The effect of a nonionic and a cationic surfactant, Tween 20 and CTAB, on the
biodegradation rate of fluoranthene and anthracene by a P. putida strain was
investigated. Tween 20 had a positive effect on the biodegradation rate of anthracene.
However, it did not affect significantly fluoranthene oxidation. The cationic surfactant
CTAB inhibited the oxidation of both PAHs, fluoranthene and anthracene

Brito, A. G.

Melo, L. F.

Rodrigues, A. C.

Universidade do Minho: RepositoriUM

Effect of the surfactants tween 20 and CTAB on fluoranthene and anthracene degradation by P. putida

1PAPER N° 190EFFECT OF THE SURFACTANTS TWEEN 20 AND CTAB ONFLUORANTHENE AND ANTHRACENE DEGRADATION BYP. PUTIDAA. C. Rodrigues, A. G. Brito and L. F. MeloCentro de Engenharia Biológica – Instituto de Biotecnologia e Química Fina, Universidade doMinho, 4700 Braga, PortugalABSTRACTThe effect of a nonionic and a cationic surfactant, Tween 20 and CTAB, on thebiodegradation rate of fluoranthene and anthracene by a P. putida strain wasinvestigated. Tween 20 had a positive effect on the biodegradation rate of anthracene.However, it did not affect significantly fluoranthene oxidation. The cationic surfactantCTAB inhibited the oxidation of both PAHs, fluoranthene and anthracene.KEYWORDSBioavailability; polycyclic aromatic hydrocarbons; surfactantsINTRODUCTIONIt has been proposed that the presence of nonionic surfactants at concentrationsabove the critical micelle concentration (CMC) can increase the rate ofbiodegradation of polycyclic aromatic hydrocarbons (PAHs) by solubilization oremulsification (Edwards et al., 1991). On the other hand, surfactants may reducethe adhesion of cells to the hydrocarbon-water interface (Rosenberg andRosenberg, 1995).The ability of surfactants to enhance the bioavalability of PAHs will depend on themechanisms used by bacteria to get access to these hydrophobic substrates.Therefore, the objective of this study is to investigate the effect of the nonionicsurfactant Tween 20 and the cationic surfactant cetyltrimethyl ammonium bromide(CTAB), on the biodegradation rate of fluoranthene and anthracene by aPseudomonas putida strain.METHODS250-mL Erlenmeyer flasks containing 50 mL of a mineral medium withfluoranthene or anthracene as sole substrate (100 mg/L, aproximately), with andwithout added surfactant, were incubated in the dark, at room temperature and 150rpm. The inoculum was a culture of P. putida pregrown on the respective PAH.2Cell growth was assessed by measurements of optical density at 540 nm. Arespirometric technique was used to measure the activity of the cells. Threedifferent concentrations of Tween 20 were tested, 100, 500 e 1000 mg/L. Theeffect of the cationic surfactant CTAB was tested at a concentration of 100 mg/L.RESULTS AND DISCUSSIONFigures 1 and 2 show the results obtained in the respirometric assays.Figure 1 – Activity of P. putida cells using fluoranthene as substrate in thepresence of surfactants.Figure 2 – Activity of P. putida cells using anthracene as substrate in the presenceof surfactants.As can be seen, an increase in the concentration of Tween 20 resulted in a decreasein the activity of the P. putida cells. This result shows that PAHs are less acessibleto microorganisms when higher concentrations of the nonionic surfactant arepresent. It was also observed that growing either on fluoranthene or anthracene,the cell activity at Tween 20 concentrations of 500 and 1000 mg/L was even lowerthan the one obtained when this surfactant was used as sole carbon source (10000,010,020,030,040,050,060,070,08Fluoranthene(100 mg/L)Fl+Tween20(100mg/L)Fl+Tween20(500mg/L)Fl+Tween20(1000mg/L)Tween20(100mg/L)Fl+CTAB(100mg/L)CTAB(100mg/L)Cell activity(mgO2/mgVSS/h)00,010,020,030,040,050,06Anthracene(100 mg/L)Ant+Tween20(100mg/L)Ant+Tween20(500mg/L)Ant+Tween20(1000mg/L)Tween20(100mg/L)Ant+CTAB(100mg/L)CTAB(100mg/L)Cell activity(mgO2/mgVSS/h)3mg/L). Consequently, this result may indicate a toxic effect of Tween 20 atconcentrations higher than 500 mg/L.In the case of fluoranthene, the activity of the cells using this PAH as sole carbonsource was higher than the one obtained in the presence of surfactant. Foranthracene (whose solubility in water is 3.6 times lower than the one offluoranthene), the opposite was observed. Indeed, the cell activity was higherwhen Tween 20 (100 mg/L) was added.Concerning the cationic surfactant CTAB, an activity of the P. putida cells of0.0031 mgO2/mgVSS/h was registered using this surfactant as sole carbon source.However, no cell activity was detected using either fluoranthene or anthracene assubstrate in the presence of CTAB. A possible explanation for this phenomenoncan be the fact that, being a quaternary ammonium compound, CTAB binds bychemisorption to the cell surface of bacteria preventing the direct contact betweenthe PAH and the bacteria.The results of the batch experiments are presented in Figures 3 and 4.Figure 3 – Cell growth on fluoranthene and anthracene with and without Tween 20(100 mg/L).Figure 4 – Cell growth on fluoranthene with and without CTAB (100 mg/L).It was observed that P. putida grows slower on anthracene than on fluoranthene.This result was confirmed by the higher cell activity obtained when fluoranthenewas used as sole carbon source (Figures 1 and 2). The lower water solubitity ofanthracene was certainly the cause for such result. In the case of fluoranthene00,511,522,530 200 400 600 800Time (hours)Abs (540 nm)Fluoranthene Fluoranthene+Tween 20Anthracene Anthracene+Tween 2001230 50 100 150 200 250Time (hours)Abs (540 nm)Fluoranthene Fluoranthene+CTAB CTAB4(Figure 3) the bacteria grew faster, reaching the stationary growth phase morerapidly, when Tween 20 was added. As the stationary growth phase was reached,the cell density was the same with and without added surfactant. Nevertheless, thecell activity obtained when Tween 20 was added was lower than the one observedwithout surfactant (Figure 1). On the other hand, using anthracene as sole carbonsource (Figure 4), the cell density obtained was higher than in the presence ofTween 20. Yet, the activity of the cells was lower (Figure 2). The reason for thisdiscordance is that the bioactivity was monitored during the first 3,5 hours ofgrowth, while the batch experiments were performed within 30 days.The batch experiments performed with CTAB confirmed the results obtained inthe respirometric assays. The fluoranthene oxidation rate decreased to almost zerowhen CTAB was added (Figure 4).CONCLUSIONSThe findings of this study show that the effect of surfactants on the biodegradationof hydrophobic compounds like PAHs depends on the nature and concentration ofthe surfactant and on the PAH itself. In the case of anthracene, the cell activityimproved significantly in the presence of Tween 20 (100 mg/L). However, highercell densities were reached using this PAH as sole carbon source. On the otherhand, Tween 20 did not affect significantly fluoranthene biodegradation.Moreover, the bioactivity was reduced when the surfactant was added, indicating apotential negative effect of the surfactant. Tween 20 concentrations of 500 and1000 mg/L might be toxic to bacteria. The cationic surfactant CTAB inhibitedfluoranthene oxidation.REFERENCESEdwards D.A., Luthy R.G. and Liu Z. (1991). Solubilization of polycyclicaromatic hydrocarbons in micellar nonionic surfactant solutions. Environ. Sci.Technol., 25, 127-133.Rosenberg M. and Rosenberg E. (1995). Bacterial adherence at the hydrocarbon-water interface. Oil Petrochem. Pollut., 2, 155-162.

http://repositorium.sdum.uminho.pt/bitstream/1822/3637/1/Roma-190%5b1%5d.PDF

Effect of the surfactants tween 20 and CTAB on fluoranthene and anthracene degradation by P. putida

Abstract

Similar works

Full text

Available Versions

Universidade do Minho: RepositoriUM

Universidade do Minho: RepositoriUM