Arsenic contamination is one of the biggest problems in drinking
water all over the world. Groundwater contamination is primarily caused by microbes that
convert one form of arsenic into another form that can infiltrate
Environmental engineers are making it easier to identify the
bacterial species responsible for releasing a form of arsenic that
contaminates the water supplies of millions of people worldwide.
‘A genetic tool that makes it easier to identify which microbial species have the arsenic-converting genes has been developed by researchers.’
A team of Utah State University College of Engineering researchers
developed a new primer - a tool used in DNA amplification - that
simplifies the process of identifying bacteria found in soil and
Of interest are the bacteria species equipped with
arsenate reductase genes. The genes enable bacteria to transform
naturally occurring arsenic into a more toxic version of the element.
The team's findings were published in Applied and Environmental Microbiology
- a leading journal, covering topics in biotechnology, microbial ecology, food microbiology and industrial microbiology.
The authors explain that various bacteria transform, or reduce,
arsenic V - known as arsenate - into arsenic III - known as arsenite.
Arsenite is more toxic to humans and is more mobile, meaning it moves
through the environment more easily and can infiltrate groundwater.
Researchers say a better understanding of the microbial
ecosystems that release arsenite is an important first step in reducing
the prevalence of arsenic contamination in groundwater.
Dr. Babur Mirza, a researcher at USU's
Utah Water Research Lab and lead author on the study, said, "This new primer
makes it easier for us to see which species of bacteria are present in a
sample and whether they have the gene that we're looking for."
The new primer - a short strand of DNA that targets the arsenate
reductase gene - helps researchers identify which bacteria in a sample
have the genes. Without this primer, researchers had to first grow the
bacterial cells in a laboratory before extracting their DNA and
amplifying the gene. Such steps often reduced microbial diversity and
led to biased results.
"Now we can simply add the primer into the reaction and we get
quantifiable copies of the reductase genes," said Mirza. "The copied
genes show us which bacteria species are in the sample and tell us new
information about the diversity of arsenate-reducing microorganisms."
As part of the study, the team, led by co-author Dr. Joan McLean,
pulled groundwater samples from 20 privately owned wells located in
Northern Utah's Cache County. The results showed that 20% of the
wells surveyed had arsenate and arsenite concentrations above the
drinking water limit of 10 micrograms per liter. Researchers then tested
whether the samples containing high arsenite concentrations also had an
abundance of the arsenate reductase genetic material. Not surprisingly,
they found a direct match.
"We observed a significant correlation between reductase gene
abundance and arsenite concentrations in the groundwater samples," said
Mirza. "What this means is that wherever we find arsenite, we can expect
to find microbes with arsenate reductase genes and vice versa."
Mirza said the new primer successfully amplified the reductase
genes and made it possible for his team to see a broad diversity of
arsenate-reducing microorganisms. He said the new primers will be useful
for studying bacteria in a range of environments.
The authors say there are various implications to the study.
McLean said a complete picture of the diversity of arsenate-reducing
bacteria in a particular environment could lead to improved land use
practices and awareness of human activities that may exacerbate the
"With this new information describing the diversity of
arsenic-reducing microorganisms, we are further exploring relationships
between these organisms and their biogeochemical environments that
result in arsenic contamination of groundwater."