NBRI: Arsenic bioremediation using two soil bacteria

The bacteria increase bioavailability of metals, facilitate plant growth

Deformed fingers due to arsenic contamination.

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

What adds value to these strains ( Bacillus flexus and Acinetobacter junii ) is the fact that they can promote plant growth too.

Different forms of arsenic

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.

B. 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.

Plant growth promoters

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.

The paper published in the Journal of Applied Microbiology notes that these indigenous strains demonstrated the “potential to accumulate arsenic within the cells and transform it into less phytotoxic forms, making the strains more proficient candidate for bioremediation”.

More studies in the field are needed to validate the results.