New Species Of Cyanobacteria Forms Intracellular Carbonates (Page 2 of 2) in pdf

Unraveling the Precambrian Enigma

The exact timing of cyanobacteria appearance is still debated,

but there is a consensus on an age older than 2.3 billion years,

since that is approximately when O

began to appear in

the Earth’s atmosphere. Yet the oldest fossils yielding

undisputed traces of extracellularly-calcified cyanobacteria

are dated at only 750–700 million years. The huge difference

in timing between the oldest cyanobacteria and the oldest

microfossils of calcified cyanobacteria has been called the

“Precambrian Enigma.”

Interestingly, Gm. lithophora was identified by molecular

methods as a member of a deeply phylogenetically divergent

order, whichdiverged from other cyanobacterial orders several

billion years ago. Gm. lithophora suggests that ancestral

cyanobacteria living from 2.3 billion to 750 million years ago

may have formed carbonates intracellularly and not extracel-

lularly as previously thought. If ancient cyanobacteria created

internal carbonates rather than external precipitates, cells

may not have been entombed within mineral shells, and so

calcified cyanobacteria microfossils may not have formed,

explaining the Precambrian Enigma! To challenge this hypoth-

esis, there is now a crucial need to understand further how Gm.

lithophoraforms intracellular carbonates and what makes this

species different from other, modern cyanobacteria.

Ca L

-edges

C K-edge

2,3

of an unknown biological mecha-

is a representative of these

nism concentrating Sr and Ba.

ancestral cyanobacteria, this

These alkaline earth ele-

process of intracellular carbon-

ments usually have similar

ate

formation

could

help

chemical

behavior,

which

explain the gap in their fossil

Carbonate

can make them difficult to

record (read the sidebar for the

inclusions

separate. This could be useful,

full story).

for example, in isolating

Not only is Gm. lithophora

contamination after a nuclear

the first observed cyanobacteria

accident. It seems that Gm.

to form intracellular carbon-

lithophora have developed a

ates, it is also only the second

mechanism that allows them to

species of bacteria found to

Cells

separate Sr from Ca. Studying

control

mineral

formation.

it will be of interest for design-

Commonly viewed as a eucary-

ing remediation strategies for

otic ability, controlling the

280

300

320

340

360

such pollutants.

formation of mineral materials

Energy (eV)

Phylogenetic analyses place

(such as bones, teeth, and

this new species within the

shells) has only been observed

Spectromicroscopy of carbon and calcium in Gm. lithophora

deeply divergent order Gleo-

in one other bacterial system:

cultures. Top: composite image showing the distribution of Ca-rich

carbonate inclusions within the bacterial cells. The distribution of

bacterales,

branch

that

bacteria

forming

intra-

inclusions was assessed based on the spectral differences between

diverged

genetically

from

cellular magnetites, which are

the material composing the cells and the Ca-carbonate inclusions

modern cyanobacteria a long,

nanomagnets. This research

at the C K-edge and the Ca L

-edges. Bottom: XANES spectra at

long time ago. If Gm. lithophora

provides a new example.

2,3

the C K-edge and the Ca L2,3 edges of the carbonate inclusions and

the cells.

262

01/13

More ALS science highlights can be found at www-als.lbl.gov

New Species Of Cyanobacteria Forms Intracellular Carbonates Page 2

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