178

Bioremediation for Sustainable Environmental Cleanup

Acidothiobacillus ferrooxidans, for instance, has demonstrated the ability to achieve industrial-scale

bioleaching (Zhang et al. 2018). Acidocella aromatica and Acidiphilium symbioticum demonstrated

the capability to reduce vanadium ions and biosorption of cadmium cations under extreme pH levels

(Okibe et al. 2016).

A more effective method for toxic metal removal could be accomplished by using a microbe’s

consortium. The bioremediation of these pollutants by using an acid-isolated acidophilic microbe

consortia was performed on a contaminated sediment site. An acidophilic microbial composed of

Acidothiobacillus thiooxidans, Leptospirillum ferrooxidans and Acidiphilium cryptum demonstrated

effectiveness in extracting over 90% of Cu²⁺, Cd²⁺, Hg²⁺ and Zn²⁺ (Beolchini et al. 2009)

(Table 10.3).

Halophilic bacteria provide significant benefits in the remediation of hazardous contaminants in

extreme saline environments. As marine bacteria can survive at high salinity, bioremediation using

marine bacteria may be a viable alternative for cleaning seawater composed of toxic metals. Vibrio

harveyi has shown a significant potential to acquire cadmium ions. The adsorption capacity was

observed to be up to 23.3 mg Cd²⁺/g dry cells (Abd-Elnaby et al. 2011). The other marine bacteria,

Enterobacter cloaceae, could make complexes with Cd, Cu and Co from mixed-salts solutions

(Iyer et al. 2005). In conjunction with marine bacteria, thermophilic microbes have high biosorption

capability, indicating these microbes have a high potential for removing contaminants from polluted

environments (Özdemir et al. 2013).

Another approach is to study new extremophilic bacterial enzymes: extremozymes, which

have peculiar structure-function properties such as stability at high temperatures, severe pH, high

ionic strength, in the presence of organic solvents and toxic metals (Cabrera and Blamey 2018).

Extremophilic bacteria such as Metallosphaera sedula, Leptospirillum ferriphilum and Sulfolobus

solfataricus have been sequenced, and segments containing the Hg-resistance gene merA have been

discovered.

Table 10.3. Efficiency of extremophiles in bioremediation of toxic metals.

Toxic Metal

Bioremediation

Mechanism

Extremophiles

Initial Conc.

Efficiency

References

As (III)

Bioleaching

Acidothiobacillus

ferrooxidans BY-3

-

35.9%

Chen et al. 2011

U (VI)

Bioleaching

At. ferrooxidans

100 mg L^–1

50%

Romero-González

et al. 2016

Cu (II)

Bioprecipitation

Acidothiobacillus

ferrivorans

50 mM

> 99%

Jameson et al. 2010

V(V)

Bioreduction

Acidocella

aromatica

1 mM

70%

Okibe et al. 2016

Cd (II)

Bio-accumulation

Vibrio harveyi

30–60 mg L^–1

84%

Chakravarty and

Banerjee 2012

Biosorption

Acidiphilium

symbioticum H8

250 mg L^–1

248.62mg Cd

(II)/g biomass

Abd-Elnaby et al.

2011

Enterobacter

cloaceae

100 mg L^–1

65%

Iyer et al. 2005

Geobacillus

thermantarcticus

50 mg L^–1

85.4%

Özdemir et al. 2013

Anoxybacillus

amylolyticus

50 mg L^–1

74.1%

Özdemir et al. 2013

Cr (VI)

Bioreduction

Pyrobaculum

islandicum

600 µM

100%

Kashefi and Lovley

2000