EVOLUTION, ADAPTIVE STRESSORS AND MOLECULAR HYDROGEN

Molecular hydrogen (H2) has demonstrated therapeutic properties across numerous models. To date, the mechanism underlying the beneficial responses toH2 exposure remains elusive. The initial hypothesis that molecular hydrogen acts as a direct, selective antioxidant in vivodoes not reconcile models where H2 has shown to increase oxidative stress, nor does it explain numerous other physiological changes that have been observed throughout the literature. Some researchers have proposed that H2acts as ahormetic stress. This hypothesisdoes not reconcile H2 being non-toxic in nature, even at high doses. Hormeticstressors have contributedto evolutionary adaptations, with the absence of these stressors causing cellular dysfunction.H2 has played an intimate role in the evolution of our planets atmosphere, the evolution of mitochondria andof life on the planet.Endogenously produced H2 volumes vary dramatically between individuals and are expected to have varied through human evolution.Our cells have evolved to tolerate erratic and intermittent exposure to H2. Intermittent exogenous H2exposure yields results similar to various hormetic stressors. Continued research elucidating how H2 acts as an adaptive stressor, both through endogenous levels and exogenous supplementation, are highly warranted.

Engineering yeast endosymbionts as a step toward the evolution of mitochondria

It has been hypothesized that mitochondria evolved from a bacterial ancestor that initially became established in an archaeal host cell as an endosymbiont. Here we model this first stage of mitochondrial evolution by engineering endosymbiosis betweenEscherichia coliandSaccharomyces cerevisiae. An ADP/ATP translocase-expressingE. coliprovided ATP to a respiration-deficientcox2yeast mutant and enabled growth of a yeast–E. colichimera on a nonfermentable carbon source. In a reciprocal fashion, yeast provided thiamin to an endosymbioticE. colithiamin auxotroph. Expression of several SNARE-like proteins inE. coliwas also required, likely to block lysosomal degradation of intracellular bacteria. This chimeric system was stable for more than 40 doublings, and GFP-expressingE. coliendosymbionts could be observed in the yeast by fluorescence microscopy and X-ray tomography. This readily manipulated system should allow experimental delineation of host–endosymbiont adaptations that occurred during evolution of the current, highly reduced mitochondrial genome.

Mitochondrial clock: moderating evolution of early eukaryotes in light of the Proterozoic oceans

Evolution of early eukaryotes in the primitive Earth relied heavily on the origin and evolution of mitochondria. Understanding the structure and origin of mitochondria has a germane relation to understanding origin and evolution of eukaryotes. In light of the extreme conditions and the then existing Proterozoic ocean chemistry, eukaryotic cells developed adaptive adjustments for energy management. Apart from mitochondria, more reduced homologues like hydrogenosomes and mitosomes facilitated the metabolic activities of such eukaryotic life. In this short review, I highlight the importance of mitochondria in pushing eukaryotes to the peak of the evolutionary pyramid. Our knowledge has expanded but studying recent eukaryotic extremophiles and mitochondrial genomics in more details will enable us to estimate the position of the mitochondrial clock, understand its role better, and possibly find new eukaryotic lineages.