Courtney Toth is an emerging leader in anaerobic bioremediation. She holds a Ph.D. in Environmental Microbiology from the University of Calgary, and currently works in the Department of Chemical Engineering & Applied Chemistry at the University of Toronto. Courtney’s research focuses on uncovering novel microorganisms and microbial processes that break down groundwater pollutants, most notably petroleum chemicals, and applying this knowledge to enhance natural bioremediation processes. In 2022, she was awarded the Mitacs Award for Commercialization for her role in developing first-of-their-kind bioaugmentation cultures for anaerobic treatment of BTX, in partnership with SiREM.

What was it that first piqued your interest in anaerobic bioremediation and environmental microbiology?

I first learned about bioremediation late in my undergraduate studies. My friends and I were exploring electives and stumbled across this strange-sounding course called “Petroleum Microbiology”. We gave it a go and 20 minutes in, I was hooked. I was especially taken by anaerobic hydrocarbon bioremediation and asked (begged?) my course instructor, Lisa Gieg, to take me on as a project student. That was the start of an incredible seven years of research under her supervision, from BSc to PhD. My thesis examiner was none other than Elizabeth Edwards, who coincidentally was looking for a postdoc to field test an anaerobic bioaugmentation culture that degrades benzene. And before I knew it, I was off to Toronto!

What sorts of problems do anaerobic BTX bioaugmentation cultures solve?

Hydrocarbons are ubiquitous in nature and as a result so are microbes who specialize in “eating away” at them. In general, this natural equilibrium maintains both at very low concentrations, but influxes of hydrocarbons from spills or oil releases tip the balance. Intrinsic microbial communities can respond to these influxes, but their effectiveness depends on a) how fast key cells can proliferate and b) whether microbial growth conditions can be sustained. The growth of anaerobic BTX degraders – but especially benzene degraders – is often slow to take off, resulting in slow rates of biodegradation and long remediation timeframes. We don’t yet fully understand what limits microbial growth at some sites but not others, but the cause doesn’t seem to be linked nutrient or electron acceptor availability. We’ve recently identified competitive enzyme inhibition, high cell decay rates, and oxygen toxicity as more likely possibilities. There are likely many other factors still to be discovered.

Bioaugmentation is designed to overcome this initial numbers barrier by injecting high concentrations of active specialized microbes into a contaminated site. The cultures we have developed contain hundreds of species of bacteria and archaea, but they can be categorized into one of four groups: hydrocarbon degraders, methanogens, syntrophs, and recyclers. Each of these groups has a distinct role in sustaining anaerobic hydrocarbon biodegradation activity, both in our cultures and in intrinsic microbial communities. Should any of these groups be missing or are in low abundances at a site, bioaugmentation can help fill the gap and facilitate faster anaerobic BTX degradation rates.

Anaerobic biodegradation of BTEX was first reported decades ago by Elizabeth Edwards and others, can you explain why it takes so long to develop these cultures for field application?

Bioaugmentation was in fact being marketed for anaerobic treatment of BTEX shortly after its discovery, but there simply wasn’t enough fundamental understanding of how anaerobic biodegradation processes worked to develop reliable cultures. We first had to resolve the underlying biochemistry behind these degradation pathways (an endeavor that is still underway for benzene!), which microbes were catalyzing these reactions, and how these microbes were distributed in nature. It was only in the last 10 or so years that we realized that anaerobic benzene and BTEX degraders are highly specialized – akin to how certain Dehalococcoides are uniquely adapted to only a few chlorinated substrates – and are widely distributed in anoxic environments. The same microbial communities were popping up everywhere anaerobic BTEX degradation was prevalent, with nearly identical compositions to those found in established enrichment cultures. That was the key “aha!” moment that led Elizabeth, myself, and others to revisit bioaugmentation for anaerobic hydrocarbon degradation.

So much has happened since then. Small research cultures were scaled up to industrial volumes. They went through rigorous bench-scale testing to validate the feasibility of this technology for BTEX. Massive regulatory documents were drafted and reviewed by the federal government, and injection permits had to be approved before we could start our first field trial. Today there are close to a dozen pilot tests underway across North America. It’s been a massive accomplishment to get this far.

Is there a bioremediation challenge that comes to mind that you see as key to your future research?

There is certainly no shortage of bioremediation challenges that need to be addressed, but I think many of them present the same research questions. What is preventing key pollutant-degrading microbes from proliferating in situ? What is the feasibility of overcoming those obstacles? And can we work around unavoidable obstacles without disrupting existing biodegradation processes? We still have a ways to go breaking down the fundamentals of bioremediation, and studying enrichment cultures, in my eyes, is still the gold standard for disseminating this knowledge. Better site characterization and routine adoption of molecular testing will also help. In the end, nature always finds a way.

What is the main piece of advice that you give to undergraduate students or perspective graduate students that are interested in pursuing a career in bioremediation research?

Bioremediation is interdisciplinary by nature and necessitates researchers to think broadly and work cooperatively. Seek out opportunities that expose you to many different aspects of the problem at hand. Ask questions. Take chances. Learn to be comfortable with making mistakes. Get messy.

What is your favourite part about working in academia/research?

The people! Research is a team sport, and the most effective teams are the ones who are open to collaborate and build each other up. I’ve been lucky to have been trained under and worked alongside countless scientists and engineers who share this value – people like Lisa and Elizabeth. And let us not forget the many students, technicians, and staff who make this research possible.

What do you enjoy doing outside of your job?

I’m a little kid at heart. I like to sing and dance when nobody’s watching. I doodle all over my notes. I daydream about traveling to far off places and going on adventures. I love a fast roller coaster.

Contact: courtney.toth@utoronto.ca