Founded in 1930, Chicago’s Shedd Aquarium is not just a popular tourist attraction. Its staff also aids in worldwide conservation efforts and conducts essential research on animal health and behavior, nutrition, genetics, aquatic filtration, and molecular and microbial ecology. Over the last four years, those staffers have been puzzled by the mysterious disappearance of an antiparasitic drug routinely added to the water in the aquarium’s quarantine habitat. Now, with the help of microbiologists at Northwestern University, they’ve cracked the case. The culprits: some 21 members of a family of microbes who were munching regularly on the medicine in the water, according to a recent paper published in the journal Science of the Total Environment.
The aquarium’s Center for Conservation and Research includes an Animal Care and Science Division, with a state-of-the-art animal hospital for monitoring the health of all the animals in the exhibits and treating them as necessary. (If you want to know how to give an electric eel an MRI, the center’s team has you covered.)
Since 2015, the center has been working on a special research project investigating aquarium microbiomes. Among other topics, the project involves studying microbial communities in aquarium bio-filters. Such closed aquatic systems can quickly become toxic, thanks to ammonia waste from the fish, and certain microbial communities can help keep those levels in check. But other microbes are less beneficial, as evidenced by the Case of the Missing Chloroquine.
Whenever the Shedd Aquarium acquires new animals, the creatures are first placed in the quarantine habitat to prevent them introducing any outside pathogens into the aquarium’s carefully controlled environment. Part of that process involves administrating chloroquine phosphate, usually by adding it to the habitat’s water. Staffers regularly monitor the chloroquine concentrations, which is how they noticed that those concentrations were usually much lower than expected—often too low to serve as an effective antiparasitic.
Enter co-author Erica M. Hartmann and her fellow microbial detectives from Northwestern University. They took samples of the quarantine habitat’s water, as well as swab samples from the walls and pipes of the habitat. They brought the samples back to their lab for extensive analysis. All told, they counted some 754 different microbes that called the habitat home, and the team quickly surmised that the chloroquine thief was among them.
“There are microbes in the water, obviously, but there also are microbes that stick to the sides of surfaces,” said Hartmann. “If you have ever had an aquarium at home, you probably noticed grime growing on the sides. People sometimes add snails or algae-eating fish to help clean the sides. So, we wanted to study whatever was in the water and whatever was stuck to the sides of the surfaces.”
Next, the researchers had to winnow down the suspects. First, they took cultures of each microbe and gave each only chloroquine as food. Alas, those results didn’t narrow the field that much. But a critical clue emerged from their chemical analysis of the leftover chloroquine: it was missing all the nitrogen.
“Carbon, nitrogen, oxygen and phosphorous are basic necessities that everything needs in order to live,” said Hartmann. “In this case, it looks like the microbes were using the medicine as a source of nitrogen. When we examined how the medicine was degraded, we found that the piece of the molecule containing the nitrogen was gone. It would be the equivalent to eating only the pickles out of a cheeseburger and leaving the rest behind.”
Eventually, Hartmann et al. were able to identify 21 potential perpetrators who flourished in the habitat’s pipes, some of which do not appear to have been previously studied. It’s still unclear which of those are scarfing up all the nitrogen in the chloroquine, but at least the aquarium now knows the issue lies in the pipes. Unfortunately, simply regularly flushing those pipes probably won’t fix the problem, since the microbes cling tenaciously to the sides. According to Hartmann, the habitat pipes will need to be scrubbed or possibly replaced altogether. Switching between freshwater and seawater could also help keep microbial populations in check in the future.
“Overall, our results expand the body of knowledge surrounding aquarium microbiomes and veterinary drug degradation, revealing how microbial ecology and chemistry can be integrated into future management of saltwater circulating enclosures,” the authors concluded. “Furthermore, these findings might illuminate phenomena occurring in other nitrogen-limited environments when nitrogen-containing anthropogenic chemicals are added.”