Evolution: ancient sulfur-eating bacteria (Introduction)

by David Turell , Friday, February 08, 2019, 18:46 (2114 days ago) @ David Turell

A good explanation how studies of isotopes that have been left by early life show how they lived on energy from sulfur and other mineral sources, and not from eating each other:

https://phys.org/news/2019-02-life-earth-billion-years.html

"Microbial metabolism is recorded in billions of years of sulfur isotope ratios that agree with this study's predictions, suggesting that life flourished in the ancient oceans. Using this data, scientists can more deeply link the geochemical record with cellular states and ecology.

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" Presently, the oldest evidence of microbial life on Earth comes to us in the form of stable isotopes. The chemical elements charted on the periodic table are defined by the number of protons in their nuclei. For example, hydrogen atoms have one proton, helium atoms have two, carbon atoms contain six. In addition to protons, most atomic nuclei also contain neutrons, which are about as heavy as protons, but which don't bear an electric charge. Atoms that contain the same number of protons, but variable numbers of neutrons, are known as isotopes. While many isotopes are radioactive and thus decay into other elements, some do not undergo such reactions; these are known as "stable" isotopes. For example, the stable isotopes of carbon include carbon 12 (written as 12C for short, with 6 protons and 6 neutrons) and carbon 13 (13C, with 6 protons and 7 neutrons).

"All living things, including humans, "eat and excrete." That is to say, they take in food and expel waste. Microbes often eat simple compounds made available by the environment. For example, some are able to take in carbon dioxide (CO2) as a carbon source to build their own cells. Naturally occurring CO2 has a fairly constant ratio of 12C to 13C. However, 12CO2 is about 2 percent lighter than 13CO2, so 12CO2 molecules diffuse and react slightly faster, and thus the microbes themselves become "isotopically light," containing more 12C than 13C, and when they die and leave their remains in the fossil record, their stable isotopic signature remains, and is measurable. The isotopic composition, or "signature," of such processes can be very specific to the microbes that produce them.

"Besides carbon, there are other chemical elements essential for living things. For example, sulfur, with 16 protons, has three naturally abundant stable isotopes, 32S (with 16 neutrons), 33S (with 17 neutrons) and 34S (with 18 neutrons). Sulfur isotope patterns left behind by microbes thus record the history of biological metabolism based on sulfur-containing compounds back to around 3.5 billion years ago.

"Hundreds of previous studies have examined wide variations in ancient and contemporary sulfur isotope ratios resulting from sulfate (a naturally occurring sulfur compound bonded to four oxygen atoms) metabolism. Many microbes are able to use sulfate as a fuel, and in the process excrete sulfide, another sulfur compound (Figure 1). The sulfide "waste" of ancient microbial metabolism is then stored in the geological record, and its isotope ratios can be measured by analyzing minerals such as the FeS2 mineral pyrite.

"This new study reveals a primary biological control step in microbial sulfur metabolism, and clarifies which cellular states lead to which types of sulfur isotope fractionation. This allows scientists to link metabolism to isotopes: By knowing how metabolism changes stable isotope ratios, scientists can predict the isotopic signature organisms should leave behind.

"This study provides some of the first information regarding how robustly ancient life was metabolizing. Microbial sulfate metabolism is recorded in over 3 billion years of sulfur isotope ratios that are in line with this study's predictions, which suggest life was in fact thriving in the ancient oceans."

Comment: This is very important article as it explains how early bacteria could live on the energy in electrons from minerals. Evolving life has always needed energy intake and excretion of waste products and will leave traces. Bacteria are extremely complex creatures as they must do everything we do but within one cell. Early life couldn't find much protein to ingest fore energy , so this was required, and it is still seen today in extremeophiles.