Resurrected Rubisco suggests uniform carbon isotope signatures over geologic time

The earliest geochemical indicators of microbes—and the enzymes that powered them—extend back ∼3.8 Ga on Earth. Paleobiologists often attempt to understand these indicators by assuming that the behaviors of extant microbes and enzymes are uniform with those of their predecessors. This consistency in behavior seems at odds with our understanding of the inherent variability of living systems. Here, we examine whether a uniformitarian assumption for an enzyme thought to generate carbon isotope indicators of biological activity, RuBisCO, can be corroborated by independently studying the history of changes recorded within RuBisCO’s genetic sequences. We resurrected a Precambrian-age RuBisCO by engineering its ancient DNA inside a cyanobacterium genome and measured the engineered organism’s fitness and carbon-isotope-discrimination profile. Results indicate that Precambrian uniformitarian assumptions may be warranted but with important caveats. Experimental studies illuminating early innovations are crucial to explore the molecular foundations of life’s earliest traces. [Display omitted] •Precambrian-age, ancestral RuBisCO gene resurrected in modern cyanobacteria•Ancient RuBisCO decreases fitness of cyanobacterial host•C-isotope signatures of cyanobacteria with ancient RuBisCO fall within modern range•Molecular paleobiology tests assumptions regarding paleogeochemistry interpretations Kędzior et al. reconstruct a Precambrian-age, ancient RuBisCO by engineering its inferred ancestral DNA inside a modern cyanobacterium genome, linking paleogeochemistry and evolutionary biology. Further inquiries are needed to discern whether enzyme-affected isotope fractionation trends extend deeper into the early Precambrian.