Chapter 5 - Oxidative stress and the early coevolution of life and biospheric oxygen

Abstract

Reactive oxygen species (ROS) present the ultimate paradox in life and evolution, as they present both challenges and opportunities. It is likely that a rise in atmospheric O2 in the late Proterozoic supported the respiration requirements of animals. Enzymatic reduction of O2 yielded a severalfold increase in energy production perhaps triggering their first appearances or at least the development of complex ecologies that included mobility, large body plans, predation, and sediment burrowing. However, utilization of O2 also presented major challenges, as O2 and ROS are highly toxic, possibly impeding multicellular evolution after the Great Oxidation Event. Increasing evidence suggests that the ability to detoxify ROS was not a trait that emerged as a response to increased O2 levels but rather was a crucial adaptation to the early Earth’s weakly oxic microenvironments. Molecular analysis of the intrinsic regulatory systems for cellular homeostasis and redox biology shows that these pathways have been preserved throughout time, and subsequent adaptations coincided with changes in atmospheric O2 levels.