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ROLE OF BACTERIAL STRAINS IN THE PHYTOEXTRACTION OF

CHROMIUM BYPISTIA STRATIOTESANDEICHHORNIA CRASSIPES

Saadia Ijaz; Asma Sadiq; Muhammad Faisal

Department of Microbiology and Molecular Genetics, University of the Punjab, Quaid-e-Azam

Campus, Lahore, Pakistan

Abstract

Chromium is considered to be one of the most toxic heavy metals despite the fact that it is an

essential micronutrient. The present study includes phytoextraction and microbial reduction of Cr

(VI) to Cr (III). For phytoextraction two hydrophytes Pistia stratiotes and Eichhornia crassipes

were selected. Four chromium-resistant bacterial strains: CrS2, CrS3, CrS4 and CrS6 were isolated

from highly polluted industrial sites. Majority of these strains were aerobic, motile, capsule

producing. Two of them were Gram-positive cocci (CrS3) which is also spore former, and

coccobacilli (CrS6). Other two strains were Gram-negative rods (CrS4) and coccobacilli (CrS2).

All the strains were catalase and oxidase positive and two of them have the ability to hydrolyze

starch (CrS3 and CrS6). All the strains supported diverse ranges of pH (5, 7 and 9) and

temperatures (280C, 370C and 450C) and showed multiple resistances to heavy metals (ZnSO4,

CoCl2, CuSO4, MnSO4 and NaSe).The highest resistance shown towards Mn and Se at 2000g ml-1

concentration. Majority of the strains (CrS2, CrS4 and CrS6) were resistant to antibiotics:

Carbencillin, 100g ml-1, Erythromycin 15g ml-1, Ampicillin 25g ml-1, Chloramphenicol 30g

ml-1, Penicillin 10g ml-1 and Novobiocin 5g ml-1, while none of them was able to resist Oxy-

Tetracyclin 30g ml-1. All the strains reduced chromium efficiently within 24 hours under strict

aerobic conditions. Reduction of Cr (VI) increased in the presence of low concentration (50g ml -1)

of different heavy metals. The reduction was also checked with varied concentration of Cr (VI) at


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different pHs (5, 7 and 9) and temperatures (280C, 370C and 450C). The optimal pH and

temperature for reduction was 9 and 45oC respectively. More than one high molecular weight

plasmids were detected in two strains. Increased phytoextraction was done by Pistia stratiotes as

compared with Eichhornia crassipes. When chromium resistant bacteria were used with

hydrophytes, percentage reduction increased.

Keywords: Phytoextraction; Chromium-resistant bacteria; Heavy metal resistance; Hydrophytes;

Pistia stratiotes;Eichhornia crassipes.

Introduction

Wastewaters produced by various industries may contain undesirable amounts of hexavalent

chromium Cr (VI), as chromate and dichromate, a hazardous metal affecting flora and animals of

aquatic ecosystems as well as human health. One removal strategy comprises the microbial

reduction of Cr (VI) to Cr (III), a less soluble chemical species that is less toxic than Cr (VI)

(Caravelli et al; 2008). Water used in industries creates wastewater that has a potential hazard for

our environment (Mahvi et al; 2005). One of the most common polluting heavy metals is chromium

arising from discharged effluents from tanning leather, electroplating, alloy preparation (Ozdemir

et al; 2005).

Naturally occurring Cr is almost exclusively in the trivalent state, as the energy required for its

oxidation is high (Horton et al, 2006). Apart from its toxicity, Cr (VI) is also highly soluble and

thus mobile and biologically available in the ecosystems (Cheung and Gu, 2006). Environmental

problems associated with heavy metals are very difficult to solve in contrast to organic matters

because incineration and biodegradation can transform the latter (Chaalal et al; 2005). Heavy

metals are the natural elements of the earths crust and for that matter they cannot be degraded or

destroyed. Heavy metal is a chemical element that has a specific gravity at least five times that of


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water (Thivierge, 2005). Problems arise when cells are confronted with an excess of vital ions of

heavy metals or with non-nutritional ions that lead to cellular damage (Polle and Schutzenduel,

2003). Natural resources, including plants and microorganisms, have been extensively explored for

their use in metal ion removal from polluted environments (Abou-Shanb et al; 2005; So et al; 2003;

Click, 2003). In bacteria resistance to chromate can be chromosomal borne (Juhnke et al; 2002) or

plasmid mediated (Vitti et al; 2003) or both (Juhnke et al; 2002). The application of

microorganisms to detoxifying metals has been tested in a number of systems, but the viability and

metabolic activity of cells are still the major limiting factors affecting the detoxification efficiency

of the cellular biomass and enzymes involved (Cheung and Gu, 2006).

There are reports on wetland plants like Typha phragmites, Scirpes leersia, Juncus and Spartina in

reducing the levels of heavy metals in polluted water (Deng et al; 2004; Weis and Weis, 2004;

Shankers et al; 2005; Zhang et al; 2007). Until now such emergent hydrophytes have been used in

phytoremediation of effluents in constructing wetland systems but have never been used to reduce

heavy metal pollution in sludge.

For most trace elements, the technique of phytoextraction needs significant improvements to

become practically feasible (Nevel et al; 2007). Phytoremediation offers a cost-effective, non-

intrusive, and safe alternative to conventional cleanup techniques (Zhang, 2007). Phytoremediation

of heavy metals may take one of the several forms: phytoextraction, rhizofiltration,

phytostabilization, and phytovolatilization. Phytoextraction refers to processes in which plants are

used to concentrate metals from the soils into the roots and shoots of the plant.


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Material and Methods

Collection of Hydrophytes

Pistia stratiotes and Eichhornia crassipes plants were selected in sterilized polythene bags from a

freshwater pond of the University of the Punjab, Lahore, Pakistan. The collected plants were

washed with tap water, blot dried and weights of roots and shoots were recorded after that. Plants

were maintained in a growth chamber and were supplied with nutrient solution (Hewitt, 1963) at a

temperature of 2520C with 12 hours photoperiod (10Klux).

Isolation and Characterization Bacterial Strains

Water and soil samples from different polluted industrial sites were collected in sterilized bottles

and polythene bags. Different dilutions of effluents and soil suspensions were made and plated on

nutrient agar (Gerhardt et al; 1994) supplemented with 1000g ml-1 of K2CrO4. The plates were

incubated at 370C for 24 hours and pH 7. Colonies obtained were picked and purified. Isolated

strains were further characterized morphologically (Cheesbrough, 1998), biochemically,

physiologically and genetically.

Physiological characterization

This was done in two ways. Firstly, heavy metal resistance against ZnSO4, CoCl2, CuSO4, MnSO4

and NaSe. For this 5% stock solutions were prepared by dissolving 0.5g of each salt in 10ml

autoclaved distilled water separately and stored at 40C. Isolates were streaked on nutrient agar

supplemented with different concentrations (10g ml-1, 20g ml-1, 50g ml-1, 250g ml-1 and 500g

ml-1

). MnSO4 and NaSe were also checked at a concentration of 1000g ml-1

and 2000g ml-1

. The

plates were incubated at 370C and results were recorded after 24 hours. Secondly, antibiotic

susceptibility against Carbencillin 100g ml-1, Oxy-Tetracyclin 30g ml-1, Erythromycin 15g ml-1,

Ampicillin 25g ml-1, Chloramphenicol 30g ml-1, Penicillin 10g ml-1, Novobiocin 5g ml-1.


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Genetic characterization

This was done by plasmid profiling and agarose gel electrophoresis. Alkaline lysis method is used

for isolating circular plasmid DNA, or even RNA, from bacterial cells (Sambrook and Russell,

2001).

Chromate Reduction Experiments

In this experiment three K2CrO4 initial concentrations (100, 500 and 1000g/ml) were used. For

reduction experiments, DeLeo and Ehrlich (1994) medium was used. Cultures were kept in an

incubating shaker with 150 rpm at three temperatures which were 280C, 370C and 450C. The

reduction was also checked at three different pHs which were 5, 7 and 9. After 24 hours of

incubation, samples were taken aseptically and were analyzed for Cr (VI) reduction. Reduction of

Cr (VI) by bacterial strains was monitored by using the classical spectrophotometric method in the

supernatant of cultures by reacting with Diphenyl Carbazide in solution of phosphoric acid. The

absorption was measured at 540nm.

Effects of Heavy Metal on Cr (VI) Reduction

For this purpose cultures were also separately amended with salts of ZnSO4 50g ml-1, CoCl2 50g

ml-1, CuSO4 50g ml-1, MnSO4 50g ml

-1 and NaSe 50g ml-1 at three different initial

concentrations of Cr (VI) which were: 100, 500 and 1000g ml -1 respectively. The incubation was

given at 450C with pH 7. After 24 hours, cultures were harvested and were processed as mentioned

above to check the amount of Cr (VI) reduced into Cr (III).

Reduction of Cr (VI) to Cr (III) by Pistia stratiotes andEichhornia crassipes in Conjunction

with Bacterial strains

PLANT MATERIAL


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To evaluate the effects of bacterial strains in conjunction with Pistia stratiotes and Eichhornia

crassipes three different pHs were selected (5, 7 and 9) for the removal of chromium at initial

concentration of 300g ml-1 from aqueous solutions with no nutritional ingredients added to the

test. Four sets were prepared for each strain which were control, bacterial test, plant test and

plant/bacterial test. Bacterial inoculum of 100g ml-1 was added in the solution. The incubation was

done at room temperature for 48 hours.

BACTERIAL STRAINS

Four chromium-resistant bacterial strains, CrS2, CrS3, CrS4 and CrS6 isolated from chromium

contaminated water and soil, were used in this study. The bacterial strains were maintained on

nutrient agar medium supplemented with 1000g ml-1 of K2CrO4.

CHROMIUM REDUCTION ASSAY

After 48 hours of exposure to Cr (VI), plants were harvested and washed with autoclaved distilled

water twice to remove the loosely bound or attached chromium to the roots and aerial parts.

Harvested plants were oven dried at 800C for 24 hours. The amount Cr (VI) left in the solution was

then determined by using the classical spectrophotometric method.

Results

Water samples (A, B, C) from the effluents of Itehad Chemicals, East Pak tannery and chromatic

disposal of Pak-Arab Fertilizer were collected. The strain isolated was: CrS3. Soil samples (D, E, F,

G, and H) from various chromium polluted areas including East Pak tannery, Itehad Chemical

Industry and Pak-Arab Fertilizer Plant were collected. The strains isolated from polluted soil were:

CrS2, CrS4 and CrS6.

Colony morphology. Majority of the strains (CrS2, CrS4 and CrS6) showed off-white color,

whereas strain CrS3 showed orange/brown pigment. All strains had circular colonies except CrS4


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which had eye-shaped colonies. Convex elevation was seen in all strains except CrS3 which had

raised elevation. The size of the colonies ranges from less than 1mm to 4mm. Strain CrS3 showed

butyrus consistency. Strain CrS6 showed viscid consistency while CrS2 showed viscid/moist

consistency (Table 1).

Cell morphology. Some of the strains were gram-negative: CrS2 (coccobacilli), CrS4 (bacilli).

While some strains were gram-positive: CrS3 cocci, CrS6 coccobacilli. Spore-staining under heavy

metal stress showed that strain CrS3 formed spores due to heavy metal stress of 2000g/ml

concentration. Whereas strains CrS2, CrS4 and CrS6 did not make any spores. Almost all the

strains CrS2, CrS4 and CrS6 had capsules around their cells except CrS3. All strains were found

out to be motile except CrS6 (Table 2).

Biochemical characterization. Every strain gave positive results for catalase and cytochrome

oxidase. All the strains were strict aerobes while strain CrS2 was facultative anaerobe. Only two

strains CrS3 and CrS6 were starch hydrolyzing. All the strains showed growth on MacConkeys

agar (Table 3).

Heavy metal resistance. To check the heavy metal resistance profile of chromium-resistant

bacteria, five heavy metals were used. All the strains managed to resist NaSe and MnSO4 to a

higher level. Strain CrS3 could not resist MnSO4 at a concentration of 2000g ml-1. None of the

strains could resist ZnSO4, CoCl2 and CuSO4 at a concentration of 500g ml-1. Only two strains

CrS2 and CrS4 resisted ZnSO4 up to 250g ml-1 concentrations. Only two strains CrS2 and CrS6

resisted CoCl2 up to 250g ml-1 concentrations. All the strains resisted CuSO4 up to 250g ml

-1

concentrations except strains CrS3 (Table 4).

Antibiotic sensitivity. Strains CrS2, CrS4 and CrS6 were resistant to Carbencillin, whereas strain

CrS3 was sensitive to it. All the strains were found out to be highly sensitive to Oxy-Tetracyclin.


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Strains CrS2 and CrS6 were resistant to Erythromycin, whereas strains CrS3 and CrS4 were

sensitive to this drug. Strains CrS2, CrS4 and CrS6 were resistant to Ampicillin whereas strain

CrS3 was sensitive to it. Strains CrS4 and CrS6 showed resistance toward Chloramphenicol. Strain

CrS3 was sensitive to it, whereas strain CrS2 was intermediate. All the strains were found out to be

resistant to Penicillin except strain CrS3. All the strains were found out to be resistant to

Novobiocin except strains CrS3 (Table 5).

Plasmid profile. By observing the gel under UV radiation lamp, bands of plasmid DNA were seen

in all the strains. There were multiple plasmids in the strains CrS2 and CrS6. A known size of

ladder 10kb was also run along with the unknown plasmids. The plasmids of strains CrS2, CrS3,

CrS4 and CrS6 were either of 10kb or larger, labeling them as mega-plasmids (Table 6).

Chromium reduction. The reduction potential of isolated strains was checked at three different

initial hexavalent chromium concentrations which were 100, 500 and 1000g ml-1. Soluble Cr (VI)

was reduced at all the treatments with all bacterial strains, however, reduction ability varied with

the strains. The maximum reduction was done by strain CrS6 at 100g ml-1. In general the

reduction of Cr (VI) to Cr (III) was lower at initial concentration (100g ml -1) but at higher initial

concentrations (500 and 1000 g ml-1) overall more chromium was reduced but percentage

reduction was less as compared with the lower concentration (Figure 1).

Effect of pH and temperature. Almost all the strains reduced more Cr (VI) at pH 9 at Cr (VI)

concentration of 100 and 500g ml-1. At Cr (VI) concentration of 1000 g ml-1, increased reduction

was again observed at pH 9 except the strain CrS2 (Figure 2). All the strains followed a wide range

of temperature for Cr (VI) reduction but the strains CrS4 and crS6 preferred high temperature of

450C (Figure 3).


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Effect of different heavy metals. All the strains show more reduction with NaSe at initial

concentration of 500g ml-1 of chromium. The highest Cr (VI) reduction recorded with NaSe was

67.95% by strain CrS6 at 500g ml-1. All the strains showed increased reduction with CoCl2 at

100g ml-1. Strain CrS6 showed more Cr (VI) reduction with MnSO4 at initial concentration of

100g ml-1 except strains CrS2, CrS3 and CrS4 which showed increased reduction at initial

concentration of 500g ml-1. With ZnSO4 highest Cr (VI) reduction was recorded at initial

concentration of 100g ml-1 (Figure 4-6).

Removal of chromium-Pistia stratiotes + bacteria. When bacteria and plants were used together

it was observed that reduction increased with their association. Most of the strains reduced

chromium efficiently at pH 5 and 9. At neutral pH chromium reduction was comparatively less

efficient.

Eichhornia crassipes + bacteria. After 48 hours, it was observed that plant removed less

chromium (2.8%). All the isolates reduced more chromium as compared with plant.

Discussion

Resistance against toxic Cr is more prominent among prokaryotes than the eukaryotes. Some gram-

positive bacteria have been reported to be able to detoxify Cr (VI) by reducing it to Cr (III) (Fuji et

al. 1990; Basu et al.1997). Industrial wastewater is often polluted by Cr (VI) compounds,

presenting a serious environmental problem (Vatsouria et al; 2005). Chromiums interaction with

biological systems is very different and complex (Vankar and Bajpai, 2007).

The treatment of heavy metal wastewater by using microorganism is one of the most active

research fields in recent years (Leusch et al., 1995; Kaewsarn, 2002; Wu et al., 1996). It is a well

known fact that aquatic plants accumulate metals that they take from the environment and


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concentrate on the trophic chains with accumulative effect (Outridge and Noller, 1991; Tremp and

Kohler, 1995).

The use of dead, dried aquatic plants, for water removal of metals derived from industrial activities

as a simple biosorbent material has been increasing in the last years. The mechanism of

simultaneous metal removal (Cd, Ni, Cu, Zn, Cr and Pb) by 3 macrophytes biomass (Spirodela

intermedia, Lemna minorand Pistia stratiotes) was investigated (Miretzky et al.2006).

The present study deals with the reduction of Cr (VI) by chromium-resistant bacterial strains in

conjunction with phytoextraction of Cr (VI) by hydrophytes. For this reason four chromium-

resistant bacterial strains and two Cr (VI) accumulating hydrophytes were isolated and selected. All

the strains showed resistance to chromium at initial concentration of 1000g ml -1 (Horton et al.

2006). In a study conducted by Amoozegaret al. (2007), the strains could tolerate up to 600mM of

chromate and completely reduced 0.2mM highly toxic and soluble Cr (VI) into almost non-toxic

and insoluble Cr (III) under aerobic condition. On the basis of morphological characterization

(table 1) it was found out that, strain CrS3 was affiliated with family Micrococcaceae. Similarly

Srinath et al. (2001) also isolated gram-positive chromium-resistant cocci demonstrating

physiological characteristics primarily indicative of genera Micrococcus. CrS6 was gram-positive

coccobacilli, CrS2 was gram-negative coccobacilli, and CrS4 was gram-negative rod and was

affiliated with family Pseudomonadaceae. According to Vitti and Giovannetti (2000), gram-

positive bacteria are more metal tolerant than gram-negative bacteria.

The isolated bacterial strains were able to resist chromium but each strain showed multiple

resistances towards various heavy metals which included ZnSO4, CoCl2, CuSO4, MnSO4 and NaSe

(Table 4). In a study Thacker et al. (2006), a gram-negative chromate reducing bacteria also


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exhibited multiple heavy metals (Ni, Zn, Hg, Pb, Co) tolerance. Abou-Shanab et al. (2007) showed

that chromium-resistant bacteria can also resist Mn.

Majority of the strains were resistant to Ampicillin, Chloramphenicol, Penicillin, Erythromycin,

Carbencillin and Novobiocin. The bacterial strains isolated by Faisal and Hasnain (2000) were also

resistant to Ampicillin and Chloramphenicol.

Gel electrophoresis revealed that all the strains contained plasmids (Table 6). All the strains

contained mega plasmids. Vitti et al. (2002) also isolated chromium-resistant bacteria that harbored

one and two plasmids of high molecular mass.

Although the strains can reduce Cr (VI) at wide range of pH (pH 5-pH 9) efficiently, its optimum

pH was recorded at pH 9 (Figure 2). Similarly, (Camargo et al. 2002), showed that maximum Cr

(VI) reduction was observed at the optimum pH (7-9). All the strains done reduction efficiently at a

wide range of temperature (280C-450C), the optimum was recorded to be 450C (Figure 3). In

another study, Wang et al. (1989) showed that chromate reduction was observed at a temperature

range of 10-400C.

All the strains showed increased reduction in the presence of heavy metals at all of the three initial

chromium concentrations better than when strains were growing only in chromium supplemented

medium (Figures 4-6). In one study, by Van Berkum et al. (2007), six strains were found out to be

resistant to Mn, Zn and Pb and displayed different degrees of chromate reduction (42-95%) under

aerobic conditions.

The overall removal of Cr by both the action of plant along with bacterial strains was more as

compared to the non-inoculated control. The effect of pH on the uptake of Cr (VI) by roots of

Pistia stratiotes showed that maximum uptake (20.54%) of chromium was done at pH 5 within 48

hours. Miretzky et al. (2004) showed that Pistiastratiotes remove more than 85% of chromium


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within 24 hours. Eichhornia crassipes did less reduction (2.8%) solitarily. Singhal and Rai (2003)

reported that Eichhornia crassipes could easily grow in the industrial effluents and can take up

metal and toxic materials for its metabolic use. Phytoextraction of chromium by Pistia stratiotes

from wastewaters in conjunction with chromium-resistant bacterial isolates proves to be very

promising technology which is cheap, effective and safe and can be installed on an industrial scale

without fear of environmental hazard.

Conclusion

By analyzing the results it can be concluded that isolates in the present study are very efficient in

reducing chromium. All the four strains can be considered as good candidates for application on an

industrial scale for removing toxic Cr (VI) because in polluted environment a lot of other metals

and antibiotics might also be present with the target metal and these bacterial strains showed

multiple resistances towards different heavy metals and antibiotics. Pistiastratiotes plants were

much more efficient in the removal of chromium from wastewater as compared with Eichhornia

crassipes. Phytoextraction of chromium by Pistiastratiotes from wastewaters in conjunction with

chromium-resistant bacterial isolates proves to be very promising technology which is cheap,

effective and safe and can be installed on an industrial scale without fear of environmental hazard.

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Table-1 Morphological Characteristics of Chromium-Resistant

Colony Morphology CrS2 CrS3 CrS4 CrS6

Size Punctiform Moderate Large Punctiform

Measurements Less than 1mm 2 mm 4 mm Less than 1 mm

Consistency Viscid/moist Butyrus Mucoid Viscid

Elevation Convex Raised Convex Convex

Pigmentation Off-white

Brown/orang

e Off-white Off-white

Form Circular Circular Eye-Shaped Circular


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Table-2 Cell Morphology of Chromium-Resistant Bacterial Strains

Strains

Morphological characteristics

Gram-staining Cell shape Spore-

formation

Capsule-

formation

Motility

CrS2 Gram-negative Coccobacilli - + +

CrS3 Gram-positive Cocci + - +

CrS4 Gram-negative Bacilli - + +

CrS6 Gram-positive Coccobacilli - + -


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Table-3 Biochemical Characteristics of Chromium-Resistant Bacteria

Characteristics CrS2 CrS3 CrS4 CrS6

Catalase + + + +

Cytochrome oxidase + + + +

Oxidation/Fermentation F.A A A AStarch hydrolysis - + - +

MacConkeys agar + NLF + NLF + NLF + NLF


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Table-4 Heavy Metal Resistance Profile of Chromium-Resistant Bacteria

Strains

Heavy Metals (g ml-1)

g ml-1 ZnSO4 NaSe MnSO4 CoCl2 CuSO4

CrS2

250 - + + + +500 - + + - -

2000 + +

CrS3

250 - + + - -

500 - + + - -

2000 + -

CrS4

250 + + + + +

500 - + + - +

2000 + +

CrS6

250 - + + - -

500 - + + - -2000 + -


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Table-5 Antibiotic Sensitivity Profile of Chromium-Resistant Bacteria

Antibiotics in

g/ml

Strains

CrS2 CrS3 CrS4 CrS6

Zone

diameter

S,R,I Zone

diameter

S,R,I Zone

diameter

S,R,I Zone

diameter

S,R,I

Carbencillin

CAR-100

0 mm R 37 mm S 0 mm R 0 mm R

Oxy-Tetracyclin

OT-30

32 mm S 23 mm S 30 mm S 35 mm S

Erythromycin

E-15

12 mm R 24 mm S 25 mm S 10 mm R

Ampicillin

Amp-25


Chloramphenicol

C-30

15 mm I 25 mm S 12 mm R 9 mm R

Penicillin

P-10


Novobiocin

NV-5


S= sensitive

R= resistant

I= intermediate


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Table-6 Plasmid Profile of Chromium-Resistant Bacteria

Strains

Plasmid Profile

Plasmids Presence No. of Plasmids Plasmid Size

CrS2 + 02

01 Larger than 10 kb


CrS3 + 01 10 kb

CrS4 + 01 10 kb

CrS6 + 02




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Legends of the figures

Figures Description

Fig 1 Chromium Reduction at Different Initial Cr (VI) Concentration

Fig 2 Effect of pH 9 at Different Initial Concentrations of Cr (VI)

Fig 3 Chromium Reduction at 450C at an Initial Cr (VI) concentration of 100g/ml,

500g/ml, 1000g/ml

Fig 4 Chromium Reduction by Bacterial Strains in the Presence of Different Heavy Metals

at Initial Cr (VI) Concentration of 100g/ml






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Chromium R educt ion at D i

Initial Cr (VI) Concentra

0

10

20

3040

50

CrS2 CrS3 CrS4 CrS6

Bacter ia l S tra

PercentageCr

(VI)Reduction 1 0 0 g / m

5 0 0 g / m

1000g/

Figure 1. Chromium Reduction at Different Initial Cr (VI) Concentration


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Effect of pH 9 at Different Initial

Concentrations of Cr (VI)

0

10

20

30

40

50

60

70

80

Cr S2 Cr S3 CrS 4 CrS 6

Bacterial Strains

PercentageCr(VI)

Reduction

pH 9 100g/ml

pH 9 500g/ml

pH 9 1000g/ml

Figure 2. Effect of pH 9 at Different Initial Concentrations of Cr (VI)


25/28

Chromium Reduction at 450C at a n Initi

Cr (VI) concentration of 100 g/m

500g/ml and 1000g /ml

0

10

20

30

40

50

CrS2 CrS3 CrS4 CrS6

Bacterial Strai

Percentag

eCr(VI)

Redduction 100g/ml

500g/ml

1000g/

Figure 3. Chromium Reduction at 450C at an Initial Cr (VI) concentration of 100g/ml,

500g/ml and1000g/ml


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Chromium Re duction by Ba cterial S

the Pres ence of D ifferent He avy M

Initial Cr (VI) Co ncentration o f 100

0

2 0

4 0

6 0

8 0

10 0

C rS2 C rS3 C rS4 C rS6

Bacterial s trai

PercentageC

r(VI)

Reductio

n

NaSe

Co Cl2M nSO

Zn SO4

Cu SO4

Figure 4. Chromium Reduction by Bacterial Strains in the Presence of Different Heavy

Metals at Initial Cr (VI) Concentration of 100g/ml


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Chromium Reduction by Bacterial S

the Prese nce of Dif ferent Hea vy M

Initial Cr (VI) Conce ntration of 50 0

0

20

4060

80

10 0

C rS 2 C rS 3 C rS 4 C rS 6

Bacterial Stra

PercentageC

r(VI)

Reduction

NaSe

CoCl2

M nSO

Z n S O 4

C u S O 4




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Chromium Reduction by Bacterial Stra

the Prese nce of Different Heavy M eta

Initial Cr (VI) Concentration of 1000

0

10

20

30

40

CrS2 CrS3 CrS4 CrS6

Bacterial Strai

PercentageCr(VI)

Reducti

on

NaSe

CoCl2

MnSO4

ZnSO4

CuSO4



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