Monitoring Arsenic Contamination Through Gene Expression

Arsenic is a naturally occurring ubiquitous groundwater pollutant affecting millions of people worldwide.  Chronic consumption of inorganic arsenic is known to cause serious health effects including cancers, vascular disease, gangrene, among others illnesses. Arsenic is usually tightly bound to iron minerals, which are ubiquitous in soil and sediments.  However, microbial anaerobic respiration can cause arsenic release from soil by altering the geochemistry of arsenic-bearing iron minerals within the soil. In the absence of oxygen microbes can use both arsenic and iron minerals as a terminal electron acceptor. Consequently, arsenic is liberated from a soil-bound form to water-soluble form through microbial iron and arsenate reduction resulting in arsenic polluted water.  A model iron/arsenic reducer, Shewanella sp. ANA-3, is being used to investigate the molecular biological response to iron and arsenic.  Specially, a green fluorescence protein (GFP) transcriptional reporter strain was inserted in Shewanella sp. str. ANA-3 genome downstream of mtr operon (genes essential for iron reduction) in order to further study arsenic’s fate and transport in more complex environments (i.e mineral rich environment). This single strain will be introduced into artificial soil aggregates, systems that mimic a true environment.  Microscopy will be used to determine the association of metal-reducing Shewanella bacteria within arsenic-bearing minerals and show the spatial and temporal expression of mtr genes relative to arsenic-iron containing minerals. The ability of being able to monitor the fate of arsenic, facilitated by dissimilatory metal reducing bacteria, could aid in the tracking of arsenic in the environment thus reducing chronic arsenic poisoning.