Wijker, R. S. | Search bioRxiv

bioRxiv2025

Diversity in Rubisco Kinetics and CO2-Concentrating Mechanisms Among Cyanobacterial Lineages

Cyanobacteria are the most ancient oxygenic photosynthetic organisms on Earth and play a pivotal role in the global carbon cycle. Despite their ecological and evolutionary significance, the mechanisms of carbon acquisition and fixation in this phylum remain largely unexplored beyond a few model species. Here, we examined representative taxa spanning the full phylogenetic breadth of Cyanobacteria, assessing in vivo carbon-acquisition pathways, the role and efectiveness of CO2-concentrating mechanisms (CCMs), as well as conducting in vitro biochemical characterizations of the kinetic traits and carbon isotope fractionation of Rubisco. We found significant lineage-specific diferences in Rubisco kinetics and CCM performance, but a common signature of high Rubisco catalytic turnover coupled with low CO2 afinity--consistent with the co-evolution of this enzyme together with powerful CCMs. Furthermore, we identified a strong positive correlation between Rubisco carbon isotope fractionation and its CO2/O2 specificity factor. Together, these results provide fresh insight into Rubisco catalysis and shed light on its co-evolution with CCMs, underscoring their role in shaping Earths carbon dynamics.

plant biology↗

bioRxiv2025

Symbiotic entrenchment through ecological Catch-22

Symbiotic organisms frequently evolve obligate dependencies on hosts, but the evolutionary changes that entrench such lifestyles are poorly understood. Ant societies are vulnerable to parasitic "myrmecophiles": impostor species that infiltrate colonies and are often unable to survive outside of them. Here we show that obligate dependence of a myrmecophile on its host arises from irreversibility of the fundamental steps that achieve social acceptance inside the nest. We report a convergent system in which parallel rove beetle lineages (Staphylinidae) evolved from free-living ancestors to parasitize the same host ant. Exploiting this system, we uncover cellular mechanisms by which these beetles mimic host ant cuticular hydrocarbons (CHCs): nestmate recognition pheromones, which function pleiotropically to prevent desiccation. We present evidence of a biological stealth mechanism in a rove beetle in which the CHC biosynthetic machinery becomes transcriptionally silenced on entering the nest. Silencing transforms the beetle into a chemical blank slate onto which ant CHCs are horizontally transferred via interspecies grooming behavior. This strategy leads to identical chemical resemblance and seamless social integration within the colony. CHC pathway silencing is irreversible, however, forcing the beetle into a chronic, physically close dependence on ants to both maintain nestmate status and prevent desiccation. Loss of CHC silencing renders the beetle detectable to ants; conversely, loss of behavioral attraction to ants renders the beetle desiccation prone. Our findings show how symbiotic entrenchment can arise from a Catch-22-like ratchet operating at the organismal level.

evolutionary biology↗