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Sewage sludge microbiota can help clean up toxic tetrachloroethene pollution

A pair of environmental engineers at the National University of Singapore has found that many bacteria in common sewer water are able to detoxify tetrachloroethene. In their study in the journal ACS ES&T Engineering, Guofang Xu and Jianzhong He explored whether microbes in sewage might be able to break down chlorinated solvents, which could make detoxifying such water easier.

Tetrachloroethene is one of the chemicals used in dry cleaning solvents. Unfortunately, in addition to being flushed into sewer systems, it can contaminate the air and enter the soil when it rains; from there, it can make its way into groundwater and/or rivers and streams.

The researchers collected 84 samples of sludge from sewer water from 38 treatment plants in 15 cities across the U.S., Singapore and China. They then separated out the microbiota they found in each sample and tested them individually on their ability to break down the chlorocarbon tetrachloroethene, and in the process, convert it to ethane.

The researchers found that out of the 84 samples, 63 contained microbes that completely broke down and detoxified tetrachloroethene by converting it to ethane. More specifically, the process was found to be initiated by a diverse collection of organohalide-respiring bacteria, such as Dehalogenimonas, Dehalococcoids, Sulfurospirillum and Geobacter.

They suggest that finding microbes that break tetrachloroethene down means that they could perhaps become part of bioremediation efforts. The researchers note that the finding suggests that the bacteria have evolved to have the ability to break down chlorinated solvents, because in the past, they were not able to do so.

The researchers also conducted a genetic analysis of the bacteria that break down tetrachloroethene, searching most particularly for genes that encode for RDases, which are enzymes known for their ability to remove chlorine from chlorinated solvents. They found what they describe as multiple genes that encoded for such enzymes. The finding could lead to the creation of a system that includes bacteria as a means for cleaning sewer water around the world.