Researchers discover how Clostridium thermocellum utilizes both CO2 and cellulose
Date: 4.11.2016
Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) made the surprise discovery that a metabolic pathway to take up CO2 exists and functions in a microorganism capable of breaking down and fermenting cellulosic biomass to produce biofuels including hydrogen and hydrocarbons.
Clostridium thermocellum is among the most efficient bacteria in directly converting cellulosic materials into hydrogen and hydrocarbons biofuels.
Most bacteria feeding upon organic carbon compounds, such as glucose or xylose, release CO2 as a waste byproduct, decreasing the maximum amount of products the microorganism can produce per carbon atom measured as carbon efficiency.
Other scientists have found the addition of a form of CO2, known as bicarbonate, into the medium containing the bacterium actually promotes the growth of C. thermocellum, yet its mechanistic details remained a puzzle. This enhanced growth implied the bacterium had the ability to use CO2 and prompted NREL researchers to investigate the phenomena enhancing the bacterium's growth.
"It took us by surprise that this microbe can recapture some of the CO2 released during growth while they consume sugars derived from cellulosic biomass," said Katherine J. Chou, a staff scientist with NREL's Photobiology group.
Using carbon isotopes coupled with mass spectrometry analysis, the researchers were able to track how CO2 enters the cell, identify the enzymes critical to CO2 uptake, and how CO2 incorporates into products thereby discovering a new metabolic route unknown to the scientific community.
Many species of bacteria have the pathway in place for CO2 uptake, but before the new research, the pathway was not associated with the role of carbon dioxide assimilation (otherwise known as CO2 fixation).
The pathway enables the bacterium to use both CO2 and organic carbons during its growth, which is counter-intuitive because it's much more common for this type of organism to use one and not the other, especially in heterotrophic microbes.
