Bacteria solution to groundwater arsenic
Bangladesh scientist says the bugs use arsenic for energy

Scientists have identified a special group of bacteria responsible for breaking down arsenic in groundwater. This was disclosed by a Bangladeshi scientist conducting a study in the UK on the cause of naturally occurring arsenic release into groundwater table. The discovery may provide a possible solution to groundwater arsenic contamination that now exposes an estimated eight million people in 61 districts in Bangladesh to serious health hazards.
Millions of people, mostly in the rural areas, have developed various symptoms of poisoning from drinking arsenic-contaminated water from tubewells for decades.

The study by Farhana Islam, supervised by other researchers, showed the special group of bacteria 'gains energy by respiring (breathing), using the metal iron and arsenic containing minerals in the earth sediments'.
The young scientist said, "Our results show that these are the special anaerobic bacteria, as they don't need any oxygen to support their growth. They are known as metal-reducing bacteria. We are very interested in iron-reducing bacteria that use iron as their growth substrate, and can also use arsenic when the iron is used up."
The bacteria cause changes in the mineral structure of the sediments, leading to release of arsenic into groundwater, the study says.

Farhana, who studies in the Department of Earth Sciences and Williamson Research Centre for Molecular Environmental Science at the University of Manchester, told The Daily Star, "We are looking at how these processes of breaking down the mineral can be reversed so that the groundwater is safe to drink."
She elaborated, "With our results, we found that maximum amount of arsenic was released from contaminated sediment into groundwater in the absence of oxygen."
There were several hypotheses concerning the release of arsenic into the groundwater systems of West Bengal in India, where the researchers worked. Some suggested a role for aerobic bacteria (arsenopyrite oxidation), some suggested a role for metal-reducing bacteria while others considered the problem to be driven by geochemistry.

The scientists from Manchester University conducted experiments in their laboratory with sediments collected directly from an area of West Bengal affected by arsenic.
"We were the first group to combine geochemical, mineralogical and microbiological/molecular biology techniques to study this system, and have presented the first direct evidence to support a role for metal-reducing bacteria in arsenic release from the sediments. The organisms identified as playing a key role are iron reducing bacteria that can attack arsenic once they have exhausted iron as a growth element," Farhana explained.

Studies showed that this type of bacteria is unable to use oxygen for growth, rather they use different metals to support their metabolism. Metal-reducing bacteria 'breathe' metals such as iron to get energy from their food, in the same way humans breathe oxygen to break down food.
The iron-reducing bacteria use iron through the electron transport system in the anaerobic respiration and gain energy for their growth by reducing this iron. This process is known as dissimilatory iron-reduction.
Explaining the process of arsenic contamination, Farhana said instead of using oxygen, the anaerobic bacteria gain their energy by respiring, (breathing) using iron-containing minerals in the sediments, a process called iron reduction.

By doing this, the bacteria transfer electrons to iron oxide rust coating the sediments, causing changes in the characteristics of the minerals. And when the iron runs out, the bugs start to utilise other metals, such as arsenic, which occurs naturally. The chemistry of the arsenic is changed and the reduced arsenic is able to dissolve into groundwater, she said.