News

By Natalia Bateman, CoETP, February 26, 2017

Take a breath. New research has found that the tiny bacteria responsible for transforming Earth three billion years ago into the oxygen-rich atmosphere you are breathing, are able to adapt to extreme levels of oxygen by having different genetic responses.

“We investigated an ancient marine bacteria, called Acaryochloris marina, which is found in extremely inhospitable habitats with very low or high levels of oxygen, where other organisms would be unable to survive.  This remarkable bacteria, lives under other organisms so they don’t get much light to produce their own food, a problem they have solved by capturing sunlight using a different type of chlorophyll,” said lead researcher Dr Miguel Hernandez, from the ARC Centre of Excellence for Translational Photosynthesis.

CoETP Dr Miguel Hernandez exploring A. Marina genome.

Before photosynthesis occurred for the first time in this planet – around 3.5-2.4 billion years ago – it was simply impossible for organisms like humans, fish or birds to survive on it. One of the reasons was that the levels of oxygen in the atmosphere were extremely low. This all changed when photosynthetic organisms, like A. marina, increased the levels of oxygen to over 21%.

“Our ultimate goal is to find the gene or genes responsible of the production of chlorophyll d, the molecule responsible for capturing sunlight on these bacteria. We knew that these genes respond to extreme levels of oxygen, so we created a road map of all the genetic responses to oxygen, and we think we have found some potential chlorophyll genes,” Dr Hernandez said.

To learn more about how A. marina adapted to extreme environments, the team grew A marina at different levels of oxygen, from very low (less than 0.2 %) to very high (65-75%).

The results concluded that the level of oxygen triggers different genetic regulatory responses in A marina depending on the oxygen concentration in its environment.

Creating extreme oxygen environments for A. Marina in the lab

“A. marina has the largest genome of the cyanobacteria and it is unknown why they have so many copies of their genes. This study reveals that part of the reason is that they need to have flexible genetic responses to extreme oxygen levels,” said Professor Min Chen, a Chief Investigator from the ARC Centre of Excellence for Translational Photosynthesis.

“We found that A. marina genome has many non-coding RNA, that is, bits of genes that don’t produce proteins directly, but usually help to regulate the production of proteins. The interesting thing is that in this case many of them are related to oxygen level regulation”, she said.

This study is also the first experiment to grow cyanobacteria in high levels of oxygen.

“Previously scientists assumed that high levels of oxygen were bad for cyanobacteria, as chlorophyll reacts dramatically with oxygen under light. Unexpectedly, our experiment shows that the genetic response to high oxygen levels is not as strong as the response to low oxygen,” Professor Chen said.

Finding out how these bacteria adapt to different oxygen levels will shed light on the evolution and regulation of photosynthesis. Scientists could potentially utilise this information to improve photosynthesis and increase the production of biofuels and food crops.

This study was published recently in the journal G3: Genes, genomes, genetics and was funded by the Australian Research Council (ARC).