A plethora of previously unknown chlamydia-related bacterial strains have been discovered in the unlikeliest places: under the Arctic seafloor sediments. The discovery raises new questions about this complex and persistent bacteria community and how it came to infect humans and other species.
Chlamydia is the most recorded STD in the United States and is caused by an infection of the bacterium Chlamydia trachomatis. Chlamydia has formed the largest proportion of all recorded STDs to the U.S. since 1994. Disease Awareness and Prevention Centers.
This bacterium and its associated relatives, known collectively as Chlamydiae, can also infect other species, allowing them to survive and reproduce. Scientists call them “compulsory intracellular parasites,” meaning they can replicate only inside a host cell. Besides humans and other animals (such as koalas), Chlamydiae feed on more complex micro-organisms than themselves, including aquatic eukaryotes such as amoeba, algae, and plankton.
Chlamydiae are known to occupy a wide variety of environments but, as new research published in Current Biology reveals, their ecological range is much more diverse than we ever thought. The new paper, led by microbiologist Thijs Ettema from Wageningen University & Research in The Netherlands, reveals that the high-pressure, low-oxygen sediments under the Arctic seafloor have a diverse population of chlamydiae.
“It was completely unexpected to discover chlamydiae in this area and of course asked the question, what were they doing on Earth there?”In a press release Jennah Dharamshi, a scholar at the Swedish University of Uppsala and the first author of the new study questioned.
The Chlamydiae’s unique position contributes to this bacterial group’s resilience and versatility, while also providing new insights into its evolution and how it came to infect macro-organisms such as humans. That said, the researchers were unable to recognize any hosts inside the marine sediment, nor were they able to grow any of the newly discovered Chlamydiae in their laboratory (it’s not easy to replicate the low-oxygen high-pressure environment in which they were found). Also it is not immediately clear how this bacteria made its way into our bodies from the deep ocean, if that is indeed the direction taken. In addition, the new paper appears to raise more questions than it answers, presenting some exciting new methods of discovering and conducting scientific research.
“Chlamydiae have undoubtedly been overlooked in several past microbial diversity surveys,” said Daniel Tamari, a report co-author and a researcher at the University of Wageningen & Research, in the press release. “This community of bacteria may play a much greater role in marine ecology than we previously thought.” According to the new paper, the previously identified Chlamydiae lineages were found to “dominate microbial communities” in deep, oxygen-deprived (anoxic) marine sediments. Such sediments were at Loki’s Fortress, a series of hydrothermal deep-sea vents situated between Norway and Greenland. The bacteria were present in sample cores clustered several miles below seafloor— an area reserved for micro-organisms (as opposed to larger animals, such as brittle stars or clams).
Sample analysis showed that Chlamydiae amounted to over 43 per cent of all bacteria found in the sediment. It probably means these microorganisms have a significant impact on the local ecosystem of this oxygen-starved climate, at such large quantities. In all, the researchers were able to classify 163 distinct Chlamydiae species, one of which was determined to be a close relative to Chlamydia trachomatis, the bacterium that is responsible for human STD.
“Finding that Chlamydia has marine sediment relatives, has given us new insights into the nature of chlamydial pathogens,” Dharamshi said.
As noted, the researchers were not in a position to identify any eukaryotic hosts in the samples, so they are not sure the species they rely on. That being said, a preliminary genetic analysis of the samples indicates that they have the requisite physiological characteristics of obligatory intracellular parasites. Hence the hosts must exist— they just need to be identified.
“We discover groups of microbes which are new to science each time we visit a different environment. It shows us how much needs to be learned,’ Ettema said.