Biology subjects

Tomcala, A.

Publications and source records attributed to Tomcala, A..

3 recordsLinked to original sources

bioRxiv2026

Transcriptomic and lipidomic profiles reveal higher thermal adaptability in a tropical versus a temperate isolate of Chromera velia

The apicomplexan alga Chromera velia is the closest known phototrophic relative of apicomplexan parasites (Sporozoa). Despite its scientific importance as a model for the evolution of parasitic Apicomplexa, only two strains are available in culture. The first isolate (SH), obtained from stony coral in the cold waters of Sydney Harbour, was used for the original species description. The second isolate (OTI) originates from tropical corals at One Tree Island in the Great Barrier Reef. In this study, we compare their growth, transcriptomic, and lipidomic profiles at 20{degrees}C and 26{degrees}C. Both strains grew faster at 26{degrees}C, yet they responded differently to higher temperature. In SH, warming downregulated nearly 85% of its thermally responsive genes, with motility-, cytoskeleton-, and lipid-associated genes most strongly affected, while at 26{degrees}C, SH retained higher expression of translation and nitrogen, amide, and peptide biosynthesis genes than OTI. OTI, by contrast, mounted a smaller, more balanced response and maintained stable expression of cilium, axoneme, and microtubule genes across both temperatures. The lipidomes of the two strains showed both shared and divergent responses. Both isolates sense and respond to increasing temperature in the same basic way, but OTI stabilizes its membranes, whereas SH redirects lipid synthesis from membrane lipids to storage lipids. OTI membranes were also constitutively less unsaturated than those of SH at both temperatures, consistent with a membrane already suited to warmer water that needs less remodeling. Our data show that two isolates of the same species, originating from different thermal environments, respond to elevated temperature through distinct transcriptomic and lipidomic programs. This suggests that the tropical OTI isolate is adapted to higher temperatures and demonstrates how reef-associated algae respond to rising ocean temperatures.

evolutionary biology↗

bioRxiv2026

Crystalline guanine packed within vacuoles serves as nitrogen store in Chromera velia

Nitrogen is an important element for all living organisms. Photoautotrophic organisms need to assimilate nitrogen from the environment, therefore changes in nitrogen availability have a strong influence on their growth and metabolism. Many microalgae have been known to contain crystalline inclusions, and recently, it has been shown that many of these consist of purines like guanine and thus must be linked to the cellular nitrogen metabolisms. The alveolate alga Chromera velia contains such guanine crystals, and during its lifecycle, the alga is thought to be subjected to strong changes in external nitrogen availability. Here, we investigated the formation or decline of crystalline guanine in dependence of the availability of inorganic nitrogen in the growth medium. Cells were examined using polarised light microscopy, Raman micro-spectroscopy, chromatography (HPLC), transmission and scanning electron microscopy. The cellular guanine crystal content decreased during nitrogen starvation and increased upon transfer of the cells back to standard growth medium containing nitrate. Raman micro-spectroscopy showed that the crystals were composed of anhydrous guanine in beta-polytype. They appear in unspecific positions throughout the cell, and staining with the green dye Lysotracker DND-26 suggests that they are within vacuoles. Stacks of crystals could be observed in cells via freeze fracture and freeze etching electron microscopy, which unambiguously showed a membrane around the crystal aggregates, in a similar arrangement as has been shown for guanine storage vacuoles (GSV) in Chlamydomonas reinhardtii. We developed a method to isolate the guanine crystals from whole cells, and were able to obtain crystals which retained their flat, plate-like structure, matching the electron microscopic observations from whole cells. The isolated crystals were shown to consist of nitrogen rich compounds via energy-dispersive X-ray (EDX) analysis, and Raman micro-spectroscopy confirmed that they consist of guanine.

cell biology↗

bioRxiv2019

An unprecedented combination of metabolic pathways in the cryptic plastid of a non-photosynthetic euglenophyte

Most secondarily non-photosynthetic eukaryotes have retained residual plastids whose physiological role is often still unknown. One such example is Euglena longa, a close non-photosynthetic relative of Euglena gracilis harbouring a plastid organelle of enigmatic function. By mining transcriptome data from E. longa we finally provide an overview of metabolic processes localized to its elusive plastid. The organelle plays no role in biosynthesis of isoprenoid precursors and fatty acids, and has a very limited repertoire of pathways concerning nitrogen-containing metabolites. In contrast, the synthesis of phospholipids and glycolipids has been preserved, curiously with the last step of sulfoquinovosyldiacylglycerol synthesis being catalysed by the SqdX form of the enzyme so far known only from bacteria. Notably, we show that the E. longa plastid synthesizes tocopherols and a phylloquinone derivative, the first such report for non-photosynthetic plastids studied so far. The most striking attribute of the organelle is the presence of a linearized Calvin-Benson (CB) pathway including RuBisCO yet lacking the gluconeogenetic part of the standard cycle, together with ferredoxin-NADP+ reductase (FNR) and the ferredoxin/thioredoxin systems. We hypothesize that FNR passes electrons to the ferredoxin/thioredoxin systems from NADPH to activate the linear CB pathway in response to the redox status of the E. longa cell. In effect, the pathway may function as a redox valve bypassing the glycolytic oxidation of glyceraldehyde-3-phosphate to 3-phosphoglycerate. Altogether, the E. longa plastid defines a new class of relic plastids that is drastically different from the best studied organelle of this category, the apicoplast. ImportanceColourless plastids incapable of photosynthesis evolved in many plant and algal groups, but what functions they perform is still unknown in many cases. Here we study the elusive plastid of Euglena longa, a non-photosynthetic cousin of the familiar green flagellate Euglena gracilis. We document an unprecedented combination of metabolic functions that the E. longa plastid exhibits in comparison with previously characterized non-photosynthetic plastids. For example, and truly surprisingly, it has retained the synthesis of tocopherols (vitamin E) and a phylloquinone (vitamin K) derivative. In addition, we offer a possible solution of the long-standing conundrum of the presence of the CO2-fixing enzyme RuBisCO in E. longa. Our work provides a detailed account on a unique variant of relic plastids, the first among non-photosynthetic plastids that evolved by secondary endosymbiosis from a green algal ancestor, and suggests that it has persisted for reasons not previously considered in relation to non-photosynthetic plastids.

evolutionary biology↗