At an old steel site in Pittsburgh, bacteria evolved to survive – and eat – industrial pollution

Pittsburgh, once known as the Steel City, was a major industrial hub in the 19th and 20th centuries, powered by steel mills and coal-fired furnaces. These industries left behind a significant environmental legacy, including soil contaminated with toxic chemicals such as petroleum hydrocarbons and heavy metals. One such site is Hazelwood Green, a 178-acre former industrial area along the Monongahela River in Pittsburgh. For over a century, it housed steelmaking operations like the Jones & Laughlin Steel Co., employing thousands of workers. Today, Hazelwood Green is being transformed into a research and technology hub, but its soil remains contaminated with pollutants like benzene, toluene, ethylbenzene, and xylene—a group collectively called BTEX. These chemicals are toxic to humans and some are known carcinogens.

Brownfields are former industrial or commercial sites with contaminated soil, often abandoned or vacant. While redevelopment efforts focus on cleaning up these sites, another transformation has been happening beneath the surface for decades. Billions of microbes, including bacteria, inhabit these soils and have been adapting to the pollution over time. In Pittsburgh, some bacteria have evolved to survive and even consume industrial pollutants like BTEX. These microbes are part of a living ecosystem that has been responding to decades of contamination. The study of these microbes offers insights into how pollution shapes microbial communities and how they might help clean up contaminated sites.

Industrial pollution acts as an unintentional evolution experiment for microbes. Soil contains an extraordinary diversity of microorganisms, with billions of bacterial cells in a single gram. When pollutants like BTEX enter the environment, they create a new ecological challenge. Some bacteria may already have the ability to tolerate or even consume these pollutants, giving them a survival advantage. Over time, these bacteria become more common, and they can pass their pollution-degrading abilities to other bacteria through gene sharing. At Hazelwood Green, decades of industrial pollution have provided scientists with a natural experiment to study how microbes adapt to and degrade pollutants.

Researchers at Carnegie Mellon University are studying the microbes in Hazelwood Green’s contaminated soil to understand their role in pollution degradation. They collect soil samples from different depths and locations, preserving the soil layers in cylindrical cores. Using metagenomic sequencing, a technique that identifies all microorganisms in a sample directly from its DNA, they analyze the microbial communities. The goal is to identify bacterial genes associated with the degradation of BTEX and other hydrocarbons. By comparing historical contamination records with modern microbial communities, they aim to determine whether past pollution has left a lasting signature in these ecosystems.

To confirm which microbes can degrade pollutants like BTEX, researchers isolate bacteria from Hazelwood Green and other Pittsburgh sites and test their ability to use pollutants as food. In the lab, bacteria are grown in a minimal medium without traditional carbon sources but with pollutants like benzene or toluene as the sole carbon source. If the bacteria grow, it indicates they can consume the pollutant. This process helps identify microbes that could be used for bioremediation, a method of cleaning up pollution using living organisms. The researchers also partner with CMU’s AI Science Foundry, an automated lab, to screen thousands of bacteria simultaneously for their pollutant-degrading abilities.

Bioremediation, the use of microbes to clean up pollution, is already applied in cases like oil spills and wastewater treatment. However, it does not work equally well for all pollutants or sites. One challenge is identifying microbes that can degrade specific contaminants while thriving in the environmental conditions of the contaminated site. Studying microbes that have already adapted to pollution, like those in Hazelwood Green, provides a significant advantage. By understanding how these microbes metabolize pollutants, researchers aim to improve bioremediation techniques. This approach could make soil cleanup more effective and sustainable, especially as former industrial sites are repurposed for new uses.