AMERICAN CHEMICAL SOCIETY Exposure to endocrine-disrupting chemicals (EDCs), compounds that interfere with native hormonal receptors, has been associated with everything from obesity to cancer. EDCs are present in a variety of consumer products—bisphenol A (BPA), for example, can be found in some plastic containers. Although these compounds are not trivial to find, last month (January 11) in ACS Central Science, a team at the University of California, Berkeley, reported on a new method for detection, which it developed using Escherichia coli bacteria.
“There are many [endocrine-disrupting] compounds found in the environment now due to pollution, fracking and other kinds of industrial processes,” said study coauthor Ariel Furst, a postdoctoral fellow at UC Berkeley. These compounds “can have [a] detrimental effect on health, leading to diseases and [other] problems,” she added.
E. coli cells naturally express estrogen receptors on their surfaces. Taking advantage of this, Furst and colleagues created an “electrochemical sandwich assay” with two components: freeze-dried bacteria that had been engineered to display estrogen receptors on their surfaces and disposable electrodes, which the researchers modified with proteins that bind to the estrogen receptor only when EDCs are present. “The way the electrochemical technique works is that it basically just measures how much of your surface is blocked,” Furst explained. “In the presence of [an EDC], the E. coli binds to our electrode, which is modified with another protein, and then we can basically use electrochemistry to count the bacteria on the surface.”
“The approach is original and the reaction time is fast,” Jan Roelof van der Meer, a microbiology professor at the University of Lausanne in Switzerland who did not take part in the work, wrote in an email. “The test lacks the absolute specificity that antibodies can give, but here it is used as an advantage, because potentially multiple endocrine-disrupting chemicals can be measured simultaneously . . . some people see it as advantage; others find it difficult because you can never trace it back to an individual compound.”
The sensor was able to detect various EDCs with different structures, including BPA and diethylstilbestrol, the researchers reported. They also tested whether the sensor could detect EDCs in a consumer product. They compared a plastic baby bottle—which, despite its “BPA-free” label, does release EDCs when microwaved—to a glass one. After microwaving the bottles 10 times for two minutes each, the researchers were able to detect significant estrogenic activity in the plastic bottle, but not the glass one.
“I was amazed at how much estrogenic activity they detected,” said Wade Welshons, who studies endocrine disruptors at the University Missouri-Columbia and was not involved in the study.
“There are very good tests that exist but they require the growth of yeast or human cells or E. coli that all require specialized facilities. This has to be done in a lab and it takes several days,” Furst told The Scientist. “Ours can be applied in the field.”
Typically, it “takes two days for a transfection assay and seven days for a proliferation assay, [so] we’re going from days down to minutes,” Welshons said.
However, experts who were not involved in the study pointed out that use of this sensor does require some expertise. “This is not . . . like a glucometer where anyone takes a prick of their blood, sticks their blood on the electrode and sticks the electrode on the reader and that’s it,” said Robert Marks, a professor of biotechnology engineering at Ben Gurion University of the Negev in Israel who was not involved in the work. “What they’re asking for here is to do washes, wet the bacteria, mix it with the samples—so you need a technician that knows a little bit about what they’re doing.”
The group now hopes to adapt the sensors to detect other environmental chemicals as well. “I think the most exciting thing for us is our ability to . . . count bacteria on an electrode surface,” Furst said. “There are a lot of potential applications for that. . . . In addition to these other hormone receptors, we’re generally looking at what biomolecules we can put on electrodes to count bacteria.”
A. Furst et al., “Quantifying hormone disruptors with an engineered bacterial biosensor,” ACS Central Science, doi:10.1021/acscentsci.6b00322, 2017.