Biology subjects

Ulrich, N. J.

Publications and source records attributed to Ulrich, N. J..

3 recordsLinked to original sources

bioRxiv2026

Multiple routes to red-shifted chlorophyll d-based photosynthesis

Strains of the cyanobacterium Acaryochloris marina exhibit diverse far-red light-harvesting properties during chlorophyll d-based photosynthesis. Here, we show that differences in light absorption among A. marina strains arise exclusively from Photosystem I (PSI) and reflect variation in multiple low-energy chlorophyll states. Time-resolved fluorescence reveals different combinations of low-energy states among strains, generating a continuum of spectral phenotypes. Cryo-EM structures of PSI at [~]1.8 [A] resolution reveal similar low-energy states arising from distinct pigment environments, demonstrating that red-shifted absorption is not governed by a single conserved motif. Phylogenetic analyses show that spectral tuning evolved through modular variation and reassortment of PSI components. These results indicate that distinct pigment configurations can converge on similar low-energy states, extending light harvesting near the energetic limit of oxygenic photosynthesis.

biophysics↗

bioRxiv2024

Niche partitioning in a cyanobacterium through divergence of its novel chlorophyll d-based light-harvesting system

The evolution of novel traits can have important consequences for biological diversification. New ecological opportunities provided by a novel trait can trigger subsequent trait modification or niche partitioning; however, the underlying mechanisms of novel trait diversification are still poorly understood. Here, we report that the innovation of a new chlorophyll (Chl) pigment, Chl d, by the cyanobacterium Acaryochloris marina was followed by the functional divergence of its light-harvesting complex. We identified three major photosynthetic spectral types based on Chl fluorescence properties for A. marina laboratory strains, with shorter and longer wavelength types more recently derived from an ancestral intermediate phenotype. Members of the different spectral types exhibited extensive variation in the Chl-binding proteins as well as the Chl energy levels of their photosynthetic complexes. This spectral type divergence is associated with differences in the wavelength dependence of both growth rate and photosynthetic oxygen evolution. We conclude that the divergence of the light-harvesting apparatus has consequently impacted A. marina ecological diversification through specialization on different far-red photons for photosynthesis.

evolutionary biology↗

bioRxiv2020

Bacterial adaptation by a transposition burst of an invading IS element

The impact of transposable elements on host fitness range from highly deleterious to beneficial, but their general importance for adaptive evolution remains debated. Here, we investigated whether IS elements are a major source of beneficial mutations during 400 generations of laboratory evolution of the cyanobacterium Acaryochloris marina strain CCMEE 5410, which has experienced a recent or on-going IS element expansion. The dynamics of adaptive evolution were highly repeatable among eight independent experimental populations and included beneficial mutations related to exopolysaccharide production and inorganic carbon concentrating mechanisms for photosynthetic carbon fixation. Most detected mutations were IS transposition events, but, surprisingly, the majority of these involved the copy-and-paste activity of only a single copy of an unclassified element (ISAm1) that has recently invaded the genome of A. marina strain CCMEE 5410. Our study reveals that the activity of a single transposase can fuel adaptation for at least several hundred generations. Impact statementA single transposable element can fuel adaptation to a novel environment for hundreds of generations without an apparent accumulation of a deleterious mutational load.

evolutionary biology↗