Norris, N. | Search bioRxiv

bioRxiv2021

The Induction of Pyrenoid Synthesis by Hyperoxia and its Implications for the Natural Diversity of Photosynthetic Responses in Chlamydomonas

In algae, it is well established that the pyrenoid, a component of the carbon-concentrating mechanism (CCM), is essential for efficient photosynthesis at low CO2. However, the signal that triggers the formation of the pyrenoid has remained elusive. Here, we show that, in Chlamydomonas reinhardtii, the pyrenoid is strongly induced by hyperoxia, even at high CO2 or bicarbonate levels. These results suggest that the pyrenoid can be induced by a common product of photosynthesis specific to low CO2 or hyperoxia. Consistent with this view, the photorespiratory by-product, H2O2, induced the pyrenoid, suggesting that it acts as a signal. Finally, we show evidence for linkages between genetic variations in hyperoxia tolerance, H2O2 signaling, and pyrenoid morphologies.

plant biology↗

bioRxiv2020

Mechanistic model of nutrient uptake explains dichotomy between marine oligotrophic and copiotrophic bacteria

Marine heterotrophic bacteria use a spectrum of nutrient uptake strategies, from that of copiotrophs--which dominate in nutrient-rich environments--to that of oligotrophs--which dominate in nutrient-poor environments. While copiotrophs possess numerous phosphotransferase systems (PTS), oligotrophs lack PTS and rely on ATP-binding cassette (ABC) transporters, which use binding proteins. Here we present a molecular-level model that explains the dichotomy between oligotrophs and copiotrophs as the consequence of trade-offs between PTS and ABC transport. When we approximate ABC transport in Michaelis-Menten form, we find, contrary to the canonical formulation, that its half-saturation concentration KM is not a constant but instead a function of binding protein abundance. Thus, oligotrophs can attain nanomolar KM values using binding proteins with micromolar dissociation constants and while closely matching transport and metabolic capacities. However, this requires large periplasms and high abundances of binding proteins, whose slow diffusion limits uptake rate. We conclude that the use of binding proteins is critical for oligotrophic survival yet severely constrains maximal growth rates, thus fundamentally shaping the divergent evolution of oligotrophs and copiotrophs.

microbiology↗