Bacteria
go extinct at substantial rates, although appear to avoid the mass extinctions
that have hit larger forms of life on Earth
Bacteria
go extinct at substantial rates, although appear to avoid the mass extinctions
that have hit larger forms of life on Earth, according to new research from the
University of British Columbia (UBC), Caltech, and Lawrence Berkeley National
Laboratory. The finding contradicts widely held scientific thinking that
microbe taxa, because of their very large populations, rarely die off.
The study,
published today in Nature Ecology
and Evolution, used massive
DNA sequencing and big data analysis to create the first evolutionary tree
encompassing a large fraction of Earth's bacteria over the past billion years.
"Bacteria
rarely fossilize, so we know very little about how the microbial landscape has
evolved over time," says Stilianos Louca, a researcher with UBC's
Biodiversity Research Centre who led the study. "Sequencing and math
helped us fill in the bacterial family tree, map how they've diversified over
time, and uncover their extinctions."
Louca and
colleagues estimate between 1.4 and 1.9 million bacterial lineages exist on
Earth today. They were also able to determine how that number has changed over
the last billion years—with 45,000 to 95,000 extinctions in the last million
years alone.
"While
modern bacterial diversity is undoubtedly high, it's only a tiny snapshot of
the diversity that evolution has generated over Earth's history," says Louca.
Despite
the frequent, steady extinction of individual species, the work shows
that—overall—bacteria have been diversifying exponentially without
interruption. And they've avoided the abrupt, planet-wide mass extinctions that
have periodically occurred among plants and animals. Louca suspects that
competition between bacterial species drive the high rate of microbial
extinctions, leaving them less prone to sudden mass, multi-species extinctions.
Past
speciation and extinction events leave a complex trace in
phylogenies—mathematical structures that encode the evolutionary relatedness
between existing bacterial species.
"This
study wouldn't have been possible 10 years ago," says Michael Doebeli, UBC
mathematician and zoologist, and senior author on the paper. "Today's
availability of massive sequencing data and powerful computational resources
allowed us to perform the complex mathematical analysis."
Next,
Louca and his colleagues want to determine how the physiological properties of
bacteria evolve over time, and whether their ecological diversity has also been
increasing similarly to their taxonomic diversity. If this is true, it would
mean that even ancient and relatively simple organisms such as bacteria still
have the potential to discover novel ways to survive.
Posted by Dr. Tim Sandle,
Pharmaceutical Microbiology