Biology subjects

Malkovskiy, A.

Publications and source records attributed to Malkovskiy, A..

5 recordsLinked to original sources

bioRxiv2026

Dual-targeted NADK2 Links Mitochondrial Redox Homeostasis to Carbon Partitioning and Heterotrophic Growth in Chlamydomonas reinhardtii

NAD kinases (NADKs) can modulate NADP(H) levels across shifting environmental conditions. In Chlamydomonas reinhardtii, we localized CreNADK1 to the chloroplast, CreNADK3 to the cytoplasm, and CreNADK2 to both the chloroplast and mitochondria. Importantly, during mixotrophic (light + acetate) and photoautotrophic (light) growth, most CreNADK2 is chloroplast localized whereas an increased proportion resides in mitochondria when the cells are grown heterotrophically (dark + acetate). In Crenadk2 mutants, a diminished ability to synthesize mitochondrial NADP(H) inhibits the TCA cycle and markedly retards heterotrophic growth. In the light, photosynthesis becomes the primary energy source, and the presence of chloroplastic CreNADK1 enables near-normal growth in mutant cells, with inhibition of TCA cycle activity partially ameliorated via rerouting of acetate metabolism through the glyoxylate shunt, bypassing the TCA cycle and diminishing mitochondrial ROS production. These findings demonstrate spatial plasticity of NAD(H)Ks and the implementation of bypass metabolism to enable growth of Crenadk2 mutants.

cell biology↗

bioRxiv2024

Illuminating microbial mat assembly: Cyanobacteria and Chloroflexota cooperate to structure light-responsive biofilms

Microbial mats are stratified communities often dominated by unicellular and filamentous phototrophs within an exopolymer matrix. It is challenging to quantify the dynamic responses of community members in situ as they experience steep gradients and rapid fluctuations of light. To address this, we developed a binary consortium using two representative isolates from hot spring mats: the unicellular oxygenic phototrophic cyanobacterium Synechococcus OS-B (Syn OS-B) and the filamentous anoxygenic phototroph Chloroflexus MS-CIW-1 (Chfl MS-1). We quantified the motility of individual cells and entire colonies and demonstrated that Chfl MS-1 formed bundles of filaments that moved in all directions with no directional bias to light. Syn OS- B was slightly less motile but exhibited positive phototaxis. This binary consortium displayed cooperative behavior by moving further than either species alone and formed ordered arrays where both species aligned with the light source. No cooperative motility was observed when a non-motile pilB mutant of Syn OS-B was used instead of Syn OS-B. The binary consortium also produced more adherent biofilm than individual species, consistent with the close interspecies association revealed by electron microscopy. We propose that cyanobacteria and Chloroflexota cooperate in forming natural microbial mats, by colonizing new niches and building robust biofilms. SignificanceMicrobial mats are dense, layered communities with ancient origins and widespread occurrence, but how they assemble is not well understood. To investigate how microbial motility, physical interactions, and responses to light affect mat assembly, we developed a binary consortium from representative hot spring mat isolates. Individually, the Cyanobacteria and Chloroflexota isolates displayed significant differences in motility and biofilm formation. When combined, the consortium exhibited enhanced motility towards light and formed more robust biofilms. This model consortium approach complements in situ studies by directly testing the role of motility and physical cooperation in shaping microbial mats, and could inform biofilm applications in industrial settings.

microbiology↗

bioRxiv2024

Dramatic Changes in Mitochondrial Subcellular Location and Morphology Accompany Activation of the CO2 Concentrating Mechanism

Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for [~]50% of global photosynthesis, compartmentalize their Rubisco into a specialized structure known as the pyrenoid when the cells experience limiting CO2 conditions; this compartmentalization appears to be a component of the CO2 Concentrating Mechanism (CCM), which facilitates photosynthetic CO2 fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO2 limiting conditions, although a role for this reorganization in CCM function remains unclear. We used the green microalgae Chlamydomonas reinhardtii to monitor changes in the position and ultrastructure of mitochondrial membranes as cells transition between high CO2 (HC) and Low/Very Low CO2 (LC/VLC). Upon transferring cells to VLC, the mitochondria move from a central to a peripheral location, become wedged between the plasma membrane and chloroplast envelope, and mitochondrial membranes orient in parallel tubular arrays that extend from the cells apex to its base. We show that these ultrastructural changes require protein and RNA synthesis, occur within 90 min of shifting cells to VLC conditions, correlate with CCM induction and are regulated by the CCM master regulator CIA5. The apico-basal orientation of the mitochondrial membrane, but not the movement of the mitochondrion to the cell periphery, is dependent on microtubules and the MIRO1 protein, which is involved in membrane-microtubule interactions. Furthermore, blocking mitochondrial electron transport in VLC acclimated cells reduces the cells affinity for inorganic carbon. Overall, our results suggest that CIA5-dependent mitochondrial repositioning/reorientation functions in integrating cellular architecture and energetics with CCM activities and invite further exploration of how intracellular architecture can impact fitness under dynamic environmental conditions.

plant biology↗

bioRxiv2023

Thermo-sensitive condensation of SUF4 tunes flowering time in Arabidopsis thaliana

Intrinsically disordered proteins (IDP) lack stable tertiary structures, which allows them to change conformation and function under different physicochemical conditions. This may be highly advantageous for plants, which often use changes in their environment to elicit a variety of responses, including developmental events. For instance, some plants delay flowering in the fall and require exposure to winter temperatures as a cue to initiate flowering the following spring. Many of the genes involved in temperature-dependent flowering have been extensively studied in Arabidopsis, yet how plants coordinate their molecular states with seasonal temperature change is poorly understood. Here, we explore the role of temperature-sensitive phase separation of the IDP and flowering-time regulator, SUPPRESSOR OF FRIGIDA 4 (SUF4), in modulating flowering time. SUF4 has a well-defined role in regulating temperature-dependent flowering time by activating the master floral suppressor FLOWERING LOCUS C (FLC). We show that in plant nuclei, SUF4 is a temperature-sensitive protein that assembles into biomolecular condensates in warm temperatures (20{degrees}C). When temperatures cool (4{degrees}C), SUF4 nuclear condensates disassemble, causing SUF4 to disperse within the nucleoplasm. Additionally, we demonstrate that the number of SUF4 condensates quantitatively correlates with flowering time. Progressive alterations to the amino acid composition of SUF4s disordered region cause likewise progressive changes in temperature-dependent condensation both in vitro and in vivo, FLC transcription, and the onset of flowering. Lastly, we observe that SUF4 condensates coincide with the accumulation of other key flowering-time proteins (FRIGIDA and ELF7). These findings indicate that condensation of SUF4 likely plays a pivotal role in promoting flowering, possibly by concentrating and stabilizing regulatory factors needed for the transcriptional activation of FLC through temperature-dependent phase separation. This research suggests that in plants, IDPs can sense environmental cues and regulate critical developmental processes. One-Sentence SummaryEvidence suggest that Arabidopsis uses temperature-sensitive condensation to regulate FLC transcription and flowering time.

plant biology↗

bioRxiv2020

Hyaluronan Synthesis Inhibition Impairs Antigen Presentation and Delays Transplantation Rejection

A coat of pericellular hyaluronan surrounds mature dendritic cells (DC) and contributes to cell-cell interactions. We asked whether 4-methylumbelliferone (4MU), an oral inhibitor of HA synthesis, could inhibit antigen presentation. We find that 4MU treatment reduces pericellular hyaluronan, destabilizes interactions between DC and T-cells, and prevents T-cell proliferation in vitro and in vivo. These effects were observed only when 4MU was added prior to initial antigen presentation but not later, consistent with 4MU-mediated inhibition of de novo antigenic responses. Building on these findings, we find that 4MU delays rejection of allogeneic pancreatic islet transplant and allogeneic cardiac transplants in mice and suppresses allogeneic T-cell activation in human mixed lymphocyte reactions. We conclude that 4MU, an approved drug, may have benefit as an adjunctive agent to delay transplantation rejection.

immunology↗