On one wall of one cave, less than a century old and with an entrance about a yard wide, in the middle of an active volcano on an island isolated by thousands of miles of ocean, scientists found just the second example of a rare species of cyanobacteria.
University of Hawaii Microbiology Associate Professor Stuart Donachie was part of the team that first entered the Kilauea Caldera cave several years ago. They had enlisted a local guide to bring them to caves that hadn’t had too many human visitors. Donachie was looking to see which bacteria were present in the caves as part of his research on bacteria growing on volcanic rock surfaces.
“We went into about 20 caves in one day,” Donachie said of that initial trip. “(The guide) said he knew of one with purple stuff on the wall.”
Donachie hadn’t seen any purple growth in any of the other caves, so he followed the guide to the next lava tube, with an entrance so small it masked the larger cave below.
“It had this dark, dark green and purple biofilm” growing on the wall, he said.
Analysis of the cultures revealed a species in the Gloeobacter genus. It was just the second member of the genus to be identified. The first was found 40 years ago. In the intervening decades, cyanobacteria specialists have been on the lookout for more examples, to no avail, Donachie said.
“That’s amazing,” he said. “To find something so significant as this one blew me away.”
Scientists had trouble culturing the bacteria, though. In 2009, the National Parks Service gave Donachie special permission to collect, one last time, a fresh sample from the cave, which was located within the area of the park now closed because of the ongoing crater eruption.
Then-graduate student Jimmy Saw had “purple fingers” and was able to culture that last sample, Donachi said. Samples of Gloeobacter kilaueensis have been shared with national and international culture collections, and are being kept for the university’s use.
While the lone Kilauea cave is unlikely to be the only place the bacteria is growing, it is the only place it has been found so far. Donachie said if an eruption were to overflow the cave, the species could be lost.
“Scientifically, we’ve averted the loss of this species,” he said. “I’m hoping, in a way, we’ve saved it from extinction. We feel good about that.”
The discovery leaves several questions for scientists to consider, including where it has been growing in the 100 million years since it split from the other Gloeobacter species into its own species.
“We just don’t know how it got there,” Donachie said. “The cave is less than 100 years old. Almost no one has been in there. The sad thing is, though, we can’t go back to this cave because of the eruption.”
Cyanobacteria can be recognized for causing green slime on rocks and in streams. They are photosynthetic, using light to grow and produce oxygen. Of the 7,500 cyanobacteria, the vast majority — all but the two species of Gloeobacter — use a special membrane for photosynthesis. The lack of that membrane is what initially set apart the first Gloeobacter species, Donachie said.
The two species also have one other distinctive characteristic that doesn’t require an electron microscope to see.
“They’re both purple,” Donachie said.