News

• Using two indigenous strains of bacterium isolated from arsenic-contaminated field, researchers from CSIR-National Botanical Research Institute (CSIR-NBRI) and the University of Lucknow have shown that arsenic can be effectively removed from contaminated soil with the help of microbes.

Hazards of Arsenic contamination

• Arsenic is an element widely distributed in earth’s crust, and in groundwater in many countries.

• Long-term intake of arsenic contaminated water leads to arsenic poisoning or arsenicosis, with cancer of skin, bladder, kidney or lung or diseases of skin (colour changes, and hard patches on palms and soles), or blood vessels of legs and feet.

• Fresh evidence indicates possible association between intake of contaminated water to onset of diabetes, hypertension and reproductive disorders.

• In India, the states of West Bengal, Jharkhand, Bihar, Uttar Pradesh, Assam, Manipur and Chhattisgarh are reported to be most affected by arsenic contamination of groundwater above the permissible level.

• WHO’s provisional guideline value for arsenic in drinking water – 0.01 mg/l (10 μg/l).

Arsenic bioremediation

• The strains are named as Bacillus flexus and Acinetobacter junii.

• Several studies have pointed out that using arsenic-contaminated water for agricultural purposes can lead to increased concentration of arsenic in fruits and grains, proving toxic to humans.

• The researchers studied the two bacteria under different concentrations of arsenate and arsenite, the toxic forms of heavy metal.

• Arsenic treatment did not stunt or delay the growth of both the bacterial strains.

• flexus exhibited resistance to high levels (150 mmol per litre) of arsenate and A. junii to about 70 mmol per litre of arsenite.

• This is higher than previously reported arsenic tolerant bacteria and so were regarded as hyper-tolerant strains.

• Further gene detection studies pointed out that both the bacteria have a special ars C gene, which aids in arsenic detoxification.

Promotes plant growth

• The bacterial strains were further scrutinised to understand if they can help in plant growth too. In studies carried out in the lab, both the bacteria were able to solubilise phosphorus.

• Phosphate solubilising bacteria have been reported to increase phytoavailability of phosphate, thus facilitating plant growth.

• These two bacterial strains were also found to produce siderophores and ACC deaminase enzyme.

• Siderophore increase the bioavailability of iron and other metal ions in polluted soil environment and ACC deaminase is a well known plant growth promoting enzyme.

• These bacteria can live symbiotically in the roots of plants in arsenic- contaminated soils and help them uptake the required nutrients without causing toxicity.