By all scientific accounts, conditions on planet Earth were pretty inhospitable in the early days. The earliest organisms, such as extremophilic archaea, readily adapted to what we would view today as uninhabitable climates. However, as the planet evolved and slowly cooled, moderate conditions began to pop up around the globe, allowing extremophiles to move to more moderate conditions. Now, a team of researchers led by scientists at the University of Vienna, Austria, believe they have found how one type of extremophile, a heat-loving microbe that uses ammonia for energy production, may have been able to make the transition. Findings from the new study were published recently in Frontiers in Microbiology in an article entitled “Candidatus Nitrosocaldus cavascurensis, an Ammonia Oxidizing, Extremely Thermophilic Archaeon with a Highly Mobile Genome.”
This first-ever analysis of DNA for a contemporary heat-loving, ammonia-oxidizing organism reveals that evolution of the necessary adaptations may have been helped by highly mobile genetic elements and DNA exchange with a variety of other organisms.
Most extremophiles are microorganisms—and many of the most extreme are archaea, an ancient group of single-celled organisms intermediate between the other two domains of life, bacteria and eukaryotes. Different archaea lineages are specialized to different extreme environments, including scalding hot springs, incredibly salty lakes, sunless deep-sea trenches, and frigid Antarctic deserts. Only one branch, the phylum Thaumarchaeota, has managed to successfully colonize the Earth's more hospitable places—but scientists don't know why.
“Thaumarchaeota are found in very large numbers in virtually all environments, including the oceans, soils, plant leaves, and the human skin,” explained lead study investigator Christa Schleper, Ph.D., a professor at the University of Vienna. “We want to know what their secret is. Billions of years ago, how did they adapt from hot springs, where it seems all archaea evolved, to more moderate habitats?”
To find the answer to their question, the research team began by isolating a Thaumarchaeota species from a hot spring in Italy and then sequencing and analyzing its genome. This represents the first genome analysis of the Nitrosocaldus lineage—a subgroup of heat-loving Thaumarchaeota that get their energy by oxidizing ammonia into nitrite.
Interestingly, the researchers found that the organism, Candidatus Nitrosocaldus cavascurensis, seems to represent the closest-related lineage to the last common ancestor of all—Thaumarchaeota. Moreover, C. Nitrosocaldus cavascurensis seems to have highly mobile DNA elements and seems to have frequently exchanged DNA with other organisms—including other archaea, viruses, and possibly even bacteria.
Many researchers assume that the first life forms on Earth evolved in hot springs. Further studies of this thermophile archaeon might help identify general mechanisms that enabled the first living cells, both bacteria and archaea, to conquer the world.