Bacterial light-harvesting proteins share a universal core but adapt to local environments
The same light-powered engine, tuned to every habitat: a global map of a bacterial light protein
Many bacteria do not photosynthesise like plants, yet still use light. Some capture extra energy from sunlight with light-driven proteins in their cell membranes; others use light purely as a signal to sense their surroundings.
"Light is essentially free. For bacteria living where energy is scarce, even a small amount of extra energy from light can affect whether they persist or disappear," says doctoral researcher Batuhan Dogan from the University of Jyväskylä.
Dogan's dissertation used computational genomics to map how light-harvesting and light-sensing systems are distributed across bacteria. Its central part is a global survey of xanthorhodopsins, a family of light-driven proton pumps that carry a built-in pigment "antenna" to capture additional light.
"I assembled 251 distinct xanthorhodopsins from public genome databases, spanning more than fifteen habitat types from Arctic glaciers, ice cores and cryoconite to lakes, seawater, hot springs and even hospital surfaces. Across all of them the proton-pumping core is almost unchanged, while the antenna region varies systematically from one environment to another," Dogan explains.
A conserved engine with an interchangeable antenna
Predicted three-dimensional structures of all 251 proteins retained the same core scaffold; the meaningful differences were concentrated at the surface, where the protein holds its light-capturing pigment.
"It behaves like a fixed engine with an interchangeable attachment. The part that pumps protons across the membrane is conserved everywhere, while the pigment-binding surface is tuned to the pigments locally available. Cold-adapted, salt-loving and algae-associated bacteria each appear to favour different antenna chemistries," says Dogan.
The sequences resolved into seven distinct lineages, each with its own ecological signature. Bacteria collected from the very same location often belonged to different lineages, indicating that this diversity reflects evolutionary history rather than where a sample happened to be taken. The structures and their metadata were compiled into an openly accessible online xanthorhodopsin atlas.
M.Sc. Batuhan Dogan defends his doctoral dissertation "Computational Biology of Microbial Phototrophy: Genomic, Structural and Ecological Diversity of Light Harvesting and Sensing" on Thursday 25th of June at 12.00 at Agora, Auditorium 2 (Ag B105). The opponent is Associate Professor Michal Koblížek (Institute of Microbiology of the Czech Academy of Sciences, Centre Algatech, Czech Republic) and the custos is Professor Janne Ihalainen (University of Jyväskylä). The language of the event is English.
