MICROBE 2018 recap - Astrobiology: Linking phylogeny, physiology and the rock record

Alright...admittedly the full title of this one was a bit scary for me as the only words, or more accurately, word, I really felt I had a grasp on was 'phylogeny' - yes that was it, 17 words in this title and I was like "I know what a phylogeny is":

Energy controlled distribution of isotopes in biocatalytic systems: A means of linking phylogeny, physiology and the rock record.

But I powered through.

Shawn McGlynn is from the Tokyo Institute of Technology, Earth-Life Science Institute (ESLI) his research interests include - microbial interactions, metalloproteins, early life and it's emergence, stable isotope techniques and microbial ecology. 

To learn more about his research and love of of Japanese hot springs check out his Research Story: Bridging disciplines and continents and check out his google scholar profile.

So we start with the question of:

"How do we elucidate the history of biological catalysis with the material record (sulfur isotopes)?"

So the focus is on sulfur...lets unpack some definitions, yes even those of us with PhDs have to double check ourselves and unpack words in fields we are less familiar with:

Biological Catalysis

• So in googling this I came across what appeared to be the perfect article to explain biological catalysis - "Focus on biological catalysis" - see it's right there in the title of this issue, alas it's paywalled! So if you have access to Nature Chemical Biology, check it out - there are several articles that might be of interest in this issue.
• Basically, enzymes (protein molecules) that speed up chemical reactions in cells are biological catalysts. They can speed up respiration, photosynthesis, the construction of new proteins, digestion, replication...etc. 
• So what's the difference between a chemical and biological catalyst? There is a good 2014 article in Scientific American which breaks it down nicely. "Speeding up reactions: biological vs. chemical catalysts".

"A catalyst is any substance that speeds up a reaction without taking part in it so at the end of the reaction you have the same amount of catalyst as you started with."

• Industrial catalysts (chemical) are typically metals - which have lots of electrons which they 'lend' in reactions and take back the reaction is complete. (Example = Nickel catalysts for making saturated fats).
• Biological catalysts as I stated above are enzymes, complex molecular with 'pockets' to fit 'reactants' - again the Scientific American article breaks this down nicely. SE Gould (twitter handle @labratting wrote the article so kudos to her!).

Back to the session at hand...

Material record - this is the archaeological record, material remains of the past...the rocks the fossils.

So basically we are looking for signatures of catalytic activities of enzymes (which are biological) specifically pertaining to sulfur reactions in the rocks - then we want to relate that to what we know about phylogeny. Anotherwards, how do we correlate sequence evolution with sulfur isotopic signatures in the rock record?

We find out over the course of the talk that:

• We can use kinetic isotopic fractionation for sulfur and a model relating energy and reaction rate to calculate chemical potential then relate it back to actual isotope fractionation. This was done by Wing and Halevy for Desulfovibrio vulgaris - published in 2014.
• When you have large fractionations, cell growth is slow
• When you have smaller fractionations, cells grow quickly (consuming of sulfate)

Aside - it's an older article but it nicely talks about fractionation in light of the Great Oxidation Event and has a section on sulfur fractionation and some nice figures:

Sessions et al., 2009. The continuing puzzle of the Great Oxidation Event. Current Biology.

Another interesting articles mentioning sulfur and the GOE:

Blaustein - The Great Oxidation Event:

"...sulfur isotopes, [have] an irreversible aggregation of oxygen in the atmosphere. [Research by] Farquhar and colleagues illustrated that sulfur isotopes in Earth's early atmosphere fractionate in a dependable way but when oxygen is present [rise of the cyanos!] there is consequently an ozone layer, the fractionation disappears because the ozone blocks UV rays...2.3 to 2.4 billion years ago sulfur fractionation just turned off..."

The talk was challenging for me to follow with many biochemical equations and I did not catch the specific link to phylogeny but it was interesting and I agree that:

The evolution of sulfate reduction was an energetic breakthrough.