cadmium biosorption by a glyphosate-degrading bacterium, a novel biosorbent isolated from...

Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

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JIEC-1879; No. of Pages 7

Cadmium biosorption by a glyphosate-degrading bacterium, a novelbiosorbent isolated from pesticide-contaminated agricultural soils

Elnaz Khadivinia a, Hakimeh Sharafi a, Faranak Hadi a,b, Hossein Shahbani Zahiri a,Sima Modiri a, Azadeh Tohidi a, Amir Mousavi a, Ali Hatef Salmanian a,Kambiz Akbari Noghabi a,*a Department of Molecular Genetics, National Institute of Genetic Engineering and Biotechnology (NIGEB), P. O. Box 14155-6343, Tehran, Iranb Department of Biology, Faculty of Science, Lorestan University, Khoramabad, Iran

A R T I C L E I N F O

Article history:

Received 26 April 2013

Accepted 20 January 2014

Available online xxx

Keywords:

Biosorption

Cadmium

Ochrobactrum sp. GDOS

Glyphosate

A B S T R A C T

In this study, biosorption of cadmium (II) ions from aqueous solutions by a glyphosate degrading

bacterium, Ochrobactrum sp. GDOS, was investigated in batch conditions. The isolate was able to utilize

3 mM GP as the sole phosphorous source, favorable to bacterium growth and survival. The effect of

different basic parameters such as initial pH, contact time, initial concentrations of cadmium ion and

temperature on cadmium uptake was evaluated. The adsorption process for Cd (II) is well fitted with

Langmuir adsorption isotherm. Experimental data were also tested in terms of biosorption kinetics using

pseudo-first-order and pseudo-second-order kinetic models. Maximum metal uptake qmax was obtained

as 83.33 mg g�1. The sorption process of cadmium onto the Ochrobactrum sp. GDOS biomass followed

second-order rate kinetic (R2 = 0.9986). A high desorption efficiency was obtained in pH 2. Reusability of

the biomass was examined under successive biosorption–desorption cycle repeated thrice. The

characteristics of the possible interactions between biosorbent and metal ions were also evaluated by

scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction analysis.

� 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

1. Introduction

Heavy metal contamination in soil and water environments isone of the world’s major environmental problems [1,2]. Industrialwastewaters are usually the source of heavy metals pollution of theenvironment. Many plating and battery industries discharge heavymetals such as chromium, nickel, cadmium and lead in waste-waters. Cadmium is a heavy metal, which causes cancer andserious health hazards through entry into the food chain. It is verymobile in soil and can be transferred to plants and accumulated inthe roots, leaves and stems of plants [3]. A variety of traditionalmethods such as precipitation, coagulation, ion exchange can beused to remove toxic metals from industrial effluents but they areexpensive, relatively inefficient and in most cases they generate agreat amount of waste which is difficult to eliminate [4,5].Recently, increasing interest in the application of a benign methodfor removing heavy metals and dyes from discharging effluentshave resulted in the search for other alternative materials like

* Corresponding author. Tel.: +98 21 4458031; fax: +98 21 44580394.

E-mail addresses: [email protected], [email protected] (K.A. Noghabi).

Please cite this article in press as: E. Khadivinia, et al., J. Ind. Eng. C

1226-086X/$ – see front matter � 2014 The Korean Society of Industrial and Engineer

http://dx.doi.org/10.1016/j.jiec.2014.01.037

those of biological origin [6,7]. In the past few decades, biosorptionusing microbial biomass as an adsorbent has emerged as apotential technique for metal removal, compared to otherprocesses. The biosorption term is a metabolism-independentbinding of heavy metals by dead/inactive biological materials [8]. Areview of literature shows that heavy metals can be removed byinexpensive biological materials such as algae, fungi and bacteria[8,9]. The metal ions in solution are adsorbed on the surface throughinteractions with chemical functional groups such as carboxylate,amine, imidazole, phosphate, hydroxyl and other functional groupsin the cell wall and biopolymers [10]. The biosorption of cadmiumions by different living and dead types of biomass has beenextensively studied [11–14]. Numerous reports have recentlysuggested approaches that use living and nonliving algae foraccumulating or removing heavy metals from aqueous solutions.However, neither the equilibrium nor the kinetic modeling of Cd2+

biosorption by dried Ochrobactrum sp. GDOS has been investigated.Thus, in this work, we studied a glyphosate-degrading bacterialstrain Ochrobactrum sp. GDOS, isolated from farm soil (with at leastfive years history of chemical pesticide glyphosate treatment), as anew sorbent for further studies on equilibrium isotherms andkinetics of cadmium biosorption efficiency.

hem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.01.037

ing Chemistry. Published by Elsevier B.V. All rights reserved.


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E. Khadivinia et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx2

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2. Materials and methods

2.1. Growth and preparation for biosorption

The biosorbent used throughout this study, Ochrobactrum sp.GDOS, was isolated from area on private property in north of Iran,where there was a times gone by herbicide dealing. The isolate wasidentified according to the biochemical and molecular (16S rRNAgene sequence) methods. It was cultured in 5 ml nutrient broth for12 h at 30 8C and 180 rpm. 200 ml of cultures were used toinoculate 500 mL nutrient broth in 2000 mL Erlenmeyer flask andincubated at 30 8C with constant shaking at 180 rpm for 16 h. Thecells was then harvested by centrifugation for 15 min at 7000 rpmand rinsed three times with sterile distilled water and freeze dried.

2.2. Preparation of metal solution

Stock Cd (II) solution of 1000 mg/L was prepared by dissolving2.3709 g CdSO4�8/3H2O (Merck, Germany) in 1000 mL of deionizedwater. Then, the solution was sterilized by autoclaving at apressure of 1.5 atm and a temperature of 121 8C for 10 min.

2.3. Metal biosorption studies

The effect of chemo-physical factors on Cd biosorption such asvarious concentrations of Cd, contact time, temperature and pHwas studied under similar conditions. The biomass (50 mg) wasinoculated to the metal solution with different initial Cd (II)concentrations in the range of 50–350 mg/L at pH 7, and shakenat180 rpm, 30 8C. The effect of contact time (0–360 min),temperature (20–45 8C) and pH (3–8) at optimum Cd concentra-tion was tested. All pH adjustment was made using either reagentgrade HCl or NaOH. The samples were centrifuged and filteredthrough 0.2 mm filter membranes and the cell-free supernatantwas used to estimate the metal ion concentration.

2.4. Analysis of metal ions

The concentration of unadsorbed Cd (II) ions in the biosorptionmedium was determined by using atomic absorption spectropho-tometer (AAS, Varian AA-220, Australia). The amount of Cdsorption onto bacterial biomass was determined from thedifference between the Cd added to the solution and the Cdremaining in the solution after 2 h. Blank samples (withoutbiomass) were also examined to ensure that no adsorption hadtaken place on the walls of the apparatus used. Each experimentwas repeated three times to confirm the results.

The Cd uptake were calculated by using the following Eq. (1):

qe ¼V

mðCi � CeÞ (1)

where qe denotes the specific metal biosorption (mg metal/gbiomass), Ci and Ce are the initial and final Cd concentration (mgmetal/l) in the solution, respectively. V is the volume of aqueoussolution (L) and m is dry weight of biomass for adsorption (g) [15].

2.5. Isotherm studies

The biosorption equilibrium isotherm was obtained by theFreundlich model (Eq. (2)) in addition to the Langmuir model(Eq. (3)). These models can provide information of metal uptakecapacity and difference in metal uptake among various species[16,17].

q ¼ K fCe1=n (2)


where Kf and n are the distribution coefficient and a correctionfactor, respectively. By plotting the linear form of Eq. (2), ln q = 1/nln Ce + ln Kf, the slope is the value of 1/n and the intercept is equalto ln Kf.

qe ¼qmaxbCe

1 þ bCe(3)

where qe is the amount of metal ion adsorbed at equilibriumconcentration, Ce is the equilibrium concentration of metal ionand qmax is the Langmuir constant (mg/g) reflecting thepredicted maximum adsorption capacity of the metal ion perunit weight of biomass to form a complete monolayer on thesurface bound at high Ce. The value of Langmuir constant b

represents a ratio of adsorption rate constant to desorption rateconstant, which also gives an indication of the affinity of themetal for binding sites on the biosorbent. qmax and b can bedetermined from the linear form of Langmuir Eq. (4) by plottingCe/qe vs. Ce [15].

Ce

qe

¼ 1

qmax

þ Ce

qmax

(4)

2.6. Kinetic studies

The kinetics describes the solute uptake, which in turn controlsthe residence time of a sorbate at the solid–solution interface.Many adsorption models have been used to successfully testexperimental biosorption data. Of these, pseudo-first and second-order models have often been used to describe biosorption kineticdata. In order to investigate the mechanism of biosorption of Cd bythe Ochrobactrum sp. GDOS, kinetic models have been used to testexperimental data [16].

The pseudo first-order rate expression based on solid capacity isgenerally expressed as follows:

dqt

dt¼ k1ðqe � qtÞ (5)

where qe and qt are the amount of metal biosorbed per unit weight(mg g�1 dry weight) of biosorbent at equilibrium and at any time t

(min), and k1 is the rate constant of pseudo first-order sorption(min). The integrated form of the above equation after applying theinitial and boundary conditions, for t = 0, qt = 0, becomes:

log ðqe � qtÞ ¼ logqe � k1

2:303 � t(6)

The pseudo-second order kinetic equation is widely used bymany researchers because it always provided a more appropriatedescription than the first order equation [15]. It can be expressed inlinear form:

t

qt

¼ 1

kq2eþ t

qe

(7)

where qt is the amount of sorbate on sorbent at time t (mg g�1),k is the equilibrium rate constant of pseudo-second order sorptionkinetics (g mg�1 min�1) and qe is the equilibrium uptake (mg g�1)[15].

The pseudo first-order and second-order constants weredetermined by plotting log (qe � qt) against t and t/q against t,respectively [17].

2.7. Desorption experiments

Recovery of Cd (II) from the metal-loading biomass was carriedout using desorbant agents such as 0.1 M HCl in a batch system toadjust the pH value to 2.0, 3.0, 4.0 and 5.0, for 2 h, at 30 8C. The



0

5

10

15

20

25

30

35

40

4003002001000

qe(m

g g¹

)

Cd conc entra� on (ppm)

0

5

10

15

20

25

30

35

40

4003002001000

qe(m

g g¹

)

Time (m in)

(a)

(b)

Fig. 1. Effect of cadmium concentration (a) and contact time (b) on biosorption of Cd

by Ochrobactrum sp. GDOS.

E. Khadivinia et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 3

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biomass was separated from eluent solution by centrifugation(7000 rpm, 10 min, at 4 8C) and concentration of the Cd (II)released into the eluent solution was determined. The treatedbiomass was washed with distilled water and then applied inanother sorption cycle. The sorption–desorption experiments wereperformed in thrice. The efficiency of adsorption and desorptionwas determined according to the following equation:

Desorption efficiency ð%Þ ¼ md

mb� 100 (8)

where md is the amount of Cd ions released in the supernatantsolution (mg) and mb represents the metal ions initially adsorbedon the Ochrobactrum sp. GDOS (mg).

2.8. FTIR, XRD and SEM analysis

The Fourier transform infrared spectroscopy (FT-IR, GX 2000)was used to obtain the FT-IR spectra of the biosorbents with andwithout the metal in KBr pellet (sigma). The spectra were in therange of 400–3500 cm�1. The resulting spectra were the average of16 scans. Cell biomass before and after the Cd biosorption testeswas freeze-dried for 24 h and subsequently examined by X-raypowder diffraction (Bruker XRD D8 Advance) coupled with acopper X-ray tube. The scans were collected in a range of 2u from 08to 1108. Scanning electron microscope (SEM) was used to observethe cell-surface morphologic alteration in Cd-loaded Ochrobactrum

sp. GDOS biomass. Metal loaded and metal free biosorbent cellswere fixed with 0.1 M phosphate buffer (pH 7) containing 1%glutaraldehyde for 2 h, washed with distilled water and dehy-drated through a graded ethanol series for 7 min. The finaldehydration process was repeated twice. The dried samples weremounted on stubs and sputter-coated with gold. Micrographs weretaken of specimens by using a SEM instrument (Philips XL30, USA).

2.9. Growth and glyphosate biodegradation by bacterial isolate

The degrading ability of the isolated strains was assayed withbatch cultures in mineral salts medium supplemented withglyphosate (3 mM) by measuring OD600 nm. A 5 ml nutrient brothmedium was inoculated with a single colony of selected isolate andincubated at 30 8C for 12 h as seed culture. The cells were collectedby centrifugation (8500 rpm, 10 min), washed twice with sterileminimal medium and transferred to 250 ml Erlenmeyer flaskscontaining 100 ml of minimal salt medium (MS1) for 48 h withoutany phosphorous source. Hence, bacteria ought to use theindigenous phosphorous. Then, 20 ml of culture were centrifuged(8500 rpm, 10 min) and the cell pellet was inoculated into a 250 mlErlenmeyer flask containing 50 ml of the same fresh mediumcontaining 3 mM GP (OD: 0.1) and incubated at 30 8C for 4 days.

3. Results and discussion

3.1. Characterization of the bacterial isolate

Examination with universal primers for almost fully 16S rRNAsequence alignment revealed that strain GDOS was closely relatedto the genus of Ochrobactrum. The strain GDOS had 97% homologywith the type strain Ochrobactrum ciceri that belongs to a-2subclass of proteobacteria and matches to that of Ochrobactrum

intermedium with a homology of 95%. Considering these values, weclassified strain GDOS into the genus Ochrobactrum and tentativelylabeled our strain Ochrobactrum sp. GDOS, depositing it in GenBankwith the accession number JF831448.


3.2. Metal biosorption studies

A concentration range of cadmium (50–350 mg/L) was desig-nated and examined. The biosorption capacity of the biomassincreased with increasing metal concentration and reached asaturation value. When the concentration increased from 50 to200 mg/L, the loading capacity increased from 9.08 to 34.36.Higher Cd concentrations did not lead to higher biosorptioncapacity. This indicates that at high-level concentrations, theavailable sites of adsorption become fewer and biosorbent sitestake up the available metal more quickly at low concentrations.Accordingly, the biosorption yield is decreased (Fig. 1a).

Contact time is one of the important parameters for biosorptionprocess as it depends on the nature of adsorbent used [19]. Fig. 1bshowed that the rate of metal uptake increased rapidly in the firstpart within 5–30 min of contact. After that, the rate decreases untilwe reach a constant value of metal concentration after 30 min. Thisrepresents the equilibrium time which an equilibrium metal ionconcentration is presumed to have been attained. The dataobtained from this experiment was further used successfully toevaluate the kinetics of the adsorption process. Therefore,maximum biosorption reached after 60 min.

The biosorption results obtained in the present study showedthat no significant changes were observed between the lowest andhighest temperatures studied. Energy-independent mechanismsare less likely to be affected by temperature, since the processesresponsible for biosorption in this case seems to be mainly



0

5

10

15

20

25

30

35

40

50403020100

qe(m

g g¹

)

Temprature (ºC)

0

5

10

15

20

25

30

35

40

45

1086420

qe(m

g g¹

)

Ini�al pH

(a)

(b)

Fig. 2. Effect of temperature (a) and pH values (b) on Cd sorption by Ochrobactrum

sp. GDOS.

Table 1Isotherm and kinetic parameters obtained for the biosorption of Cd by

Ochrobactrum sp. GDOS using the linear method (data calculated by equation of

regression line obtained by software of Excel.2007).

Models Parameters Ochrobactrum

sp. GDOS

Isotherm

Langmuir model qmax (mg g�1) 83.33

R2 0.977

b (mg g�1) 0.0038

Kinetic

Pseudo-second order model qe (mg g�1) 35.46

K2 (mg g�1 min�1) 0.00351

Table 2Comparison of maximum biosorption capacity of cadmium by various biological

sorbents.

Species name Maximum biosorption

capacity (mg g�1)

References

Sargassum sinicola 62.4 [13]

Sargassum lapazeanum 71.2 [13]

Staphylococcus xylosus 250.0 [23]

Fucus spiralis 114.9 [24]

Enterobacter sp. 46.2 [25]

Pseudomonas aeruginosa 42.4 [26]

Pseudomonas putida 8.0 [27]

Streptomyces rimosus 64.9 [28]

Pseudomonas sp. 278.0 [23]

Ochrobactrum sp. GDOS 83.3 Present study


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physico-chemical (electrostatic forces) in nature. In our case, thepossibility to perform the biosorption process at 30 8C makes itmore cost-effective (Fig. 2a).

The result showed that biosorption capacities for metal ionsincreased with an increase in pH until reaching the optimum at pH6.0 for cadmium (Fig. 2b). However, for more than pH 6.0 the metalcations begin to precipitate in case of cadmium. At low pH, cell wallligands were closely associated with the hydronium ions H3O� andrestricted the approach of metal cations as a result of the repulsiveforce. As the pH increased, more ligands such as carboxyl,phosphate, imidazole and amino groups would be exposed andcarried negative charges with a subsequent attraction of metallicions with positive charge and biosorption onto the cell surface.

Table 2 compares maximum cadmium biosorption capacityobtained in this study with some other values reported in theliterature.

3.3. Biosorption isotherm

Sorption isotherm was plotted between the metal uptake (q)and the metal residual concentration in the solution (Ce). Higherregression correlation coefficient for Langmuir than Freundlichmodel (0.977 vs. 0.884, respectively) suggesting that the experi-ment data fitted well with the linearize Langmuir sorption modeland this model is more suitable for describing the biosorptionequilibrium of Cd (II) by Ochrobactrum sp. GDOS in the studiedconcentration range (50–350 mg/L) (Fig. 3a and b). From the slopeand intercept of the straight portion of the plot the values of


Langmiur parameters qmax = 83.33 (mg g�1) and b = 0.0038 werecomputed (Table 1). This suggests that Cd biosorption byOchrobactrum sp. GDOS is more likely to be monolayer sorptionthan heterogeneous surface adsorption. The Langmuir modelassumes uniform energies of adsorption onto the surface of GDOSstrain and no transmigration of the adsorbate.

3.4. Kinetic studies

The sorption kinetics in a biosorption process is significant, as itprovides valuable insights into the reaction pathways and themechanism of a sorption reaction. Pseudo-first and second-ordermodels have been used to predict the best sorption kinetics andalso to obtain the kinetic parameters (Table 1). The low R2 value(0.04) indicated that the uptake data cannot be explained bypseudo-first-order kinetics (Fig. 4a and b). However, data obtainedfrom the kinetic of uptake when modeled with pseudo-second-order equation showed excellent fitting and R2 values are 0.998(Table 1). The results predict the behavior over the entire studyrange, with a chemisorption mechanism involving valency forcesthrough sharing or exchange of electrons between sorbent andsorbate, being the rate controlling step [18].

3.5. Desorption and regeneration

One of the main attractions of biosorption is the potentialability to regenerate the biomass. Desorption using mineral acids isa general method for metal recovery and used for Cu and Znrecovery from Pseudomonas putida [20] or Cd recovery fromgenetically modified E. coli [21]. The result of desorption of Cd (II)ions using HCl (0.1 M) demonstrated that desorption at pH 2.0 wasthe most effective treatment for Cd (II) recovery, being able todesorb more than 97.13% of Cd from Ochrobactrum sp. GDOSbiomass. Desorption at higher pH was not so effective, with a metalrecovery between 91.4 and 76.6% (Fig. 5). Therefore, it is concludedthat the optimal pH for Cd (II) recovery is 2.0.



y = 3.1114 x + 0.012 4R² = 0.977 9

0

0.02

0.04

0.06

0.08

0.1

0.12

0.0350.030.0250.020.0150.010.0050

1/q e

1/Ce

y = 0.653 x + 0.030 6R² = 0.884 7

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

32.521.510.50

Log

q e

Log Ce

(b)

(a)

Fig. 3. The linear form of Langmuir (a) and Freundlich (b) biosorption isotherms of

cadmium by biomass of Ochrobactrum sp. GDOS.

y = -0 .0019x + 0.344 1R² = 0.040 1

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

4003002001000

Log(

q-qt e

)

Time (min)

(a)

y = 0.0282x + 0.2264R² = 0.9986

0

2

4

6

8

10

12

4003002001000

t/q t

Time (min)

(b)

Fig. 4. The linear form of pseudo-first (a) and pseudo-second-order model (b) for Cd

adsorption by lyophilized cell of Ochrobactrum sp. GDOS.


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As shown in Table 3, repeated use of Ochrobactrum sp. GDOSthree times (in sorption–desorption processes) indicated thatrecovery of the Cd (II) adsorbed on the biomass was very efficient.The results demonstrated that solution pH (pH 2.0–4.0) coulddesorb Cd ions with a high percentage in first cycle. The resultsindicated that the biomass could be used repeatedly with highregeneration and metal recovery efficiencies. When comparedtogether, it can be clearly realized that pH 2.0 solutions showed anexcellent performance. In the case of using the solution with a pHof 5.0, there was approximately one-third of difference betweenthe amounts of metal ions sorbed on biomass in the first cycle andit can be assumed unsuitable for reusing of biomass.

3.6. SEM, XRD and FTIR analysis

Scanning electron microscopy (SEM) analysis demonstratedthat the cadmium-loaded cells tend to undergo morphologicalchanges and acquire modified surface characteristics, resulting in

Table 3Sorption performances and desorption efficiency of the Ochrobactrum sp. GDOS.

Cycle number Process qe value (mg g�1) Desorption efficiency (%)

pH 2.0 pH 3.0 pH 4.0 pH 5.0 (a) (b) (c) (d)

(a) (b) (c) (d)

1 (Bio) 40.8 39.6 39.88 39.1 98.6 96.6 96.2 93.5

1 (Des) 40.22 38.25 38.25 36.55

2 (Bio) 41.4 38.6 39.32 37.93 94.7 83.3 82.7 71

2 (Des) 39.2 32.15 32.51 26.93

3 (Bio) 40.09 38.76 39.32 38.12 98.1 94.5 92 65.5

3 (Des) 39.32 36.62 36.17 24.81


the formation of aggregates. This aggregation may indicate thatsurface characteristics of bacteria have been affected by cadmiumexposure. In contrast, untreated cells represent typical appearance(Fig. 6a and b). The crystal phases of Ochrobactrum sp. GDOS cellsbefore and after Cd biosorption were determined by X-ray powderdiffraction (Fig. 7). The XRD profile of the Cd-free Ochrobactrum sp.GDOS cells demonstrated a humped peak between 188 and 288.

Fig. 5. The results of Cd (II) desorption efficiency from Ochrobactrum sp. GDOS

biomass (error bars show standard deviation).



Fig. 6. Scanning electron micrographs (SEM) of Ochrobactrum sp. GDOS cells before

(a) and after (b) cadmium stress.

Fig. 8. Fourier transform infrared spectra (FTIR) of Ochrobactrum sp. GDOS cells

before and after cadmium-loading. Red and blue colors indicate cadmium-loaded

cells and control cells, respectively. (For interpretation of the references to color in

this figure legend, the reader is referred to the web version of this article.)


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But, Cd-loaded cells showed low intensity peak, indicating theamorphous structure of biomass due to Cd stress.

Fig. 8 represents the IR spectrum for the control of bacterialbiomass (Cd free) and biomass after biosorption (Cd ions loaded) in

Fig. 7. X-ray diffraction profiles of dried powdered Ochrobactrum sp. GDOS cells

before and after cadmium-loading. Blue and red colors indicate cadmium-loaded

cells and control cells (without cadmium), respectively. (For interpretation of the

references to color in this figure legend, the reader is referred to the web version of

this article.)


the range of 400–4000 cm�1. The FTIR spectra of the control cellsand Cd-loaded biomass showed the changes in the intensity of thebands at different regions .A peak at 3300 cm�1 corresponds to thestretching bond of the N–H from amino group and indicates abonded hydroxyl group. After the contact with Cd, the cell surfaceexhibited spectra with clear shifts of the N–H and OH stretchingband to lower frequencies, two bands in the region of 2930 and2750 cm�1 corresponds to the symmetrical and asymmetrical –CH– vibrations in lipids. Two strong bands at 1640 and 1540 cm�1

are attributed respectively to the amide I (–CO–) and amide II (–NH–) in proteins. The significant shifts in these peaks indicates thebinding of Cd with amides I and II in cell surfaces of Ochrobactrum

sp. GDOS. A single band near 1440–1445 cm�1 due to the vibrationdeformation d (CH), region of 1205 contains band characteristics ofC–C links and an adsorption bond at the location 1080 cm�1

corresponds to the –CO– group vibrations in the cyclic structures ofcarbohydrates. At the 590 cm�1, there appeared a little change inthe spectra before and after Cd biosorption, demonstrated that P, Scontaining groups contribute in biosorption process. The aboveobservations indicate the involvement of these functional groupssuch as carboxylic, hydroxyl and carbonyl groups of saccharidesand amino groups of proteins in the Cd (II) biosorption process.

3.7. Growth kinetics and glyphosate (GP) degradation

To eliminate endogenous phosphate and increase the efficiencyof GP biodegradation, the phosphorus starved cells was grown inliquid minimal medium with 3 mM GP as the sole phosphoroussource. Complete degradation of GP was observed after 60 h, whichwas faster than the other strains reported by Moneke et al. [22],suggesting that the constitutively expressed enzymes wereinvolved in GP degradation. According to the data obtained fromthe time-course study, GP degradation was parallel to cell growthand began in mid to late exponential phase of growth. However,maximum GP degradation occurred in the early stationary growthphase (data not shown).

4. Conclusions

Despite decades of effort, cadmium contamination of environ-ment has become a worldwide problem, due to the significant useof cadmium in various manufacturing and military industries.Ochrobactrum sp. GDOS, capable of utilizing glyphosate as the solesource of phosphorous, was isolated from agricultural farms innorth of Iran with at least five years history of chemical pesticideglyphosate treatment. Additionally, this bacterium was particu-larly well suited for the removal of cadmium from aqueous




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solutions. The optimal conditions for Cd biosorption wereestablished: 200 mg/L Cd (II) for 2 h at 30 8C and pH 6.0. Themechanism of biosorption includes mainly ionic interactions andformation of complexes between metal cations and acidic sites inthe cell wall of bacterium and this was confirmed by FTIR results.The results demonstrate that Ochrobactrum sp. GDOS could be usedas a promising candidate for glyphosate degradation and cadmiumremoval from aqueous environments.

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