life's forms modify, evolve the Earth: cyanobacteria origin (Introduction)

by David Turell @, Sunday, October 29, 2023, 00:28 (175 days ago) @ David Turell

So important for oxygen:

"Cyanobacteria are a key species in Earth's history, as they introduced atmospheric oxygen for the first time. The analysis of their evolution therefore provides important insights into the formation of modern aerobic ecosystems. For a long time, a certain type of fossil lipid, so-called 2-methylhopanes, was considered to be an important biomarker for Cyanobacteria in sediments, some of which are hundreds of millions of years old. However, this came into doubt when it turned out that not only Cyanobacteria but also Alphaproteobacteria are genetically capable of producing these lipids.


"Center for Marine Environmental Sciences at the University of Bremen has now studied the phylogenetic diversification and distribution of the genes -- including HpnP -- that are responsible for the synthesis of the parent lipids for 2-methylhopanes: The researchers have deciphered when these genes were acquired by certain groups of organisms. They were able to show that HpnP was probably already present in the last common ancestor of Cyanobacteria more than two billion years ago, while the gene only appeared in Alphaproteobacteria about 750 million years ago. For the times before that, 2-methylhopanes can therefore serve as a clear biomarker for oxygen-producing Cyanobacteria.


"Cyanobacteria played a crucial role in transforming the Earth from its initial oxygen-free state to a modern, oxygen-rich system in which increasingly complex life is possible. Cyanobacteria were probably the only relevant group of organisms that converted inorganic substances into organic ones (so-called primary producers) and produced oxygen for long stretches of the Precambrian (the first four billion or so years of Earth's history, from its beginnings to about 540 million years ago). [start of the Cambrian era]


"... due to preservational biases and ambiguities in recognizing fossil cyanobacterial cells, geochemists rather use fossilised diagnostic lipids, such as 2-methylhopanes. 2-Methylhopanoids (non-fossilised parent molecules) are produced by the bacteria and -- in contrast to the bacteria themselves- can be fossilised and detected in sedimentary rocks even after hundreds of millions of years in good quality and in quantities corresponding to their original occurrence.

"However, there have recently been doubts about the suitability of 2-methylhopane as a biomarker for Cyanobacteria: the discovery of the lipid biosynthesis gene revealed that Alphaproteobacteria are also capable of producing these lipids. This means that temporally tracing oxygen-producing processes on Earth by 2-methylhopanes is no longer possible.

"...University of Bremen has now systematically investigated which organisms other than Cyanobacteria possess the genes (abbreviated as the SC and HpnP genes) necessary for the production of 2-methylhopanoids, and when they acquired those genes during the course of evolution. In this way, the team was able to show that the fossil lipid 2-methylhopane can still be used as a clear biomarker for the existence of Cyanobacteria for times dating back more than 750 million years.


"There are many bacteria that possess both SC and HpnP genes, but they are mainly Cyanobacteria and Alphaproteobacteria. Each group is found to have acquired the two genes independently. This is in contrast to earlier studies that concluded that Cyanobacteria acquired these genes from Alphaproteobacteria at a late stage in their evolution. The new study further revealed that the common ancestor of Cyanobacteria already possessed both genes more than 2.4 billion years ago, when oxygen began to accumulate in the atmosphere during the so-called Great Oxidation Event. (my bold)

"In contrast, Alphaproteobacteria acquired the SC and HpnP genes at the earliest only 750 million years ago. Before that, 2-methylhopanoids were thus only produced by Cyanobacteria. The researchers interpret a slightly delayed increase of sedimentary 2-methylhopanes around 600 million years ago as a sign of the global spread of Alphaproteobacteria, which may have favored the concurrent evolutionary rise of eukaryotic algae."

Comment: Note my bold. I view the appearance of oxygen producing genes 2.4 billion years ago as a purposeful event in designing for life on Earth with preparation for the future appearance of oxygen breathing for land and ocean organisms. Noting purposeful events is the best way to analyze how God evolved us by design. Always planning for the future developments. It explains why speciation often covers the future needs.

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