PyY compound in pre‐micellar, micellar and post‐micellar systems. Once the PyY fluorescence probe is added to the surfactant containing solutions below the critical micelle concentrations, the measured anisotropy values were found to be low because the probe remains in the deionized water phase. When the surfactant concentration of the medium becomes closer to the critical micelle concentrations, the steady‐state anisotropy value prominently increases. This is because of the restrictions on the rotational diffusion of the probe in micellar solution. It is observed that positively charged PyY shows a higher affinity to the negatively charged SDS compared with the positively charged CTAB and neutral TX‐100 surfactants. This can be explained by Coulombic interactions.     

Enhanced separation and detection of serum bilirubin species by capillary electrophoresis using a mixed anionic surfactant—protein buffer system with laser-induced fluorescence detection

The four major bilirubin species in serum are separated by capillary electrophoresis and detected using laser-induced fluorescence detection. The optimum buffer system consists of 40 mM sodium dodecyl sulfate (SDS)—0.012 mM bovine serum albumin (BSA). The use of the SDS—BSA mixture in the mobile phase allows for the separation of four major bilirubin species at physiological pH with untreated capillaries. The results show that the use of BSA as a run buffer modifier in SDS solution improves separation efficiency and increases sample solubility via pH changes of the run buffer. The limits of detection for the bilirubin species using laser-induced fluorescence are between 30 and 150 nM, depending on the bilirubin species; not only is this approximately two orders of magnitude lower than with visible-light absorption methods, it allows the bilirubin species in normal sera to be quantitatively measured without sample pretreatment.     

DETERMINATION OF METHYLENE BLUE BIOSORPTION BY Rhizopus arrhizus IN THE PRESENCE OF SURFACTANTS WITH DIFFERENT CHEMICAL STRUCTURES

Methylene blue (MB) biosorption properties of Rhizopus arrhizus were investigated in the presence of surfactants. The effects of cationic and anionic surfactants on MB removal by dead biomass (1 g L^?1) were determined. MB removal was tested as a function of initial pH (2–12), contact time (5–1440 min), and dye (37.4–944.7 mg L^?1) and surfactant (0–10 mM) concentrations. The opposite charged anionic surfactant dodecylbenzenesulfonic acid sodium salt (DBS) enhanced sorption of cationic MB by biomass dramatically. Maximum biosorption capacity was 471.5 mg g^?1 at pH 8 with 0.5 mM DBS at 944.7 mg L^?1 MB concentration. The surfactant-stimulated fungal decolorization method may provide a highly efficient, inexpensive, and time-saving procedure in biological wastewater treatment technologies.