Is Antarctic wildlife at risk from human E. coli?

Posted on July 5, 2016   by Anand Jagatia

Antarctica is the only continent on Earth without a native human population. But at any one time, there are still thousands of people living there, most of them scientists. During the course of their research, it’s inevitable that these scientists will produce human waste. So where does all this sewage go?

The answer depends on the base. The 53 countries with stations on Antarctica are all bound by the Antarctic Treaty, which regulates, among other things, how people on the continent dispose of their sewage. The recommendation is to remove sewage from Antarctica completely. But if that isn’t possible, the Treaty permits bases to dump their sewage directly into the sea.

For one of the most pristine environments on the planet, these regulations may seem a tad light. While many bases do treat their sewage biologically or chemically, or even shipping the resultant sludge back home, up to a third don’t treat their waste at all. Others simply macerate (blend up or puree) the sewage before discharging it into the sea.

The impact of this waste on the environment is potentially huge. Untreated sewage can disrupt the nutrient, pH and oxygen levels in the sea, release damaging pollutants like metals into the water, and also introduce large quantities of foreign microbes into the marine environment. These bacteria have the potential to impact ecosystems and, if pathogenic, could cause disease in Antarctic wildlife.

Now, new research carried out on Davis Station, an Australian research base, shows that bacteria and genes that were previously only found in human environments are integrating into the Antarctic microbiome. The problem is no longer just about sewage pollution. It’s about microbial and genetic pollution too.

“We were interested in seeing whether E. coli were surviving in the environment,” says study leader Dr Michelle Power, from Macquarie University in Australia. “So we obtained samples from water that came out from the [Davis Station] sewage plant. We also sampled wildlife species, like elephant seals, Weddell seals and Adelie penguins.”

Once the samples had been collected, Michelle and her colleagues analysed them to determine whether the E. coli were naturally present in the area, or had been introduced by humans. They did this by looking for the presence of different ‘virulence factors’ – molecules that microbes use to colonise their hosts – which can be used to trace the species bacteria likely came from. For example, E. coli that usually cause disease in humans will have a different suite of virulence factors to those that usually live in animals and do not cause harm.

The team found that the distribution of virulence factors in the Antarctic E. coli was more similar to that seen in humans rather than Antarctic animals. They also detected the presence of integrons (genetic units that allow bacteria to share genes) that were identical to variants seen in human clinical contexts. The integrons are important as they carry genes that cause antibiotic resistance, which the researchers also found in the E. coli of Antarctic shellfish.

Taken together, these results suggest that at least some of the strains now found in the Antarctic ecosystem have a human faecal origin. As well as this, the researchers discovered two strains of E. coli in seals that are known to cause disease in humans and birds, which may pose a health risk for Antarctic wildlife.

“We’re putting genetic material [into Antarctica] that doesn’t normally exist there,” says Michelle. “I was surprised by how many different E. coli strains we found in Antarctica and the diversity of antibiotic resistance genes they carried. These genetic elements can play a major role in the evolution of microbes. So by introducing them, we’re potentially changing the evolutionary trajectory of the microbes there.”

So how much of a problem is this? Well, first it’s unclear what effect this shift in microbiome will have on Antarctic animal health or behaviour. But Michelle points out that even though E. coli is common in the human gut, it’s often much rarer in other animals such as seals and penguins, so its potential effects are unclear. Second, we don’t know how widespread this microbial pollution is on the rest of Antarctica – this particular study was based on sampling around just one station. And third, it’s unknown whether these newly detected bacteria are part of a temporary shift in the Antarctic microbiome, or a long-term change.

Future research is needed to address these questions, but Michelle says that the regulations for sewage disposal should be reconsidered in light of their findings. In the meantime, Davis Station has already begun to upgrade their sewage system to better handle waste.

“I’d like to take a wider look across the continent to see the extent that that we’ve impacted wildlife species and to what extent human E. coli have colonised Antarctica,” says Michelle.

Describing her experiences on the expedition, she says, “The fieldwork was fantastic, really special. For collecting animal samples, we’d jump in a helicopter and fly out to remote areas, some amazing places that people normally don’t get to see.

“We also collected our sewage in plastic bags, and took it back with us to the station.”