YSM Issue 90.4
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geology and geophysics<br />
FEATURE<br />
ΜICROBIAL DIVERSITY<br />
How environmental niches affect biological diversification<br />
►BY JIYOUNG KANG<br />
IMAGE COURTESY OF NIAID/RML<br />
►Researchers examined the diversification of microbes by<br />
studying rock formations that are millions of years old.<br />
Have you ever marveled at the diversity of life on Earth?<br />
Over the past 500 million years, the development of new<br />
environmental niches has played a huge role in the diversification<br />
of plants and animals. These macro-organisms<br />
have colonized new continents and expanded to various<br />
habitats, developing novel evolutionary adaptations that<br />
have led to radiation of species. But what about the microbes?<br />
Even though we cannot see them with our naked<br />
eye, they have evolved for a much longer period of time:<br />
the past four billion years. A team of researchers sought<br />
out a possible explanation for their diversification in ancient<br />
rocks.<br />
Led by Eva Stüeken at University of St. Andrews, the<br />
team investigated whether the diversification of microbial<br />
populations was also prompted by the expansion of<br />
environmental niches. They studied five formations in<br />
the Neoarchean lower Fortescue Group, located in Western<br />
Australia. The depositional settings possess distinct<br />
hydrogeologic properties, meaning that they differ in<br />
what elements they are made out of and whether water<br />
constantly flows in and out of the lakes. But they were all<br />
formed about three million years ago, which assures that<br />
any diversity in microbes observed by the researchers is<br />
due to the difference in habitats and not time. To assess<br />
the biological and geological properties of the formations,<br />
they gathered samples from drill cores and measured<br />
traces of different elements.<br />
This allowed the researchers to identify the type of<br />
bacteria that lived in the region. When some bacteria<br />
eat, they change the type of carbon left in the environment,<br />
while other bacteria change the type of sulfur. If<br />
researchers found more of a certain type of carbon or<br />
sulfur, then they would be fairly certain that the corresponding<br />
bacteria was once in the area.<br />
After taking these measurements, the researchers concluded<br />
that geographic and hydrologic parameters indeed<br />
impact the diversification of microbes. For example,<br />
Mt. Roe Formation is made out of basaltic rocks that<br />
can react with water to generate methane. The researchers<br />
examined the site’s carbon isotope values and inferred<br />
the presence of methanotrophs—bacteria that use<br />
methane as their main source of energy. Similarly, they<br />
found evidence of different metabolisms present in other<br />
formations with various environmental properties. This<br />
is because distinct minerals release different types of elements,<br />
which shape the biological pattern of microbial<br />
populations as the organisms evolve to utilize different<br />
nutrients.<br />
“It is a pretty new concept that environmental diversification<br />
may have triggered microbiological diversification”,<br />
Stüeken said. In fact, the implications of the research<br />
extend even to astrobiology, in the effort to find<br />
extraterrestrial life. Based on the data, it may be important<br />
to focus on planets with diverse environments. “If<br />
you have a planet that only has a big ocean and no land<br />
masses, then it would perhaps be much more difficult to<br />
develop a diverse biosphere,” Stüeken said. Since there<br />
are fewer niche spaces, there would also be fewer types<br />
of bacteria.<br />
Naturally, there were challenges that followed the study<br />
of ancient rocks. The scientists had to work with the possibility<br />
that the rocks could have been metamorphosed<br />
from the exposure to great heat and pressure over the<br />
years, potentially skewing the data. Gathering samples<br />
was also difficult, as they are quite weathered and scarce.<br />
Still, the researchers hope to further the study by analyzing<br />
older and younger rocks with a similar method<br />
by comparing marine rocks to non-marine rocks. This<br />
work opens a new window into the field and may be an<br />
important step towards acknowledging the effect of environmental<br />
diversity on biological diversity.<br />
www.yalescientific.org<br />
October 2017<br />
Yale Scientific Magazine<br />
27