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Metabolic evolution and the self-organization of ecosystems
#MMPMID28348231
Braakman R
; Follows MJ
; Chisholm SW
Proc Natl Acad Sci U S A
2017[Apr]; 114
(15
): E3091-E3100
PMID28348231
show ga
Metabolism mediates the flow of matter and energy through the biosphere. We
examined how metabolic evolution shapes ecosystems by reconstructing it in the
globally abundant oceanic phytoplankter Prochlorococcus To understand what drove
observed evolutionary patterns, we interpreted them in the context of its
population dynamics, growth rate, and light adaptation, and the size and
macromolecular and elemental composition of cells. This multilevel view suggests
that, over the course of evolution, there was a steady increase in
Prochlorococcus' metabolic rate and excretion of organic carbon. We derived a
mathematical framework that suggests these adaptations lower the minimal
subsistence nutrient concentration of cells, which results in a drawdown of
nutrients in oceanic surface waters. This, in turn, increases total ecosystem
biomass and promotes the coevolution of all cells in the ecosystem. Additional
reconstructions suggest that Prochlorococcus and the dominant cooccurring
heterotrophic bacterium SAR11 form a coevolved mutualism that maximizes their
collective metabolic rate by recycling organic carbon through complementary
excretion and uptake pathways. Moreover, the metabolic codependencies of
Prochlorococcus and SAR11 are highly similar to those of chloroplasts and
mitochondria within plant cells. These observations lead us to propose a general
theory relating metabolic evolution to the self-amplification and
self-organization of the biosphere. We discuss the implications of this framework
for the evolution of Earth's biogeochemical cycles and the rise of atmospheric
oxygen.
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