Journal Club

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Journal Club: Antarctic cyanobacteria show no changes due to warming—yet

Researchers used historic 110-year-old cyanobacterial mats from Robert Scott's Discovery Expedition to investigate how the bacteria compare to present-day samples. Image: © The Trustees of The Natural History Museum, London

Researchers used historic 110-year-old cyanobacterial mats from Robert Scott’s Discovery Expedition to investigate how the Antarctica bacteria compare to present-day samples.
Image: © The Trustees of The Natural History Museum, London

Captain Robert Scott’s Antarctic Discovery expedition took place over 100 years ago—and yet its participants recently racked up another contribution to science. Thanks to the samples of bacterial mats they collected from polar ponds—samples that were pressed, dried, and stored in London’s Natural History Museum—modern researchers have determined how those key biological communities have changed in the intervening century. As it turns out, not very much.

The results, recently published in Proceedings of the Royal Society B, suggest that these organisms have experienced little environmental change, or they have adapted to the environmental alterations they faced. But the bacteria could still be affected by future human activity or climate change, says study author Anne Jungblut, a polar microbiologist at the museum.

Cyanobacteria are also known as blue-green algae, though they come in orange and purple, too. They are the bedrock organism of ecosystems in Antarctica’s freshwater lakes and ponds, collecting energy from sunlight and weaving their filaments into thick mats. These mats then support communities of other bacteria, archaea, and protozoa.

Jungblut wondered if the types of cyanobacteria in these communities were affected by climate change and human activity in the area. To find out, she used the samples from Scott’s mission aboard the three-masted wooden ship Discovery as a baseline, and compared them to new samples she collected, from similar spots, in 2011 and 2012. She amplified and sequenced DNA for 16S ribosomal RNA genes, which act like a barcode to identify taxonomic groups, from both sets of samples. Jungblut found 340 “operational taxonomic units” between the two sample sets, with 267 OTUs in the Discovery samples and 312 in the modern ones.

Overall, the kinds of cyanobacteria making up the communities were quite similar. “It looks like a carbon copy,” says Warwick Vincent, a biologist at Laval University in Quebec City, Canada, who works on polar lakes but was not involved in this study.

That’s not entirely surprising, given the minimal climate change so far in Antarctica’s interior says Henry Sun, a microbiologist at the Desert Research Institute in Las Vegas, who also works in Antarctica but did not participate in the new research. Though warming ocean waters have caused large icebergs to calve off the continent’s edges—including one nearly the size of Delaware that was just announced today—the interior has remained relatively protected from climate change. Wind patterns resulting from ozone depletion also seem to have minimized the temperature changes on the continent.

That doesn’t mean climate change doesn’t make a difference. There is evidence for environmental change, such as rise in lake water level by several meters in recent decades, says Jungblut, and the ozone hole is shrinking. But Sun notes that with respect to changes in the cyanobacterial communities, “even 100 years may be still too short to see it.”

Jungblut had also predicted new, invasive species might permeate the modern samples. While novel OTUs were present, these were varieties typical of Antarctica, not temperate or tropical microbes that might have snuck in with scientists or tourists.

That may be because the kinds of organisms that succeed in these polar ponds must be quite hardy. Resident cyanobacteria tolerate the pitch-dark winters, freeze-thaw cycles, and sways in pH and salt levels. Plus, they’ve already filled the available niche with their mats. “It makes it very difficult for any new microbe on the block to get a foothold,” says Vincent.

Nonetheless, Antarctic travelers are careful not to tote in any invaders, scrubbing down their gear with bleach and disinfectants. Those protections will remain important as the climate continues to change, says Jungblut. With time, she warns, Antarctica’s lakes could potentially become more hospitable for invasive bacteria, or even insects, that would disturb the cyanobacteria-based ecosystem.

In the current study, Jungblut focused only on the rRNA genes to identify kinds of cyanobacteria. But researchers could also examine the other microorganisms in the communities, suggests Vincent. “They’re really just opening the door here to a really very interesting and fruitful area of research,” he says. Plus, Jungblut has stored her samples—as mats and purified DNA—in the museum’s freezer. Perhaps 100 years hence, scientists will access them to apply their own techniques.

Categories: Biochemistry | Earth, Atmospheric, and Planetary Sciences | Ecology | Environmental Sciences | Journal Club | Microbiology and tagged | | | | |
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