Scientists at the National University of Singapore theorized that bacteria in sewage sludge might have detoxifying capacities because wastewater commonly contains chlorinated solvents such as tetrachloroethene, which would mean that microbes in sewage plants are frequently exposed to the pollutants and therefore may have evolved ways to digest them.
The researchers collected 84 sludge samples from 38 different wastewater treatment plants in 15 cities across China, Singapore, and the US. Using the microbiota extracted from these sludge samples, the study authors measured whether the bacteria could detoxify tetrachloroethene, converting it into ethane. Their findings surpassed their expectations.
“Remarkably, 63 out of 84 sludge microbiota samples from WWTPs [wastewater treatment plants] completely detoxified tetrachloroethene to ethene,” stated the authors in the paper. “These findings have significant environmental implications, particularly for the bioremediation of groundwater contaminated with chlorinated solvents.”
The researchers carried out a genetic analysis of the detoxifying bacteria, specifically looking for genes that code for RDases—enzymes that catalyze the removal of chlorine from chlorinated solvents such as tetrachloroethene. The results showed that multiple different genes encoding for such enzymes simultaneously coexisted within the sludge microbial communities.
This finding, the authors concluded in the paper, showed “a robust and versatile bioremediation capacity.”
The most abundant bacteria in the sewage sludge were Dehalococcoids, followed by Geobacter, Dehalogenimonas, Dehalobacter, and Sulfurospirillum. Knowing the bacterial strains and understanding the genetics that underpin their detoxification potential could prove to be a valuable tool, says Hideyuki Inui, an environmental biologist at Kobe University who was not involved with the new study. This understanding could allow scientists to genetically engineer bacteria to optimize their capacity for environmental cleanup, an approach that Inui thinks could be applied to other pollutants such as the so-called “forever chemicals” per- and polyfluoroalkyl substances (PFAS).
But this discovery is just one step on the way to full-scale bioremediation, says Inui. Using bacteria to rid waterways and other environments of pollutants such as tetrachloroethene is not as straightforward as simply introducing the microbes to their new location and leaving them to it.
“Bioremediation is difficult when applied to real-world contaminated states,” he warns. “Bacteria and nutrients need to be continuously applied to maintain their degradation activity.” Managing to do that without further disturbing the balance of a habitat is challenging and would need perfecting before deploying it at scale.