May 05, 2022

By Jennifer Yuricich ’00 Spotts

The mine fire already had been burning for 40 years underneath the ground where Tammy Tobin stood two decades ago to determine if she wanted to be part of a study. When she observed the anthracite smokers — steam laden with combustion products that deposit chemicals on the surface — the answer was clear to her.

“I was captivated and decided I wanted to be a part of this,” she recalled.

Tobin, department head and professor of biology, was approached by Susquehanna’s Department Head of Earth and Environmental Sciences Dan Ressler, who was recruiting a faculty member for the study. She and her team went on to conduct a 20-year study that led to the discovery of microbes that had never been described before. As the 2022 John C. Horn lecturer, she summarized their research in Centralia, Pennsylvania. Among her peers, students, alumni and interested faculty and staff, she explained the goal of the study: to determine how microbial communities change as a mine fire moves through an area — specifically the resistance, resilience and recovery of microbes in the soil.

Before the borough of Centralia, about an hour east of Susquehanna University, became a near ghost town, it was occupied by nearly 3,000 residents at its peak: during the mining production of anthracite coal. Tobin explained that in 1962, an above-ground trash fire accidentally ignited a surface-accessible coal seam and traveled through the coal deposit layers until it reached the mining tunnels.

“The coal that remained in that area, plenty of it, is a great fuel source for the fire, so it continues to burn,” Tobin said. “When that burns out, the mine shafts collapse and so does the ground above them.”

She showed pictures throughout the lecture of deep crevices in a former highway and pointed out how the crevice depth in one area changed dramatically in just eight years.

To determine their soil sampling sites, Associate Professor of Earth and Environmental Sciences Jennifer Elick took photos from an airplane of the same location during daylight and with an infrared camera at night. They plotted sites that were unaffected, would be affected and would recover from the underground fire. Their soil samples, some upwards of 750 degrees Fahrenheit, were filled with all kinds of chemicals, causing a big change to the soil environment.

“The gases that rose were filled with combustion products, like sulfur and nitrogen and arsenic. As gases rise to the surface, they cool and condense, depositing those products into the surrounding soils,” Tobin explained.

Team Discovers Previously Unknown Microbes 

They soon discovered that Centralia was the “hot bed” to study previously unknown thermophiles (microbes that require heat to divide and thrive). Thermophilic bacteria are usually rare in places like Centralia — but when its soil temperature soared, uncommon microbes became commonplace. Twenty-five percent of the bacteria they isolated had never been described before, by anyone.

These new bacteria also revealed new types of metabolism. It had previously been thought that ammonia-oxidizing bacteria could not survive above 25 degrees Celsius, but they were found in much warmer soils throughout Centralia. Tobin and her team determined the fire-affected soils have divergent microbial communities that, surprisingly, have smaller genomes than those in temperate soils. The small genomes may be optimized to the new environment, demonstrating an increased potential to metabolize mine fire products like nitrate and sulfate and a reduced potential for antibiotic competition strategies. They also found that as the mine fire moves into new areas, the microbial communities in recovered soils return to a “norm” that is different from unaffected soils.

Over the course of the study, their research was helped by scientific advancements. They initially used genetic fingerprinting — taking DNA fragments of the same size and cutting them with an enzyme at a specific DNA sequence to create a community DNA barcode as a rough way to study community diversity. They also identified the few bacteria that they could isolate in culture by sequencing a small gene shared by all bacteria, the 16S ribosomal RNA gene. However, these techniques could only identify a tiny fraction of the bacteria living in Centralia. Later they utilized shotgun metagenomics, where they were able to sequence the entire genomes of all of the bacteria present in the soil samples, further expanding their understanding of the complex ways in which Centralia’s bacterial communities respond to the mine fire.

Although Tobin will retire from Susquehanna in summer 2022, she will return to Centralia with Ashley Shade ’04 throughout the last year of the National Science Foundation grant. The mine fire continues to have a dramatic effect on the surface soils, and Tobin and her colleagues will monitor the soil bacterial communities as the fire spreads through new areas.

“Most excitingly, we will finally have the opportunity to use a technique called metatranscriptomics to determine how bacteria change actual gene expression — not just presence — in response to the fire-affected environment. This could lead to the discovery of new bioproducts and antibiotics, and will certainly form a model by which we can better understand bacterial resistance, resilience and recovery to other environmental warming events,” Tobin added.