Few Anaerobic Bacteria Uses Reverse TCA Cycle to Survive in a Hydrothermal Environment

CO 2 appears to most microbes as a feast rather than a hazard. Microbes have CO 2 -fixation pathways at their disposal, which enable them to integrate CO 2 into their cell mass. Hippea maritima ,  an anaerobic bacteria that grow at high temperatures (~60°C) and CO 2 concentrations (up to 40%, 1,000 times higher than ambient CO 2 levels), uses the reverse oxidative tricarboxylic acid (TCA) cycle to survive in a hydrothermal environment such as hot springs. H. maritima, when fed with amino acids and CO 2 labeled with the 13 C isotope of carbon, channeled these food sources into the reversed oxidative TCA cycle.

This helped determine the carbon source and the pathway used by H. maritima to drive the TCA cycle backward. The reverse TCA cycle might be functional in autotrophic CO 2 fixation on a primordial earth that was rich in CO 2. Which enzyme enables the TCA cycle to run backward in…