Biology subjects

Osmers, P.

Publications and source records attributed to Osmers, P..

3 recordsLinked to original sources

bioRxiv2026

Temperature stress resilience in polar Chlamydomonas is regulated by acclimation to light and salinity: implications for survival in a changing world

O_LIAquatic algae are key primary producers in the Arctic and Antarctic, yet how cold-water species respond to environmental change is poorly understood. The Polar Regions are increasingly exposed to frequent heat waves, leading to declining ice cover, increased light availability, and decreasing salinity in polar waters. We compared three phylogenetically related but geographically distant polar Chlamydomonas species to test how habitat history shapes algal responses to light, salinity, and temperature stress. C_LIO_LIWe assessed the growth, morphology, and photochemistry of psychrophilic Chlamydomonas acclimated to native-like (lower light, higher salinity) and climate-shifted conditions (higher light, lower salinity). Next, we exposed acclimated cultures to a lethal heat shock and observed how acclimation affects algal temperature stress resilience. C_LIO_LIAll three species acclimated to climate-shifted conditions grew rapidly but showed the greatest sensitivity to temperature stress, with rapid loss of viability and photosynthetic efficiency. In contrast, slow-growing cultures acclimated to native-like conditions exhibited significantly greater resilience to temperature stress. C_LIO_LIOur work is the first to directly link light and salinity acclimation with temperature resilience in psychrophilic algae, suggesting that fast-growing polar green algae may be particularly vulnerable to increasingly frequent heat waves, with major implications for primary productivity in polar environments. C_LI

plant biology↗

bioRxiv2025

A Suite of Stains: Characterization of four fluorophores as complementary tools for visualizing neutral lipids in an extremophilic green alga

Understanding lipid metabolism in algae is critical to advancing our knowledge on fundamental algal physiology and for harnessing these organisms as platforms for the sustainable production of high-energy lipids. BODIPY is the most prevalently used fluorescent dye for the visualization of lipid droplets (LDs) in algae; however, its limitations warrant exploration of alternatives. Here we evaluate and compare four lipophilic fluorophores (BODIPY, DAF, Cou, DPAS) for their effectiveness in staining LDs in the extremophilic green alga Chlamydomonas priscui. We assess each dyes photophysical properties, synthetic accessibility, LD specificity, cellular toxicity, and suitability for microscopy and flow cytometry. All four dyes successfully stain LDs, but their performance diverges under different experimental conditions. BODIPY permits long-term incubation allowing quantification in time-course studies but exhibits poor LD specificity and high susceptibility to photobleaching. DAF enables polarity-sensitive staining but is highly toxic on prolonged exposure or during cellular stress. Cou and DPAS yield strong LD-specific signals with low cytotoxicity, making them ideal for studies involving environmental stress. However, DPAS requires room-temperature incubation, pointing toward greater potential utility for non-extremophilic algae. These results expand the toolbox for lipid biotechnology research in extremophiles and underscore the importance of tailoring dye selection and experimental conditions to algal physiology.

plant biology↗

bioRxiv2023

Aberrant light sensing and motility in the green alga Chlamydomonas priscuii from the ice-covered Antarctic Lake Bonney

The Antarctic green alga Chlamydomonas priscuii is an obligate psychrophile and an emerging model for photosynthetic adaptation to extreme conditions. Endemic to the ice-covered Lake Bonney, this alga thrives at highly unusual light conditions characterized by very low light irradiance (<15 mol m-2 s-1), a narrow wavelength spectrum enriched in blue light, and an extreme photoperiod. Genome sequencing of C. priscuii exposed an unusually large genome, with hundreds of highly similar gene duplicates and expanded gene families, some of which could be aiding its survival in extreme conditions. In contrast to the described expansion in the genetic repertoire in C. priscuii, here we suggest that the gene family encoding for photoreceptors is reduced when compared to related green algae. This alga also possesses a very small eyespot and exhibits an aberrant phototactic response, compared to the model Chlamydomonas reinhardtii. We also investigated the genome and behaviour of the closely related psychrophilic alga Chlamydomonas sp. ICE-MDV, that is found throughout the photic zone of Lake Bonney and is naturally exposed to higher light levels. Our analyses revealed a photoreceptor gene family and a robust phototactic response similar to those in the model Chlamydomonas reinhardtii. These results suggest that the aberrant phototactic response in C. priscuii is a result of life under extreme shading rather than a common feature of all psychrophilic algae. We discuss the implications of these results on the evolution and survival of shade adapted polar algae.

plant biology↗