thescientist | The tree of life is dominated by microbes, but many large branches
remain uncharted because scientists have been historically restricted to
studying the small fraction of species that will grow in a lab. An
international team of scientists has now begun to redress this bias,
sequencing full genomes from single cells to bring the “uncultured
majority” into view.
In total, the team identified more than 200 new microbial species
belonging to 29 underrepresented or unknown lineages. And the results,
published today (July 14) in Nature, were full of new metabolic abilities and genetic surprises.
“[There has been a] strong imperative to fill in the microbial tree of
life,” said Philip Hugenholtz from the University of Queensland, one of
the study’s leaders. “If you have an incomplete view of evolution—vastly
incomplete in the case of microorganisms—you have a vastly incomplete
understanding of biology.”
By sequencing DNA directly from environmental samples, geneticists have
suggested that the two microbial domains of life—bacteria and
archaea—include at least 60 major lineages (phyla), but just four of
these account for more than 88 percent of cultivated microbes. Of the
others, around half are “candidate phyla,” whose members have never been
grown in lab cultures.
To fill these gaps, the team collected samples from nine diverse
habitats, including industrial reactors, hot springs, and a gold mine.
The researchers gravitated towards places that were low in oxygen since
these tend to harbor a greater and more interesting spread of microbes
than familiar sites like our bodies.
From these samples, Tanja Woyke from the Department of Energy’s Joint
Genome Institute in California isolated 9,600 individual cells and
amplified the genomes of around a third of these. If any of these
genomes looked like they came from new lineages, the team sequenced them
completely.
They ended up with 201 full genomes representing 21 bacterial lineages
and 8 archaeal ones. Some of these were candidate phyla known only by
abstract codes, but the team has now given them descriptive names based
on the biology of their members. For example, EM19 is now Calescamantes
(“heat lovers”) because they hail from an extremely hot environment, and
OD1 is now Parcubacteria (“thrifty bacteria”) for its streamlined
metabolism.
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