Journal of Environmental Biotechnology
Vol. 9, No. 2, 123–129, 2009

Original paper (regular paper)

Characteristics of Arsenic Removal from Aqueous Solution by Bacillus
megaterium Strain UM-123
MUNETOSHI MIYATAKE * and SACHIO HAYASHI
Department of Applied Chemistry, University of Miyazaki, 1–1 Gakuen Kibanadai Nishi, Miyazaki 889–2192, Japan
TEL: +81–985–58–7316 FAX: +81–985–58–7323
E-mail: t0g205u@cc.miyazaki-u.ac.jp(Received; 15 July, 2009/Accepted; 5 October, 2009)
Arsenic removal using microorganisms is an interesting alternative to conventional methods. Bacillus megaterium strain
UM-123, isolated from soil in Miyazaki, has been characterized as a novel arsenic-removing bacterium. Strain UM-123 iscapable of removing arsenic from culture medium supplemented with As(III) or As(V). Arsenic of 0.386 mg As/g (dryweight) was removed by strain UM-123 when the strain was grown on medium containing 5.0 mg As/l As(III) for 24 hours.
In experiments of arsenic adsorption by dried cells of strain UM-123, As(V) was scarcely adsorbed by cells, while As(III) was
adsorbed. The adsorption equilibrium data for As(III) are well-described by the typical Langmuir adsorption isotherm. The
maximum adsorption capacity was estimated to be 0.127 mg As/g (dry weight). The ratio of As(III) adsorption by strain
UM-123 was 93% or more in arsenic solutions up to 1.0 mg As/l. Arsenic concentrations in solution decreased to 0.01 mg
As/l or less with initial concentrations of up to 0.2 mg As/l. These results suggest that strain UM-123 may be utilized forbioremediation of arsenic-contaminated water.
Key words: arsenic removal, arsenic adsorption, bioremediation, Bacillus megaterium strain UM-123

1. Introduction
Arsenic is widely distributed in the Earth’s crust. It is released as a result of natural phenomena such as volcanic
activity or weathering, and human activities such as extraction of fossil fuels and other resources, industrial production, or extensive use of underground water; thus, arsenic is
becoming an environmental pollutant3,14,18). Arsenic is extremely toxic to humans, and numerous cases of serious
health damage caused by arsenic have been reported worldwide in recent years. Environmental pollution by arsenic has
therefore become a grave social problem8,10). In countries
such as India and Bangladesh, where most of the drinking
water comes from underground sources, water contaminatedwith arsenic has seriously aﬀected the health of 57 million
people. Removing arsenic from underground water has
therefore become essential for ensuring the safety of drinking water, as well as for protecting aquatic environments9).
Water contaminated with arsenic is generally purified
using physico-chemical methods such as coagulation andcoprecipitation, ion exchange, or adsorption, but thesemethods are expensive and produce secondary pollutants20).
Furthermore, these methods are regarded as problematic asthey are unable to suﬃciently remove As(III) or low-concentration arsenic. The need for low-cost, environmentallyfriendly technologies for removing arsenic from water has
recently become all the more pressing, and there is now

great interest in the use of bioremediation in order tocounter contamination by arsenic and other metals, withvarious studies being carried out in this field2,15,19). There is
every possibility that microorganisms with the ability to remove environmental arsenic can be used for bioremediation,and there are hopes that this approach could replace or
supplement existing physico-chemical methods. Microorganisms that possess mechanisms for insolubilizing and reducing
the toxicity of various harmful metals have been reported,and adsorption techniques using microbial biomass arebeing investigated13,16).
Adsorption of metals by microorganisms is generally
believed to occur because metals carry a positive charge,
while the microbe surface carries a negative charge. Arsenic
is not usually adsorbed by microorganisms because in neutral
aqueous solutions such as underground water, As(V) is present as negatively charged oxide ions (H2AsO4−，HAsO42−)
and As(III) is present as a neutral oxide (H3AsO3)3). For arsenic to be adsorbed by microorganisms, the surface of the
microorganisms must be changed by some form of pre-processing, which may be either chemical, such as the use of
surfactants, or physical, such as in heat processing4,6). With
the exception of some marine bacteria and a few geneticallymodified E. coli that have been reported previously, no bacteria have yet been found that can be used for bioremediation of arsenic, and thus the use of microorganisms forarsenic removal has not to date yielded satisfactory

MIYATAKE and HAYASHI

124

results5,11,17).
The aim of the present study was to discover a bacteriumthat can remove arsenic from the environment and that canbe used for bioremediation without the need for pre-processing. Particular focus was placed on the eﬀectiveness ofthe bacterium in removing As(III), which is highly toxic andis generally diﬃcult to remove, and furthermore on suﬃcient ability to remove arsenic at low concentrations. We
found that a Bacillus megaterium strain UM-123 isolated
from soil in Miyazaki Prefecture was capable of removing
arsenic. We carried out a detailed investigation of the characteristics of the arsenic-removing capacity of this strain,
confirming the possibility that it could be used for bioremediation.

2. Materials and Methods
2.1. Sample strain
Bacillus megaterium strain UM-123 isolated from soil in
Miyazaki Prefecture was used for the experiments. This
bacterium was identified in NCIMB Japan Co., Ltd..
2.2. Experiments during bacterial culture
Nutrient broth (Nissui Pharmaceutical Co., Ltd., Japan)
was used as medium. Sodium arsenite (Wako Pure Chemical Industries, Ltd., Japan) was used as an arsenic As(III)source, and disodium hydrogenarsenate (Wako Pure Chemical Industries, Ltd., Japan) was used as an arsenic As(V)source. Preculture was prepared using nutrient broth alone
at 30°C for 24 hours, with agitation at 100 strokes/min.
Experimental cultures were prepared by 100 ml of culture
broth inoculating from the preculture at a proportion of
2.0% (v/v) into nutrient broth containing As(III) or As(V)at concentrations of 0.5-100.0 mg As/l, and culturing aerobically in 500-ml shake-flasks at 30°C for 48 hours withagitation at 100 strokes/min. The turbidity of the culture
broth was measured at fixed intervals, after which bacterial
cells were separated from the culture broth by centrifugation (10,000×g for 15 min), and the respective concentrations of As(III) and As(V) in the broth supernatant were
measured. Harvested cells were washed twice with distilledwater and then lyophilized, after which the weight wasmeasured. The amount of arsenic removed per gram of thedry weight of cells was calculated based on the decreasein arsenic in the broth supernatant and the weight of thelyophilized cells.
In order to determine the arsenic content of the cytosol,
lyophilized bacterial cells obtained from media containing
1.0 mg As/l were suspended in purified water, and suspended cells were disrupted by ultrasonication; cells thus disrupted were separated from the supernatant by centrifugation(10,000×g for 15 min), and the concentrations of As(III)and As(V) in the supernatant were measured. To determine
the arsenic content of the cell wall, disrupted cells obtained
by ultrasonication were washed and lyophilized, and were
subjected to alkaline degradation in a 2.0 mol/l aqueous

solution of NaOH at 100°C for 3 hours, after which thearsenic concentrations were measured. To determine theAs(III) and As(V) content of the cell wall, arsenic was solubilized from lyophilized cells, which were obtained by ultrasonication, with the cell-wall-lytic enzyme lysozyme fromchicken egg white (Wako Pure Chemical Industries, Ltd.,
Japan). The solution was filtered, and the concentrations of
As(III) and As(V) were then measured. The sugar content
of the cell wall was determined using the phenol-sulfuric
acid method on the solution obtained from alkaline degradation.
Oxidation-reduction reactions of arsenic were carried out
in culture broth prepared using nutrient broth alone at 30°C
with agitation at 100 strokes/min. The supernatant obtained
from centrifuged culture broth as an extracellular solution,and the supernatant obtained following ultrasonication as
an intracellular solution were used respectively to determine
the extracellular activity and intracellular activity. As(III) or
As(V) solutions regulated to pH 7 were added to each supernatant to give final arsenic concentrations of 1.0 mg As/l,and were incubated at 30°C for 2 hours. The concentrationsof As(III) and As(V) were then measured.
2.3. Experiments using dried cells
Bacterial cells obtained from a culture in nutrient brothalone at 30°C for 24 hours with agitation at 100 strokes/
min were harvested by centrifugation (10,000×g for 15 min)and lyophilized. Lyophilized bacterial cells were used for
dried cells.
The eﬀects of pH were investigated by adding 20 g dw/l
dried cells to 1.0 mg As/l solutions of As(III) or As(V) regulated at pH 2-12, and the suspensions were stirred at 30°C.
At fixed intervals, cells were removed by centrifugation(10,000×g, 15 min) and the concentrations of As(III) andAs(V) in the resulting supernatant were measured.
In order to investigate the eﬀects of temperature, 20 g
dw/l dried cells were added to 1.0 mg As/l solutions of
As(III) regulated at pH 7 at temperatures of 30-60°C, andwere stirred for 4 hours. Concentrations of As(III) andAs(V) in the supernatant were then measured.
The eﬀects of arsenic concentration were investigated byadding 20 g dw/l dried cells to solutions of As(III) of 0.0210.0 mg As/l regulated at pH 7, and these suspensions werestirred at 35°C for 4 hours. Concentrations of As(III) andAs(V) in the supernatant were then measured. The amountof arsenic adsorption was calculated based on the decreasein arsenic in the supernatant and the weight of dried cells
added in solution. The equilibrium concentration of arsenic
and the amount of arsenic adsorption thus determined were
substituted into the Langmuir isotherm given below to determine the maximum adsorption.
Langmuir isotherm: Ceq/q = 1/qmaxK+Ceq/qmax
where, q is arsenic adsorption (mg As/g dw), Ceq is the equilibrium concentration of arsenic (mg As/l), qmax is the maximum adsorption (mg As/g dw), and K is the equilibrium
constant (l/mg As).

Arsenic removal by B. megaterium

125

2.4. Analysis
The turbidity of the culture broth was measured using aspectrophotometer UV-210A (Shimadzu Co., Japan) at
600 nm, and the values were used as indicators of the levelof bacterial growth. Quantitative analysis of arsenic wascarried out using an atomic absorption spectrophotometerAA 6650 with an arsenic speciation pretreatment system
ASA-2sp (Shimadzu Co., Japan) in order to determine theconcentrations of As(III) and As(V). All experiments werecarried out three times, and measurements were performed
twice. All of the obtained values were in the range of ±3%
from average values. All results are given as average values.

3. Results
3.1. Effects of arsenic on bacterial growth and the
behavior of arsenic during culture
Changes over time in the broth turbidity at concentrations of 10.0, 50.0, and 100.0 mg As/l As(III) and As(V),when Bacillus megaterium strain UM-123 was cultured in
medium containing arsenic, are shown in Fig. 1. In bacterial
growth at each arsenic concentration, almost no diﬀerenceswere observed between the logarithmic growth phase ofbacteria in culture with either As(III) or As(V) at concentrations of 10.0 mg As/l and culture to which no arsenic had
been added, and growth reached the stationary phase in
12 hours. At a concentration of 50.0 mg As/l or more, therate of bacterial growth was slower than in concentrationsof 10.0 mg As/l, and it took 24 hours or more to reach astationary phase. With As(V), at a concentration of
100.0 mg As/l, bacterial growth stopped after 6 hours,
reaching a stationary phase, and turbidity during the stationary phase was approximately 20% of the stationary
phase turbidity at concentrations of up to 50.0 mg As/l.
These results indicate that As(V) inhibits the growth ofstrain UM-123 more than As(III).
Changes over time in the arsenic remaining in culture
medium at concentrations of 0.5-100.0 mg As/l As(III) andAs(V), when strain UM-123 was cultured in medium containing arsenic, are shown in Fig. 2. Fluctuations were observedin the changes in arsenic concentrations in the culture medium over time for each culture up to 10.0 mg As/l As(III)and 5.0 mg As/l As(V). At these concentrations, the ratioof arsenic remaining in the culture medium reached thelowest values at 24 hours of culture time, after which they
increased. In the ratios of arsenic remaining in the culture
medium at 24 hours, this value was lower for lower concentrations of arsenic added to media. When 0.5 mg As/l wasadded, the remaining arsenic was 45.3% of the initial concentration for As(III) and 55.2% for As(V); the ratio of
As(III) remaining was thus lower than that for As(V) at thesame initial concentration. The amount of arsenic removed
per gram of dry weight of cells was 0.386 mg As/g dw for
As(III) and 0.311 mg As/g dw for As(V), at a concentrationof 5.0 mg As/l.

Fig. 1. Effect of arsenic concentration on cell growth of strain UM123.

With regard to the species of arsenic remaining in theculture medium over the culture time, when As(III) was
added to the media, the proportion of As(V) at the start ofthe culture remained largely unchanged up until 24 hours ofculture time, after which it rose somewhat. On the other
hand, when As(V) was added, the proportion of As(V) inthe culture medium showed a rapid decrease from the startof the culture until 24 hours of culture time, after which itrose somewhat, as was the case when As(III) was added.
The same changes were observed with As(III) and As(V) up
to concentrations of 50.0 mg As/l; at 50.0 mg As/l As(V),the total concentrations of arsenic did not vary over time,and only the species of arsenic changed. At As(III) andAs(V) concentrations of 100.0 mg As/l, no changes overtime were observed in either the total arsenic concentrations
or in the species of arsenic in the culture medium.
The distribution of arsenic removed from culture medium
by strain UM-123 is shown in Table 1. Regardless of whether
the arsenic added to the medium was As(III) or As(V), withthe exception of a culture time of 6 hours, 90% or more of
the arsenic removed from the culture medium was present
in the cell wall, and was all As(III). Conversely, the arsenic
present in the cytosol was 68-76% As(III). The amount ofsugar per gram of cell wall for each culture time reached its
highest value after 24 hours of culture and subsequently
decreased, exhibiting the same behavior as the amount ofarsenic removed from the culture medium.
3.2. Oxidation-Reduction of Arsenic by strain UM-123
Intracellular and extracellular solutions from three diﬀerent culture times were used to investigate arsenic oxidationreduction activity, and the results are shown in Table 2.
When As(III) was added to the intracellular solutions, theproportion of As(V) increased from 10% to around 28%,
irrespective of the culture time, indicating that oxidation of
As(III) to As(V) did occur. When As(III) was added to the126

MIYATAKE and HAYASHI

Fig. 2. Time courses of arsenic removal by strain UM-123 grown with 0.5 mg As/l and 1.0 mg As/l As(III) (A), 5.0 mg As/l and 10.0 mg As/lAs(III) (B), 50.0 mg As/l and 100.0 mg As/l As(III) (C), 0.5 mg As/l and 1.0 mg As/l As(V) (D), 5.0 mg As/l and 10.0 mg As/l As(V)(E), and 50.0 mg As/l and 100.0 mg As/l As(V) (F).
Remaining arsenic in the culture broth was calculated by considering the initial arsenic concentration to be 100%.

extracellular solution, the proportion of As(V) increased
to 52.2%, indicating that oxidation of As(III) to As(V)occurred, but only when the extracellular solution from aculture time of 48 hours was used. When As(V) was added to the intracellular solutions, the proportion of As(III)increased from 13% to around 78%, irrespective of theculture time, indicating that the reduction of As(V) to As(III)occurred. When As(V) was added to the extracellular solutions, no changes were observed.

3.3. Removal of Arsenic from Aqueous Solution Using
Dried Cells
The changes in the adsorption ratios over time at diﬀerent pH levels were investigated. The arsenic adsorption
behavior diﬀered according to pH, but under all pH conditions the maximum adsorption ratio was observed at
4 hours of contact time. In addition, in the As(III) solution,arsenic remained as As(III), with no change to As(V) observed under any of the pH conditions. Arsenic adsorption
at 4 hours of contact time for each pH condition is shownin Fig. 3. Adsorption was 87.4% at pH 7, and at near-neutral

Arsenic removal by B. megaterium

127

Table 1. Distribution of arsenic removed by strain UM-123 and sugar in cell wall of strain UM-123.
Cytosol
Culture Cell amount As(III)time (h) (g dw/l broth) (μg As/
g dw)
As(III) addition
6
2.34
12
2.59
24
2.60
36
2.58
48
2.56
As(V) addition
6
2.34
12
2.58
24
2.60
36
2.53
48
2.56

As(V)
(μg As/g dw)

Cell wall

Total As
(μg As/(%)bg dw)

As(III)(μg As/
g dw)

As(V)
(μg As/g dw)

As removal
Sugar
(μg
As/g dw)(mg As/g dw)

Total Asa
(μg As/
(%)b
g dw)

5.4
2.7
2.8
2.0
1.9

2.5
1.2
1.2
0.9
0.8

7.9
3.8
4.1
2.8
2.7

12.9
3.7
2.4
2.5
6.3

50.6
96.3
162.4
108.9
38.9

—
—
—
—
—

50.6
96.3
162.4
108.9
38.9

83.1
93.3
96.1
97.0
90.9

2.64
13.83
28.73
20.31
9.84

60.9
103.2
169.0
112.3
42.8

0.2
3.2
3.4
2.0
1.8

0.1
1.0
1.1
0.6
0.6

0.3
4.2
4.5
2.6
2.5

15.9
5.7
3.4
2.8
6.5

1.6
67.5
124.7
89.4
34.2

—
—
—
—
—

1.6
67.5
124.7
89.4
34.2

81.1
91.3
95.1
96.5
90.0

0.09
9.92
22.29
16.76
8.72

2.0
74.0
131.2
92.7
38.0

Experimental methods are described in the text.
a
The values measured by the method of enzyme digestion are indicated as for the amounts of total arsenic in the cell wall, and are almost
the same as the values measured by the method of alkaline degradation.
b
Percentages of total arsenic in the cytosol and cell wall were calculated by considering total arsenic removed to be 100%.

Table 2. As(V) reduction and As(III) oxidization by strain UM-123.
As(V) ratio after
As(III) addition(%)a

Culture time (h)conrold
1224
48

As(V) ratio after
As(III) addition(%)a

ISb

ESc

IS

ES

9.8
28.4
27.2
27.9

9.7
10.8
11.4
52.2

13.3
78.6
78.3
77.8

13.2
13.4
13.2
12.9

Conditions of enzyme reactions: initial arsenic concentration, 1.0 mg As/l As(III) and As(V); pH, 7; temperature,
35℃ ; reaction time, 2 h.
aAs(III) and As(V) ratios in the reaction solution were calculated by considering the initial total arsenic concentration to be 100%.
b
Intracellular solution.
cExtracellular solution.
dControl experiment with purified water.

pH (pH 6, 7, 8) it was over 70%. Under acidic conditions(pH 2-5), arsenic adsorption was around 57%; under alkaline conditions, adsorption dropped sharply above pH 9
and was less than 5% at pH 12.
Arsenic adsorption under diﬀerent temperature conditions
is shown in Fig. 4. Adsorption was over 85% at temperatures of 30-45°C, but fell at temperatures above 50°C, andwas only 20.0% at 60°C. Maximum adsorption was 93.2%
at 35°C.
The eﬀects of arsenic concentrations on arsenic adsorption were investigated, and the results are shown in Fig. 5.
Adsorption of 93% or more was observed up to a concentration of 1.0 mg As/l, and up to a concentration of 0.2 mg
As/l, the concentrations of arsenic in the solution decreased
to less than 0.01 mg As/l. The relationship between theequilibrium concentration and the amount of arsenic adsorption is shown in Fig. 6. The amount of arsenic adsorbed

increased exponentially with the concentrations of arsenic
added, and the equilibrium data closely match the Langmuir isotherm. The maximum adsorption amount determined in this way was 0.134 mg As/g dw.

4. Discussion
As(V) reduction can be achieved by various bacteria
possessing cytoplasmic As(V) reductase (ArsC), which ispart of an arsenic resistance system, and dissimilatory
As(V)-reducing bacteria (DAsRBs), which can grow by the
respiratory As(V) reduction under anoxic condition1,7,11).
ArsC is located internally within the cytoplasm in contrast
to the dissimilatory As(V) reductase of DAsRBs that is
located on the cell periphery. It is clear that ArsC diﬀer
both functionally and structurally from dissimilatory As(V)reductase. DAsRB Bacillus sp. SF-1 could not reduce As(V)128

MIYATAKE and HAYASHI

Fig. 3. Effects of pH on As(III) adsorption by dried cells of strain
UM-123.
Conditions of As(III) adsorption experiments: initial As(III)concentration, 1.0 mg As/l; dried cells, 20 g dw/l; temperature,
30°C; contact time, 4 h. As(III) adsorption was calculated as aratio of the adsorbed As(III) concentration against the initial
As(III) concentration.

Fig. 4. Effects of temperature on As(III) adsorption by dried cellsof strain UM-123.
Conditions of As(III) adsorption experiments: initial As(III)concentration, 1.0 mg As/l; dried cells, 20 g dw/l; pH, 7; contact time, 4 h. As(III) adsorption was calculated as a ratio of
the adsorbed As(III) concentration against the initial As(III)concentration.

under strictly aerobic conditions due to the presence of oxygen, which inhibited the As(V) reduction21). On the other
hand, strain UM-123 could reduce As(V) under strictly aerobic conditions. It was presumed that As(V) reduction bystrain UM-123 was carried out by ArsC of an arsenic resistance system. In the arsenic resistance system, As(V) entering the cell via phosphate transporters is reduced to As(III)by ArsC in the cytoplasm, and then is expelled from thecell via As(III)-specific transporters. Because this process
occurred in strain UM-123 similarly, the amount of As(III)Fig. 5. Effects of arsenic concentrations on As(III) adsorption by
dried cells of strain UM-123.
Conditions of As(III) adsorption experiments: dried cells, 20 g
dw/l; pH, 7; temperature, 35℃ ; contact time, 4 h. As(III) adsorption was calculated as a ratio of the adsorbed As(III) concentration against the initial As(III) concentration.

Fig. 6. Application of the equilibrium Langmuir model to As(III)adsorption on dried cells of strain UM-123.
Conditions of the As(III) adsorption experiments: dried cells,
20 g dw/l; pH, 7; temperature, 35°C; contact time, 4 h. Line
showed theoretical Langmuir curve.

in the culture medium, when As(V) was added to the medium,increased as the culture progressed.
As over 90% of the arsenic removed from the culture
medium was found to be present in the cell wall as As(III),
it is clear that strain UM-123 specifically adsorbs As(III) at
the cell wall. Furthermore, as changes in the amount ofarsenic removed from the culture medium per unit dry
weight exhibited the same behavior as the changes in cellwall sugar content, it may be conjectured that sugar in thecell wall is closely involved with the adsorption of As(III). It
may be further conjectured that the increase in arsenic concentrations in the culture medium from 24 hours of culture
time onward was because the sugar in the cell wall either
separated from the cell wall or was broken down as theculture progressed, so that the arsenic that had been adsorbed

Arsenic removal by B. megaterium

was subsequently desorbed from the cell wall. Whenlyophilized bacterial cells were used, As(III) alone wasspecifically removed from the aqueous solution. It would
therefore appear that the sequence of events resulting in
As(V) removal by bacteria in cultures medium did not occur
with dried cells; as lyophilized cells were unable to reduce
As(V) to As(III), they were unable to remove As(V). The
amount of sugar present per unit dry weight in the cell wall
immediately after lyophilization was 97% of the amountduring culture, while in the dried cells after the arsenic adsorption experiments it had decreased to 72% of the amountduring culture. The amount of arsenic removed was also
lower when dried cells rather than cultures were used, and it
would appear likely that in the adsorption experiments
using dried cells, the sugar in the cell wall either separated
from the cell wall or was broken down.
Among the bacteria that have been reported to date, themarine bacterium Marinomonas communis removes thegreatest quantity of arsenic, removing 2.290 mg As/g dw
from cultures containing 5.0 mg As/l As(V)17). However, theratio of arsenic removed is only 14.8% under these conditions, and is even lower in medium containing 0.07 mg As/lAs(V). The amount of As(III) adsorbed when M. communis
cells are used is 0.119 mg As/g dw, which is on the sameorder as that with strain UM-123. Moreover, even genetically modified E. coli bacteria, in which gene manipulation
techniques can result in a high expression of ArsR, the protein regulating the ars operon, or can induce production of
Arabidopsis thaliana phytochelatin, the amount of arsenic
removed is 0.110-0.173 mg As/g dw, which is on the sameorder as that with strain UM-1235, 11). Strain UM-123, inseveral bacteria without pre-processing, is the first bacterium
reported that possesses the same arsenic-removing capacity
as marine bacteria and genetically modified E. coli. Strain
UM-123 was able to remove both As(III) and As(V) fromthe culture medium during culture, and the ratio removed
was in the region of 55% in culture medium containing
0.5 mg As/l As(III). When dried cells were used, strain UM123 was only able to remove As(III). But by increasing thecell density to greater than when the strain was cultured, it
was possible to achieve an arsenic adsorption ratio of 93%
or more in solutions of As(III) of up to 1.0 mg As/l. Strain
UM-123 was also able to reduce the concentrations of arsenic in solutions up to 0.2 mg As/l to 0.01 mg As/l or less,which is the environmental standard for arsenic.
Based on the present results, it appears that strain UM123 is eﬀective in removing As(III), which is highly toxic
and diﬃcult to remove. Furthermore, this activity is maintained even at low concentrations of arsenic. UM-123 thus
appears to have suﬃcient potential for use in bioremediation.

129

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