Scientific American - November 2018

November 2018, ScientificAmerican.com 35

Methane

2CH 4

ANME

8 electrons

Sulfate

2(SO 4 )2-

SRB

Ÿåù ̈Šmy

Bicarbonate 2HS-

2HCO 3 - Waterer

2 2HH 2 OO

WWatWatteer

HH 22 OO

CaCaCalciucium

Ca2+

Calcium

carbonate

CaCO 3

Cararbobonbonb

mŸmŸ¹Ÿ¹Ÿ¹āŸmāŸmmyyy

COOO 22

3ù ̈Šmy

2H 2 S

ĂmĂmà¹ā๟my

2 2OH2OH2OH--

'āĂ'āĂ'āĂ'āÑy‘y ́‘y ́‘y ́

4 4O 22

Ăm๑y ́Ÿ¹ ́ ́ ́ ́åååå

4H4H+

Sulfate

2(SO 4 )2-

ANME/SRB clumps

Methane

CH 4

3ymŸ®y ́ï

Microbial mat

Rock

Noot tosscccaleaa

Illustration by Tami Tolpa

SOURCES: “A MARINE MICROBIAL CONSORTIUM APPARENTLY MEDIATI

NG ANAEROBIC OXIDATION OF METHANE,” BY ANTJE BOETIUS ET AL., IN

NATURE,

VOL. 407; OCTOBER 5, 2000; “SINGLE CELL ACTIVITY REVEALS DIRECT ELECT

RON TRANSFER IN METHANOTROPHIC

CONSORTIA,” BY SHAWN E. MCGLYNN ET AL., IN

NATURE,

VOL. 526; OCTOBER 22, 2015; “METHANE-DERIVED CARBONATES AND AUTH

IGENIC PYRITE FROM THE NORTHWESTERN BLACK SEA,” BY J. PECKMANN ET

AL., IN

MARINE GEOLOGY,

VOL. 177, NOS. 1–2; JUNE 30, 2001

these species, as well as how cells and biomolecules work in

general. When researchers then zoomed out from these studies

to understand the biosphere as a whole, stitched together from

the constituent species, however, major gaps in their knowledge

remained. Only a tiny fraction of microbes seen in the wild could

be isolated, suggesting that the species making up complex natu-

ral communities are intertwined in ways that cannot easily be

replicated in the laboratory. And the very coexistence of many

thriving species, which often play complementary roles, seemed

to contradict the conventional wisdom that microbial eco-

systems revolve around a winner-take-all struggle for resources.

Moreover, metabolic activity rates of individual species

measured in the lab—such as how quickly they produce oxygen

or consume nitrogen—rarely matched values from real-world

environments because species that can be isolated in the lab are

often more vigorous than those that cannot be. In other words,

the whole was sometimes more, sometimes less, but always

different from the sum of the parts.

But a growing body of evidence suggests that these discon-

nects can be reconciled by considering the vital importance of

interactions among organisms. Over the past decade advances in

bio molecular sequencing and microscopic imaging, among other

technologies, have en abled researchers to study microbial com-

munities more holistically than ever before. The latest findings

indicate that collaboration is a critical driver of the biosphere: as

individual organisms evolve to share energy, genetic information

and metabolic duties, they unlock new ways of life and gain entry

to previously inaccessible habitats.

The Mystery of the

Missing Molecules

In layers of sediment and rock under the sea-

‹ ̧ ̧ßj­xîšD³xD³läø§…Dîx­ ̧§x`ø§xäl ̧DþD³-

žäšž³D`îÍ3`žx³îžäîä§ ̧³äøäÇx`îxlD­ž`ß ̧Ux

ÿDäßxäÇ ̧³äžU§x… ̧ßîšxžßlžäDÇÇxDßD³`xjUøî

îšxā` ̧ø§l³ ̧lD³ž³lžþžløD§äÇx`žxä`DÇDU§x

̧…` ̧³äø­ž³U ̧îš­ ̧§x`ø§xäÍþx³îøD§§āîšxā

ßxD§žąxl³ ̧î ̧³xUøîîÿ ̧îāÇxä ̧…­ž`ß ̧Uxäj

ÿ ̧ߦž³î ̧xîšxßjÿxßxî ̧U§D­xÍ

A Classic Symbiosis

Methane molecules are rich in energy, but their

chemical stability makes it tough to access their

energy. Anaerobic methanotrophs (ANME) can

crack these molecules open, but the electrons

that are released ● 1 can accumulate, slowing

metabolism. Luckily for the methanotrophs,

nearby sulfate-reducing bacteria (SRB) take up

the excess electrons ● 2 , using them to convert

åù ̈†DïyŸ ́ï¹åù ̈Šmy● 3 and harvesting the resulting

energy. Ultimately much of the methane-derived

carbon precipitates as calcium carbonate rock ● 4 ,

building large mounds at methane seeps.

1 2

3

4