J.Natn.Sci.Foundation Sri Lanka 2017 45 (3): 247 - 253 DOI: http://dx.doi.org/10.4038/jnsfsr.v45i3.8189
RESEARCH ARTICLE
Phenol degradation by Acinetobacter sp. in the presence of heavy metals S.A. Ahmad1*, N.A. Shamaan2, M.A. Syed1, F.A. Dahalan3, K. Abdul Khalil4, N.A. Ab Rahman1 and M.Y. Shukor1 1
Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, Selangor, Malaysia. Faculty of Medicine and Health Sciences, Universiti Sains Islam Malaysia, Kuala Lumpur, Malaysia. 3 The School of Environmental Engineering, Universiti Malaysia Perlis, Perlis, Malaysia. 4 Biomolecular Science Program, School of Biology, Faculty of Applied Sciences, Universiti Teknologi MARA, Selangor, Malaysia.
2
Revised: 30 September 2016; Accepted: 17 November 2016
Abstract: 7KH SXUSRVH RI WKLV VWXG\ ZDV WR LQYHVWLJDWH WKH ability of AcinetobacterVSVWUDLQ$412/LPPRELOLVHGLQ gellan gum beads to degrade phenol in the presence of heavy metals. Seven different heavy metals, namely, As5+, Cu2+, Cd2+, Ni2+, Cr6+, Pb2+, and Hg2+DWSSPZHUHWHVWHG5HVXOWVRIWKH VWXG\ VKRZHG WKDW GHJUDGDWLRQ RI SKHQRO E\ IUHH FHOOV ZDV inhibited by Hg2+, Cu2+ and Cr6+ after 48 hours of incubation by 97.91 %, 77.58 % and 75.26 %, respectively. Only Hg2+ and Cr6+ inhibited phenol degradation by immobilised Acinetobacter cells in 18 hours by 67.55 % and 53.19 %. Phenol GHJUDGDWLRQE\LPPRELOLVHGFHOOVZDVDIIHFWHGZKHQ&U6+ and Hg2+ concentrations exceeded 0.5 and 0.1 ppm, respectively. +RZHYHULQKLELWRU\HIIHFWVRIKHDY\PHWDOVFDQEHRYHUFRPHE\ prolonging the incubation time for immobilised Acinetobacter VS VWUDLQ$412/ IURP KRXUV WR DQG KRXUV IRU Cr6+ (46.80 %) and Hg2+ (21.40 %), respectively.
(Suhaila et al., 2013; Ahmad et al., 2014; Chander et al., $]ULet al., 2015). In a previous study (Ahmad et al., 2011; 2012), it ZDV UHSRUWHG WKDW Acinetobacter sp. VWUDLQ $412/ XWLOLVHGSKHQRODVWKHVROHFDUERQVRXUFHZLWKRSWLPXP WHPSHUDWXUHV UDQJLQJ EHWZHHQ WR & ,W KDV WKH ability to degrade 100 % phenol up to 1100 mg/L and 1900 mg/L by free and immobilised cells, respectively in 10 days. As both heavy metals and phenol are harmful SROOXWDQWVDQGRIWHQRFFXUWRJHWKHUWKLVVWXG\ZDVFDUULHG out to determine the effects of selected heavy metals on phenol degradation by the bacterium Acinetobacter sp.. 7KLV LQYHVWLJDWLRQ ZRXOG EH VLJQL¿FDQW LQ GHVLJQLQJ effective bioremediation strategies.
Keywords: Acinetobacter sp., biodegradation, heavy metals, immobilised cells.
METHODOLOGY
INTRODUCTION
Chemicals
Heavy metals can be toxic to microorganisms even at ORZ FRQFHQWUDWLRQV EXW VHYHUDO PLFURRUJDQLVPV KDYH EHHQVKRZQWRKDYHDQH[FHSWLRQDODELOLW\WRDGDSWDQG colonise noxious metal-polluted environments (Yusuf et al., 2016). Certain bacteria have developed capabilities to protect themselves from heavy metal toxicity by various mechanisms (Shukor et al., 2010; Halmi et al .DUDPED et al., 2015). Bioremediation is effective in degrading pollutants and thus able to get rid RI XQZDQWHG VXEVWDQFHV IURP LQGXVWULDO ZDVWHV VXFK DV phenolic compounds, dye, crude oil and hydrocarbons
$OOFKHPLFDOVXVHGZHUHRIDQDO\WLFDOJUDGHDQGSXUFKDVHG HLWKHUIURP0HUFN *HUPDQ\ RU6LJPD 86$
*
Corresponding author (
[email protected])
Microorganism and culture condition The phenol-degrading Acinetobacter sp. strain $412/XVHGLQWKLVVWXG\ZDVLVRODWHGLQ0DOD\VLD by Ahmad et al. (2011) as previously described. The EDFWHULXPZDVFXOWXUHGLQPLQHUDOVDOWPHGLXP 060 FRQWDLQLQJ J/ .2HPO4 .+2PO4, 0.2; NaCl, 0.1; MgSO4, 0.1; MnSO4.H2O, 0.01; Fe2(SO4).H2O, 0.01;
248
S.A. Ahmad et al.
NaMoO4.2H2O, 0.01; (NH4)2SO4, 0.4 at pH 7.5. The 060ZDVVXSSOHPHQWHGZLWKJ/ phenol as the sole carbon source.
degradation of phenol by free and immobilised cells occurred after 48 and 18 hours of incubation, respectively, ZKLOH JHOODQ JXP EHDGV ZLWKRXW FHOOV VKRZHG QR phenol degradation. *HOODQJXPJHOZDVVHOHFWHGDVWKH immobilisation matrix based on its established superior characteristics compared to carrageenan, agar, and alginate (Sanderson et al 1DZDZL et al., 2015; Yusuf et al., 2015).
Immobilised cells ,Q WKLV VWXG\ JHOODQ JXP JHO ZDV VHOHFWHG DV WKH FHOO LPPRELOLVDWLRQ PDWUL[ IROORZLQJ WKH PHWKRG GHVFULEHG by Ahmad et al. (2012). A combination of 7.5 % of JHOODQ JXP FRQFHQWUDWLRQ EHDG VL]H RI PP GLDPHWHU DQGEHDGQXPEHURISHUP/PHGLXPZDVXVHG as the entrapment matrix. In this study, degradation of 0.5 g/L phenol by free and immobilised cells (3.5 g/L of EDFWHULD ZDVWHVWHG*HOODQJXPEHDGVZLWKRXWEDFWHULD LQ 060 PHGLXP ZLWK SKHQRO ZDV XVHG DV WKH FRQWURO 3KHQRO GHJUDGDWLRQ ZDV PRQLWRUHG E\ FRORXULPHWULF assay for phenol using 4-aminoantipyrene as the reagent (APHA, 1998).
Heavy metals affect phenol degradation by impeding EDFWHULDO JURZWK DQGRU LQKLELWLQJ HQ]\PHV WKDW SOD\ major roles in phenol degradation (Nair et al., 2008; Arif et al 1RUD]DK et al., 2015). Heavy metals directly affect the membrane structure by disturbing the electron transport chain (Hall, 2002; Russak et al., 2008). Freely-suspended cells are exposed directly to the heavy PHWDOV DQG HDVLO\ UHDFW WKXV VORZLQJ GRZQ WKH UDWH RI degradation by disturbing the membrane structure. The effect of different heavy metals (1 ppm) on phenol biodegradation by freely-suspended and immobilised AcinetobacterVSVWUDLQ$412/LVJLYHQLQ7DEOH The results revealed that Cr6+, Cd2+, and Hg2+ inhibited SKHQROGHJUDGLQJDFWLYLW\E\LQKLELWLQJEDFWHULDOJURZWK at 5.5, 5.3 and 0.0 Log 10(CFU), respectively compared to the control 8.2 Log 10 &)8 S +RZHYHUWKLV VWUDLQKDVEHHQVKRZQWRKDYHDQH[FHSWLRQDODELOLW\WR adapt and protect itself from Cu2+, As5+, Ni2+, and Pb2+ S! 1DZDZLet al., 2015). Hg2+ gave the highest LQKLELWLRQRQSKHQROGHJUDGDWLRQZLWKRQO\ SKHQRO GHJUDGHGDIWHUKRXUVIROORZHGE\&G2+ (24.74 %) and Cr6+ (22.42 %). +RZHYHU ZLWK LPPRELOLVHG FHOOV RQO\ Hg2+ and Cr2+ inhibited phenol-degrading activities S XS WR DQG SKHQRO EHLQJ
The effects of heavy metals The effect of heavy metals on phenol degradation by the bacterium Acinetobacter VS VWUDLQ$412/ ZDV determined using both free and immobilised cells. In WKLV H[SHULPHQW 060 FRQWDLQLQJ J/ SKHQRO ZDV VHSDUDWHO\VXSSOLHGZLWKGLIIHUHQWKHDY\PHWDOV>DUVHQLF (As5+), chromium (Cr2+), cadmium (Cd2+), cuprum (Cu2+), nickel (Ni2+), lead (Pb2+), and mercury (Hg2+)] each at 1 ppm concentration. Bacterial cultures in free DQG LPPRELOLVHG FHOOV J/ ZHUH LQFXEDWHG LQ D rotary shaker at room temperature at 150 rpm. Based on this study (Figure 1), degradation of 0.5 g/L phenol ZDVDQDO\VHGDIWHULQFXEDWLRQIRUKUVIRULPPRELOLVHG cells and 48 hrs for free cells, because these are the optimal incubation periods for 100 % removal of phenol. 6LPXOWDQHRXVO\SKHQROGHJUDGDWLRQDQGEDFWHULDOJURZWK ZHUH YHUL¿HG XVLQJ DPLQRDQWLS\UHQH DQG FRORQ\ forming units methods, respectively.
ŽŶĐĞŶƚƌĂƚŝŽŶŽĨƉŚĞŶŽů;Őͬ>Ϳ
Ϭ͘ϱ
Statistical analysis $OOH[SHULPHQWVZHUHFDUULHGRXWLQWULSOLFDWHV7KHGDWD VKRZQLQWKHFRUUHVSRQGLQJ¿JXUHVDUHWKHPHDQYDOXHV of the experiment and expressed as mean ± standard deviation (STDEV).
September 2017
Ϭ͘ϯ Ϭ͘Ϯ Ϭ͘ϭ Ϭ͘Ϭ
Ϭ
ϲ
ϭϮ
ϭϴ
Ϯϰ
ϯϬ
ϯϲ
ϰϮ
ϰϴ
Incubation time (hours) /ŶĐƵďĂƚŝŽŶƚŵĞ;ŚŽƵƌƐͿ
RESULTS AND DISCUSSION Cell immobilisation is a promising approach in phenol biodegradation compared to free cells. In this study, immobilised Acinetobacter VS VWUDLQ $412/ LQ JHOODQ JXP EHDGV VKRZHG IDVWHU SKHQRO GHJUDGDWLRQ than free cells at 0.5 g/L of phenol (Figure 1). Complete
Ϭ͘ϰ
&ƌĞĞĞůůƐ
'ĞůůĂŶŐƵŵďĞĂĚƐ
ŽŶƚƌŽů
1 2
Figure 1: 'HJUDGDWLRQ RI SKHQRO DW J/ E\ IUHH Ɣ DQG LPPRELOLVHG Ŷ Acinetobacter VS VWUDLQ $412/ Ɣ Ŷ *HOODQ JXP EHDGV ZLWKRXW WKH SUHVHQFH RI EDFWHULD ZHUH Ÿ XVHGDVFRQWURO Ÿ
Journal of the National Science Foundation of Sri Lanka 45(3)
Journal of the National Science Foundation of Sri Lanka 45(3) 27.78 ± 0.00 100.00 ± 0.07
27.78 ± 0.00
100.00 ± 0.04
99.80 ± 0.05
27.72 ± 0.00
499.00 ± 0.00
95.60 ± 0.26
9.96 ± 0.00
478.00 ± 0.00
9.9 ± 0.51
12.40 ± 5.0
3.44 ± 0.00
62.00 ± 0.02
8.1 ± 0.09
Cu2+
1RWH 3KHQROPHGLDZLWKRXWWKHSUHVHQFHRIKHDY\PHWDOVZHUHXVHGDVFRQWURO Phenol degradation expressed as a percentage of 0.5 g phenol
500.00 ± 0.00
500.00 ± 0.00
95.60 ± 0.71
99.80 ± 0.06
9.96 ± 0.00
10.40 ± 0.00
478.00 ± 0.00
5.20 ± 0.55
9.40 ± 5.11
499.00 ± 0.00
1.44 ± 0.00
2.61 ± 0.00
9.8 ± 0.66
26.00 ± 0.01
47.00 ± 0.02
10.0 ± 0.51
8.1 ± 0.04
As5+
8.2 ± 0.15
Control
99.80 ± 0.09
27.72 ± 0.00
499.00 ± 0.00
24.80 ± 5.74
2.58 ± 0.00
124.00 ± 0.00
4.2 ± 0.08
6.00 ± 2.08
1.67 ± 0.00
30.00 ± 0.01
5.3 ± 0.28
Cd2+
99.80 ± 0.03
27.72 ± 0.00
499.00 ± 0.00
95.60 ± 0.88
9.96 ± 0.00
478.00 ± 0.00
10.0 ± 0.44
14.20 ± 8.33
3.94 ± 0.00
71.00 ± 0.03
8.1 ± 0.13
+HDY\PHWDOV SSP Ni2+
46.80 ± 4.84
13.00 ± 0.00
234.00 ± 0.02
22.40 ± 4.74
2.33 ± 0.00
112.00 ± 0.02
3.3 ± 0.12
6.40 ± 8.19
1.78 ± 0.00
32.00 ± 0.03
5.5 ± 0.18
Cr6+
99.80 ± 0.11
27.72 ± 0.00
499.00 ± 0.00
93.60 ± 0.86
9.75 ± 0.00
468.00 ± 0.00
10.0 ± 0.59
7.80 ± 1.80
2.17 ± 0.00
39.00 ± 0.04
8.2 ± 0.10
Pb2+
32.40 ± 3.58
9.00 ± 0.00
162.00 ± 0.02
2.00 ± 1.73
0.21 ± 0.00
10.00 ± 0.02
0.0 ± 0.00
0.60 ± 0.22
0.17 ± 0.00
3.00 ± 0.00
0.0 ± 0.00
Hg2+
degraded, respectively after 18 hours. Immobilised cells GLVSOD\HGEHWWHUSKHQROGHJUDGLQJHI¿FLHQFLHVWKDQIUHHO\ suspended cells after 18 hours. The immobilised cells ZHUHSURWHFWHGE\WKHSRO\PHULFJHODQGOHVVH[SRVHGWR heavy metals, thus reducing the chance of heavy metals
*HOODQJXP KUV Phenol degraded (g/mL) Phenol degradation rate (g/mL/hr) Percentage of phenol degradation (%)
Free cells (48 hrs) Maximum cell [Log 10(CFU)] Phenol degraded (g/mL) Phenol degradation rate (g/mL/hr) Percentage of phenol degradation (%)
Free cells (18 hrs) Maximum cell [Log 10(CFU)] Phenol degraded (g/mL) Phenol degradation rate (g/mL/hr) Percentage of phenol degradation (%)
.LQHWLF parameters/ performance
Table 1: Comparison of the kinetic parameters of phenol degradation by free and immobilised Acinetobacter VWUDLQ$412/LQWKHSUHVHQFHRIYDULRXVKHDY\PHWDOVDW 1 ppm. Values are mean ± standard deviation (n = 3)
Effects of heavy metals on phenol degradation by Acinetobacter sp. 249
interrupting the degradation process (Chung et al., 2003). The application of immobilised cells in bioremediation exhibits many advantages over free cells, including the stability of active cells, recovery of cells, and reusability of the immobilised system (Yun et al., 2009; Ahmad et al.,
September 2017
250 2
Cr6+ LV D XQLTXH WUDQVLWLRQ PHWDO LRQ ZKLFK KDV EHHQHVWDEOLVKHGWREHELRORJLFDOO\VLJQL¿FDQWRQOLYLQJ 2 RUJDQLVPVDWDOOOHYHOV+RZHYHUDWKLJKFRQFHQWUDWLRQV 3 4 it inhibits the biodegradation of organic pollutants 5 .RXUWHYet al $OEDOGDZLet al., 2015) including SKHQRO $O'H¿DU\ 5HGG\ ,QWKHHQYLURQPHQW pollution due to Cr6+ DQG LWV FRPSRXQGV LV ZLGHVSUHDG because of their application in industry as dyes, pigments, and refractory material (Zakaria et al., 2012). It appears that this source of pollution is the same as phenol pollution. Additionally, chemical pollution due to phenol and Cr2+ in the ocean has been increasing in recent years in the China Sea (Zhang et al., 2007). According to a previous study, Cr2+ is more toxic on *UDPQHJDWLYH EDFWHULD WKDQ *UDPSRVLWLYH EDFWHULD DW 1 ppm (Ross et al., 1981) and the toxicty of chromium to Acinetobacter VSVWUDLQ$412/D*UDPQHJDWLYH 6 EDFWHULXPXWLOLVHGLQWKLVVWXG\DI¿UPVWKLVREVHUYDWLRQ 7 Hg2+ is considered the most toxic non-radioactive metal in the environment and is toxic in any form
September 2017
ŽŶƚƌŽů
ŽŶĐĞŶƚƌĂƚŝŽŶŽĨƉŚĞŶŽů;Őͬ>Ϳ
Ϭ͘ϲƉƉŵ Ϭ͘ϳƉƉŵ
Ϭ͘ϰ
Ϭ͘ϴƉƉŵ Ϭ͘ϵƉƉŵ
Ϭ͘ϯ
ϭ͘ϬƉƉŵ
Ϭ͘Ϯ Ϭ͘ϭ Ϭ͘Ϭ
Ϭ
ϲ
ϭϮ /ŶĐƵďĂƚŝŽŶƚŝŵĞ;ŚŽƵƌƐͿ
ϭϴ
Ϯϰ
Figure 2: The effect of 0.6 to 1.0 ppm of chromium on phenol biodegradation by
Figure 2: The effect of 0.6 to 1.0 ppm of chromium on phenol biodegradation by immobilised Acinetobacter sp. strain $412/
a) (a) ŽŶƚƌŽů
Ϭ͘ϱ
Ϭ͘ϭƉƉŵ ŽŶĐĞŶƚƌĂƚŝŽŶŽĨƉŚĞŶŽů;Őͬ>Ϳ
In this experiment, at all concentrations studied, a ODJSKDVHZDVREVHUYHGDWWKHEHJLQQLQJEHIRUHSKHQRO GHJUDGDWLRQZDVREVHUYHG )LJXUH 7KHFRPSOHWLRQRI phenol degradation at 0.6 and 0.7 ppm Cr6+ concentrations occurred at 20 and 22 hours, respectively. At 0.8, 0.9 and 1.0 ppm concentrations complete degradation occurred at 24 hours. The results indicate that immobilisation of 3 4 cells in gellan gum beads protected the Acinetobacter sp. VWUDLQ$412/IURPFKURPLXPWR[LFLW\ZLWKKLJKHU concentrations requiring an additional incubation period for complete degradation. In this case, the incubation time needed to be increased from 18 to 24 hours. The presence RIDODJSKDVHLQGLFDWHVWKDWFHOOVZHUHDGMXVWLQJWRWKH toxicity of chromium through metabolic adaptation EHIRUH SKHQROGHJUDGLQJ PHWDEROLVP VWDUWHG *HOODQ 1 gum offers protection to heavy metal toxicity through YDULRXVZD\V Ϳ
2012). Since Cr6+ and Hg2+ inhibited phenol-degrading DFWLYLWLHV RI LPPRELOLVHG FHOOV LQYHVWLJDWLRQV ZHUH FDUULHGRXWWR¿QGWKHHIIHFWRIGLIIHUHQWFRQFHQWUDWLRQV of Cr6+ and Hg2+ (0.1 to 1.0 ppm) on phenol degradation after 18 hours.
S.A. Ahmad et al.
Ϭ͘ϳƉƉŵ
Ϭ͘ϰ
Ϭ͘ϴƉƉŵ Ϭ͘ϵƉƉŵ
Ϭ͘ϯ
ϭ͘ϬƉƉŵ
Ϭ͘Ϯ Ϭ͘ϭ Ϭ͘Ϭ
Ϭ
ϰ
ϴ
ϭϮ ϭϲ ϮϬ /ŶĐƵďĂƚŝŽŶƚŝŵĞ;ŚŽƵƌƐͿ
Ϯϰ
Ϯϴ
Figure 3: The effect of (a) 0.1 to 0.5 ppm and (b) 0.6 to 1.0 ppm of mercury on phenol
Figure 3: The effect of (a) 0.1 to 0.5 ppm and (b) 0.6 to 1.0 ppm of mercury on phenol biodegradation by immobilised AcinetobacterVSVWUDLQ$412/
Journal of the National Science Foundation of Sri Lanka 45(3)
Journal of the National Science Foundation of Sri Lanka 45(3) 0.1
Control
0.2
0.3
0.4
&RQFHQWUDWLRQ SSP 0.5
0.6
0.7
0.8
0.9
1.0
71.40 ± 7.48
59.80 ± 4.72
16.61 ± 0.00
44.20 ± 6.17
12.28 ± 0.00
74.80 ± 0.94
20.78 ± 0.00 73.80 ± 0.69
20.50 ± 0.00
62.80 ± 0.39
17.44 ± 0.00
63.60 ± 0.76
34.80 ± 1.73
9.67 ± 0.00
33.00 ± 5.24
9.17 ± 0.00
34.40 ± 0.90
9.56 ± 0.00
27.20 ± 3.22
7.56 ± 0.00
83.00 ± 2.08
80.20 ± 5.97
19.83 ± 0.00
100 ± 0.03
99.80 ± 0.10
22.28 ± 0.00
17.67 ± 0.00
99.80 ± 0.17
27.72 ± 0.00
23.06 ± 0.00
99.80 ± 0.06
27.72 ± 0.00
27.78 ± 0.00
99.60 ± 0.09
27.72 ± 0.00
318.00 ± 0.00 174.00 ± 0.01 165.00 ± 0.04 172.00 ± 0.01 136.00 ± 0.02
99.60 ± 0.20
99.80 ± 0.05
27.67 ± 0.00
500.00 ± 0.00 415.00 ± 0.02 374.00 ± 0.01 369.00 ± 0.00 314.00 ± 0.00
27.67 ± 0.00
27.72 ± 0.00
21.40 ± 2.92
5.94 ± 0.00
107.00 ± 0.02
46.80 ± 3.42
13.00 ± 0.00
499.00 ± 0.00 498.00 ± 0.00 498.00 ± 0.00 499.00 ± 0.00 499.00 ± 0.00 499.00 ± 0.00 401.00 ± 0.04 357.00 ± 0.05 299.00 ± 0.03 221.00 ± 0.04 234.00 ± 0.02
1RWH 3KHQROPHGLDZLWKRXWWKHSUHVHQFHRIKHDY\PHWDOVZHUHXVHGDVWKHFRQWURO Phenol degradation expressed as a percentage of 0.5 g phenol
Hg Phenol degraded (g/mL) Phenol degradation rate (g/mL/hr) Percentage of phenol degradation (%)
Cr Phenol degraded (g/mL) Phenol degradation rate (g/mL/hr) Percentage of phenol degradation (%)
.LQHWLF parameters/ performance
Table 2: The effect of different concentrations of chromium and mercury on phenol biodegradation by immobilised AcinetobacterVSVWUDLQ$412/DWKRXUV9DOXHVDUHPHDQVWDQGDUG deviation (n = 3)
Effects of heavy metals on phenol degradation by Acinetobacter sp. 251
September 2017
252
(Abdel-Salam et al., 2010). In Malaysia, the main sources of Hg2+LQULYHUZDWHUVDUHXUEDQDQGDJULFXOWXUDO UXQRIIV HIÀXHQW IURP LQGXVWULHV GRPHVWLF GLVFKDUJHV VHZDJH WUHDWPHQW SODQWV HDUWKZRUN FRQVWUXFWLRQV DQG pig farms (DOE, 2002). This heavy metal also appears in phenol-polluted environments. Hence, the effect of Hg2+ RQ SKHQRO GHJUDGDWLRQ ZDV VWXGLHG ,Q WKLV VWXG\ the presence of 1 ppm Hg2+ inhibited 100 % of bacterial JURZWKDQGSKHQROGHJUDGDWLRQE\IUHHFHOOVDQGPRUH than 70 % of phenol-degrading activities by immobilised cells. Hg2+ concentrations ranging from 0.1 to 1.0 ppm DIIHFWHGSKHQROGHJUDGDWLRQ S 7DEOH $ERYH 0.5 ppm, the metal inhibited more than 60 % of phenolGHJUDGLQJ DFWLYLW\ DQG WKLV FDQ EH FODVVL¿HG DV YHU\ detrimental (Ahmad et al., 2015). But, the inhibitory effect can be overcome by prolonging the incubation time for immobilised AcinetobacterVSVWUDLQ$412/ from 18 to 28 hours (Figure 3). The inhibition of phenol degrading activities by 0.1 to 0.4 ppm of Hg2+ ZDV FRPSOHWHGLQKRXUV )LJXUHD IROORZHGE\SSP at 21 hours, 0.6 to 0.8 ppm at 22 hours, 0.9 ppm at 24 hours, and 1.0 ppm at 28 hours (Figure 3b). In previous studies, Hg2+ KDV VKRZQ DQ LQKLELWLRQ RI GHJUDGDWLRQ of phenolic compounds by inhibiting hydroxylases DFWLYLW\ VXFK DV K\GUR[\EHQ]RLF DFLGK\GUR[\ODVH (Rajasekharan et al., 1990) and aryl 2,4-dichlorophenol hydroxylase (Radjendirane et al., 1991). CONCLUSION *HOODQ JXPLPPRELOLVHG Acinetobacter sp. strain $412/ SURYLGHG H[FHOOHQW SURWHFWLRQ WR WKH inhibitory effects of 1 ppm As, Cu, Cd, Ni, Cr, Pb and +JRQWKHJURZWKRIWKHEDFWHULXPDQGWKHGHJUDGDWLRQ of phenol by this bacterium. The inhibitory effects of chromium and mercury on immobilised cells could be overcome by prolonging the incubation period. The range of concentrations of heavy metals utilised in this study is very similar to the concentration range of heavy metals detected in the environment according to several studies and reports (Shukor et al., 2008; DOE, 2010). The results indicate that the immobilised bacterium XWLOLVHG LQ WKLV VWXG\ FDQ EH DQ HI¿FLHQW FDQGLGDWH IRU SKHQRO ELRUHPHGLDWLRQ LQ VLWHV FRFRQWDPLQDWHG ZLWK heavy metals. Acknowledgement 7KLVZRUNZDVVXSSRUWHGE\WKH5HVHDUFK*UDQWV6FKHPH 58*6 8QLYHUVLWL3XWUD0DOD\VLD
September 2017
S.A. Ahmad et al.
REFERENCES 1. Abdel-Salam A.M., Al-Dekheil A., Babkr A., Farahna M. 0RXVD +0 +LJK ¿EHU SURELRWLF IHUPHQWHG mare’s milk reduces the toxic effects of mercury in rats. North American Journal of Medical Sciences 2(12): 569 – 575. 2. $KPDG6$.X$KDPDG.1(:DQ-RKDUL:/+DOPL 0,( 6KXNRU 0
