The mystery microbes making rock in a Chilean lake
Analysis of an extremophile habitat reveals a surprising absence, and throws up many questions. Andrew Masterson reports.
Unknown microbes with unknown metabolisms may be living in one of the world’s harshest environments – an area in Chile so tough that even cyanobacteria, the almost ubiquitous phylum that includes blue-green algae, struggle to survive.
Discovering these as yet unidentified microbes, and revealing how they function, could provide valuable insight into how life developed on the early Earth, according to a paper published in the journal PLOS ONE.
A team of scientists, led by microbiologist Maria Eugenia Farias of the Laboratorio de Investigaciones Microbiologicas de Lagunas Andinas in Argentina, set out to examine the microbial diversity found in Laguna La Brava, a lake in Chile’s Salar de Atacama salt flat.
The lake is extreme even by the standards of extremophiles: it is characterised by hyper-salinity, high levels of solar radiation, and the water itself contains significant amounts of metals, including lithium, arsenic, magnesium and calcium. It is one of the most unfriendly environments on the planet.
Farias and her colleagues examined the primitive unicellular communities that exist at various depths in the lake. They are all described as “geomicrobiological” entities: collections of species that either gradually trap or create sediments to form layers or microbial mats, known collectively as microbialites – structures that include three-billion-year-old species that build stromatolites, similar to those found at Shark Bay in Western Australia, or, recently, in a freshwater system in Tasmania.
There was one very significant difference, however. Analysis of the Tasmanian stromatolites found that the microbial community was dominated by cyanobacteria.
The Laguna La Brava microbialites, however, contained several other types of bacteria and archaeans – including the families Euryarchaeota, Crenarchaeota, Acetothermia, Firmicutes and Planctomycetes – but cyanobacteria accounted for less than 4% of organisms in some structures and was undetectable in others.
This was unexpected, because cyanobacteria are known to be important catalysts in the mineralisation of microbial mats.
Their absence leads to the suggestion that other lifeforms – identity and inner workings currently unknown – are playing roles in creating the living rock carbonate that characterises much of the biological matter in the lake.
“These systems may contain previously uncharacterised community metabolisms, some of which may be contributing to net mineral precipitation,” the scientists conclude.
“Further work on these sites might reveal novel organisms and metabolisms of biotechnological interest.”