A research team has stumbled upon a bug that feasts on arsenic. Present in the root nodules of black gram, the bacteria increases soil fertility and fixes nitrogen. It could be an effective way of bioremediation of arsenic from contaminated soil, says a team of researchers from iit Kharagpur and Vidyasagar University, Midnapore, West Bengal. They isolated a tolearant strain of rhizobium species from the root nodules of plants growing in contaminated soil.

For the study, the bacteria isolated from the root nodules of the plant were cultured and exposed to sodium arsenate solution. "We found that the bacteria digested the arsenate and some of it was loosely left attached to cell surface," said Ananta Kumar Ghosh, lead researcher from the Department of Biotechnology, iit, Kharagpur. The rhizobium isolate had higher arsenate tolerance than other micro-organisms.

The study, published in Journal of General and Applied Microbiology (Vol 54, No 2), threw light on a gene's role in the bug's tolerance property. The gene codes a protein that can sense arsenic. The researchers say the bug's cell wall is rich in complex organic molecules like lipopolysaccharides and phospholipids. The arsenate might bind to the bug's phospholipid-rich cell wall.

The study assumes importance because arsenic-contaminated groundwater has caused several deaths in West Bengal and has caused millions to suffer from skin lesions, cancers and other diseases. Studies have shown that arsenic enters the human body through crops and vegetables grown in arsenic-contaminated soil. Anisur Rahaman Khuda Bukhsh of Kalyani University, West Bengal, however, says that though the research is commendable, it has "limited practical applications". Though the bug is naturally found in root nodules of black gram, it remains to be seen whether it could be incorporated into other crop plants or cereals, he added.

Source : Down To Earth, July 2008