Burn, bacteria, burn: A fiery ghost town holds promising microbial secrets
For the past 57 years, the town of Centralia has been burning. Hundreds of feet below the town, a series of anthracite coal fires smolder in an area the size of seven Disneylands. Belching forth carbon monoxide, sulfurous compounds, and toxic gas, these anthracite fires have transformed lush Pennsylvania countryside into a landscape pockmarked with deserted strip mines, sinkholes, and a ghost town where Centralia once stood.
But it wasn’t always this way. In the early 1960s, Centralia boasted over 2,000 residents. Nestled on top of a rich vein of slow-burning anthracite coal, this Pennsylvania town also nurtured a robust and resilient mining industry. It survived a rash of gang violence in the late 19th century. It outlasted the Great Depression. But in 1962, Centralia met its match in “the worst underground mine fire in the United States,” to quote one Bureau of Mines scientist.
Although the exact origin of the anthracite fires is disputed, many believe that they began when Centralia officials decided to clean up a residential trash dump by burning the refuse. However, unbeknownst to the officials, the trash dump was located close to an abandoned coal mine. When they ignited the refuse, an underground coal seam caught flame. Rapidly, the fire began to spread throughout the mining tunnels that honeycombed Centralia. Several efforts to put out the blaze ensued, all of which were ultimately unsuccessful. Fueled by numerous boreholes and fissures providing an unlimited oxygen supply, the fires raged rampant, forcing Centralia residents to abandon their homes and extinguishing its once-vibrant industry.
Today, there are no plans to eliminate the anthracite fires and repopulate the fire zones. Most modern maps no longer even mention Centralia. Current predictions for how much longer they will burn — based on available coal resources and Centralia geography — estimate that the fires will continue for at least another 250 years.
But Centralia’s tragic story offers more than a valuable history lesson; it also provides an intriguing opportunity for scientific inquiry. Although Centralia’s human population has all but disappeared, a completely different population shift occurred among its microbial inhabitants. An important and active area of research is investigating how Centralia’s soil microbes have changed in response to variable soil temperatures.
What makes Centralia the perfect place to conduct these types of studies is how the anthracite fires spread and retreat. Every year, the fire front advances between 10 to 23 feet (3 to 7 meters) along subterranean seams of coal, heating up new soil areas to temperatures as high as 175 degrees Fahrenheit (80 degrees Celsius) while allowing older landscapes already exposed to the fires to return to normal. This pattern of exposure to and then rehabilitation from extreme thermal disturbance creates an exceptional environment to study what biological principles guide ecological responses to man-made stress.
Currently, a research team led by Ashley Shade from the University of Michigan is attempting to better understand these principles by studying changes in soil bacteria populations. By collecting samples of Centralia soil before, during, and after exposure to the subsurface anthracite fires, Shade and her colleagues try to answer important questions about the effects of the fire on Centralia’s microbes: What similarities and differences exist among the different soil samples? How does anthracite fire exposure affect bacterial diversity and resilience? And did any bacteria even survive their first fire exposure?
Although Shade’s research team found that bacteria did in fact survive, they noticed that the surviving microbes were very different from the original population. After fire exposure, they found many thermophiles (a subtype of bacteria that thrive in extremely hot environments) such as Chloroflexi, Firmicutes, and Armatimonadetes. Similar thermophiles are common in Icelandic hot springs. So with this discovery came a conceptual problem: How had the thermophiles — which could never have thrived in a pre-1962 Centralia — arrived in Centralia in the first place? Did they somehow come from as far away as Iceland, or could they have been there all along?
To answer this question, Shade turned to the idea of a microbial seed bank. In plant science, a seed bank is a collection of different plant seeds curated with the goal of preserving genetic diversity. By protecting rare and valuable plant species in a seed bank, scientists can ensure that plant populations remain more diverse and better able to respond to extreme environmental change. A famous example is the Svalbard Global Seed Vault in Norway, which was developed in 1984 with this goal in mind.
In microbiology, a similar strategy is used by bacteria to ensure survival against unpredictable environmental changes that occur too quickly for advantageous mutations to accumulate and for evolution to subsequently act on the bacterial population. Research by other microbiologists has shown that in soil, many different microbes are present, but not necessarily “alive.” Since a bacterial cell can exist in three different phases — activity, dormancy, or death — bacterial populations develop as a seed bank, or a mixture of bacteria scattered among these phases. In each seed bank soil sample, there are groups of bacteria that are fulfilling normal active processes, such as eating and growing, alongside inactive bacteria that no longer perform these processes but are also not dead. Instead, it’s as though these dormant bacteria are “sleeping,” waiting for the perfect moment to reanimate and populate the environment.
Shade’s group hypothesized that the thermophiles’ post-fire activity was an instance of dormant bacteria “waking up.” Before the fires, Centralia soil had developed a microbial seed bank over the course of many years. Whether arriving from faraway places by wind or being deposited by local bacteria during hard times, a vast and diverse host of microbes was developed. As long as soil temperatures remained within a normal range, non-thermophile bacterial species were active and thermophile bacterial species remained dormant. However, once these sampled soil areas were exposed to the anthracite fires, thermophile bacterial species became active and non-thermophile bacterial species became dormant or died out. Based on this realization, Shade’s group was able to conclude that Centralia’s microbial seed bank had likely contained thermophiles even before 1962; these bacterial species had simply been waiting for the perfect conditions to break dormancy.
More than just presenting an example of microbial seed banks in action, Centralia also provides a rare opportunity to discover new antibiotics and anti-cancer drugs.
For example, some soil bacteria are prolific producers of antibiotics such as tetracycline and streptomycin. By isolating these clinically useful antibiotics from bacteria, scientists can develop tools to resolve bacterial infections. However, many known antibiotics are rapidly becoming ineffective. The bacteria these compounds are meant to control can develop mutations that allow them to be resistant to antibiotics and, as a result, near impossible to treat. Today, most minor injuries are not a death sentence because we have the antibiotics to prevent bacterial infection. However, as more bacteria develop a resistance to known antibiotics, a pressing need emerges for us to discover new and potent antibiotics.
A robust way to discover new antibiotics is by characterizing the antimicrobial activity of rare soil bacteria. Many pharmaceutical companies have already identified antibiotics derived from bacteria living in normal temperature environments. However, Centralia’s thermophiles haven’t yet been scrutinized. Since so few extreme environments like Centralia exist in the world, it is likely that the bacteria inhabiting Centralia soils exhibit unique and compelling characteristics still unknown to science.
At the moment, many research teams are interrogating Centralia’s thermophiles in the hopes of finding new antibiotics or anti-cancer drugs. Shade’s group, however, also focuses on another valuable aspect of Centralia’s microbes: Their ability to lend insights on how global warming and climate change will modify microbial communities in the future. Taken together, all of these research objectives hold incredible promise for our future, even if they emerged from a place of great tragedy.
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