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Biodegradation of the metallic carcinogen hexavalent chromium Cr(VI) by an indigenously isolated bacterial strain.

Das AP, Mishra S - J Carcinog (2010)

Bottom Line: At about 50 mg/L initial Cr(VI) concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation.The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei.Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI).

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Biotechnology, Siksha 'O' Anusandhan University, Bhubaneswar, India.

ABSTRACT

Background: Hexavalent chromium [Cr(VI)], a potential mutagen and carcinogen, is regularly introduced into the environment through diverse anthropogenic activities, including electroplating, leather tanning, and pigment manufacturing. Human exposure to this toxic metal ion not only causes potential human health hazards but also affects other life forms. The World Health Organization, the International Agency for Research on Cancer, and the Environmental Protection Agency have determined that Cr(VI) compounds are known human carcinogens. The Sukinda valley in Jajpur District, Orissa, is known for its deposit of chromite ore, producing nearly 98% of the chromite ore in India and one of the prime open cast chromite ore mines in the world (CES, Orissa Newsletter).

Materials and methods: Our investigation involved microbial remediation of Cr(VI) without producing any byproduct. Bacterial cultures tolerating high concentrations of Cr were isolated from the soil sample collected from the chromite-contaminated sites of Sukinda, and their bioaccumulation properties were investigated. Strains capable of growing at 250 mg/L Cr(VI) were considered as Cr resistant.

Results: The experimental investigation showed the maximum specific Cr uptake at pH 7 and temperature 30°C. At about 50 mg/L initial Cr(VI) concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation. The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei.

Conclusion: Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI).

No MeSH data available.


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Temperature optimization for Cr(VI) degradation
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Figure 0004: Temperature optimization for Cr(VI) degradation

Mentions: Cr(VI) degradation is significantly affected by various process parameters, such as initial pH and incubation temperature. At optimum pH 7, Cr(VI) degraded from 50-0.76 mg/L reducing Cr(VI) by 98%. Optimal pH for growth of Cr(VI)-resistant bacteria was evidenced at 7.0–7.8.[1314] The effect of pH on Cr(VI) reduction by the bacterial strain Brevebacterium casei cultures were initially supplied with 50 mg/L of Cr(VI) with inoculum volume of 1 mL. The chromate reduction study was carried out using freshly prepared overnight culture incubated at 30°C with shaking at 200 rpm. The cultures were harvested after a 12–h incubation period. Using B. casei strain, Cr(VI) reduction occurred at a pH range of 4–9, but an optimum reduction was observed at pH 7. pH was adjusted with 1 M NaOH and 1 M HCl. It was observed from the experiment that the extreme pH (4 and 9) restricted bacterial growth and Cr(VI) reduction. pH and Cr(VI) reduction relationship was not surprising because chromate (CrO42−) is the dominant Cr(VI) species in an aqueous environment at pH 6.5–9.0.[16] However, because Cr(VI) reduction is enzyme-mediated, variation in pH will affect the degree of ionization of the enzyme, changing the protein′s conformation and affecting the enzyme activity. [18] At optimum pH 7, Cr(VI) degraded from 50–0.78 mg/L reducing Cr(VI) by 98%. Optimal pH for growth of Cr(VI)-resistant bacteria was evidenced at 7.0-7.8[1317]; Laxman et al. (2007) also reported that an optimum pH of 6-7 is needed for the reduction of hexavalent Cr by Streptomyces griseus. Again Donati et al. (2003) suggested that the cultures at pH 6.0 and 7.0 showed lag phases shorter than those at pH 5.0. At pH 6.0, cultures had the highest free bacterial populations and the highest Cr reduction values. It is demonstrated that maximum Cr(VI) degradation occurred at 30°C reducing Cr(VI) from 50–0.6 mg/L[1315] at an optimal temperature of 30–37°C for Cr(VI) reduction. As evident from the experimental values, the suitable temperature and pH for hexavalent Cr reduction are 30°C and 7, respectively [Figures 4, 5].


Biodegradation of the metallic carcinogen hexavalent chromium Cr(VI) by an indigenously isolated bacterial strain.

Das AP, Mishra S - J Carcinog (2010)

Temperature optimization for Cr(VI) degradation
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2957624&req=5

Figure 0004: Temperature optimization for Cr(VI) degradation
Mentions: Cr(VI) degradation is significantly affected by various process parameters, such as initial pH and incubation temperature. At optimum pH 7, Cr(VI) degraded from 50-0.76 mg/L reducing Cr(VI) by 98%. Optimal pH for growth of Cr(VI)-resistant bacteria was evidenced at 7.0–7.8.[1314] The effect of pH on Cr(VI) reduction by the bacterial strain Brevebacterium casei cultures were initially supplied with 50 mg/L of Cr(VI) with inoculum volume of 1 mL. The chromate reduction study was carried out using freshly prepared overnight culture incubated at 30°C with shaking at 200 rpm. The cultures were harvested after a 12–h incubation period. Using B. casei strain, Cr(VI) reduction occurred at a pH range of 4–9, but an optimum reduction was observed at pH 7. pH was adjusted with 1 M NaOH and 1 M HCl. It was observed from the experiment that the extreme pH (4 and 9) restricted bacterial growth and Cr(VI) reduction. pH and Cr(VI) reduction relationship was not surprising because chromate (CrO42−) is the dominant Cr(VI) species in an aqueous environment at pH 6.5–9.0.[16] However, because Cr(VI) reduction is enzyme-mediated, variation in pH will affect the degree of ionization of the enzyme, changing the protein′s conformation and affecting the enzyme activity. [18] At optimum pH 7, Cr(VI) degraded from 50–0.78 mg/L reducing Cr(VI) by 98%. Optimal pH for growth of Cr(VI)-resistant bacteria was evidenced at 7.0-7.8[1317]; Laxman et al. (2007) also reported that an optimum pH of 6-7 is needed for the reduction of hexavalent Cr by Streptomyces griseus. Again Donati et al. (2003) suggested that the cultures at pH 6.0 and 7.0 showed lag phases shorter than those at pH 5.0. At pH 6.0, cultures had the highest free bacterial populations and the highest Cr reduction values. It is demonstrated that maximum Cr(VI) degradation occurred at 30°C reducing Cr(VI) from 50–0.6 mg/L[1315] at an optimal temperature of 30–37°C for Cr(VI) reduction. As evident from the experimental values, the suitable temperature and pH for hexavalent Cr reduction are 30°C and 7, respectively [Figures 4, 5].

Bottom Line: At about 50 mg/L initial Cr(VI) concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation.The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei.Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI).

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre of Biotechnology, Siksha 'O' Anusandhan University, Bhubaneswar, India.

ABSTRACT

Background: Hexavalent chromium [Cr(VI)], a potential mutagen and carcinogen, is regularly introduced into the environment through diverse anthropogenic activities, including electroplating, leather tanning, and pigment manufacturing. Human exposure to this toxic metal ion not only causes potential human health hazards but also affects other life forms. The World Health Organization, the International Agency for Research on Cancer, and the Environmental Protection Agency have determined that Cr(VI) compounds are known human carcinogens. The Sukinda valley in Jajpur District, Orissa, is known for its deposit of chromite ore, producing nearly 98% of the chromite ore in India and one of the prime open cast chromite ore mines in the world (CES, Orissa Newsletter).

Materials and methods: Our investigation involved microbial remediation of Cr(VI) without producing any byproduct. Bacterial cultures tolerating high concentrations of Cr were isolated from the soil sample collected from the chromite-contaminated sites of Sukinda, and their bioaccumulation properties were investigated. Strains capable of growing at 250 mg/L Cr(VI) were considered as Cr resistant.

Results: The experimental investigation showed the maximum specific Cr uptake at pH 7 and temperature 30°C. At about 50 mg/L initial Cr(VI) concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation. The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei.

Conclusion: Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI).

No MeSH data available.


Related in: MedlinePlus