Biology subjects

Grujcic, V.

Publications and source records attributed to Grujcic, V..

4 recordsLinked to original sources

bioRxiv2025

The path to dependence: stepwise genome evolution from a facultative symbiont to an endosymbiont in the N2-fixing diatom-Richelia symbioses

A few genera of diatoms are widespread in the oceans and form stable partnerships with N2-fixing filamentous cyanobacteria Richelia spp. A unique feature of the diatom-Richelia symbioses is the symbiont cellular location spans a continuum of integration (epibiont, periplasmic, endobiont) that is reflected in the symbiont genome size and content. In this study we analyzed genomes derived from cultures and environmental metagenome-assembled genomes focusing on characters indicative of genome evolution. Our results show an enrichment of short length transposable elements (TEs) and pseudogenes in the periplasmic endosymbiont genomes, suggesting an active and transitionary period in genome evolution. In contrast, genomes of endobionts exhibited fewer TEs and pseudogenes, reflecting advanced stages of genome reduction and increased host dependency in the endobionts. Pangenome analyses identified that endobionts streamline their genomes and conserve a majority of their genes in the core, whereas periplasmic endobionts and epibionts maintain larger flexible genomes, suggesting increased genomic plasticity. Functional gene comparisons with other N2-fixing cyanobacteria revealed that Richelia endobionts have similar patterns of metabolic loss but are distinguished by absence of specific pathways (e.g. cytochrome bd ubiquinol oxidase, lipid-A) that increase dependency and direct interaction with their respective hosts. In conclusion, our findings underscore the dynamic nature of genome reduction in N2-fixing cyanobacterial symbionts and demonstrate the diatom-Richelia symbioses as a valuable and rare model to study genome evolution in the transitional stages from a free-living facultative symbiont to a host-dependent endobiont.

microbiology↗

bioRxiv2024

Depth-dependent dynamics of protist communities as an integral part of spring succession in a freshwater reservoir

BackgroundProtists are essential contributors to eukaryotic diversity and exert profound influence on carbon fluxes and energy transfer in freshwaters. Despite their significance, there is a notable gap in research on protistan dynamics, particularly in the deeper strata of temperate lakes. This study aimed to address this gap by integrating protists into the well-described spring dynamics of [R]imov reservoir, Czech Republic. Over a two-month period covering transition from mixing to established stratification, we collected water samples from three reservoir depths (0.5, 10 and 30 m) with a frequency of up to three times per week. Microbial eukaryotic and prokaryotic communities were analysed using SSU rRNA gene amplicon sequencing and dominant protistan groups were enumerated by Catalysed Reporter Deposition-Fluorescence in situ Hybridization (CARD-FISH). Additionally, we collected samples for water chemistry, phyto- and zooplankton composition analyses. ResultsFollowing the rapid changes in environmental and biotic parameters during spring, protistan and bacterial communities displayed swift transition from a homogeneous community to distinct strata-specific communities. Epilimnion exhibited the prevalence of auto-, mixotrophic protists dominated by cryptophytes and associated with spring algal bloom-specialized bacteria. In contrast, meta- and hypolimnion showcased the development of protist community dominated by putative parasitic Perkinsozoa, detritus or particle-associated ciliates, cercozoans and excavate protists co-occurring with bacteria associated with lake snow. ConclusionsOur high-resolution sampling matching the typical dividing time of microbes along with the combined microscopic and molecular approach and inclusion of all the components of microbial food web allowed us to follow depth-specific populations successions and interactions in a deep lentic ecosystem.

ecology↗

bioRxiv2023

Towards high-throughput parallel imaging and single-cell transcriptomics of microbial eukaryotic plankton

Single-cell transcriptomics has the potential to provide novel insights into poorly studied microbial eukaryotes. Although several such technologies are available and benchmarked on mammalian cells, few have been tested on protists. Here, we optimized a microarray single-cell sequencing (MASC-seq) technology that generates microscope images of cells in parallel with capturing their transcriptomes. We tested the method on three species representing important plankton groups with different cell structures, the ciliate Tetrahymena thermophila, the diatom Phaeodactylum tricornutum and the dinoflagellate Heterocapsa sp.. Both the cell fixation and permeabilization steps were adjusted. For the ciliate and dinoflagellate, the number of transcripts of microarray spots with single cells were significantly higher than for background spots, and the overall expression patterns were correlated with that of bulk RNA, while for the much smaller diatom cells, it was not possible to separate single-cell transcripts from background. The MASC-seq method holds promise for investigating "microbial dark matter", although further optimizations are necessary to increase the signal-to-noise ratio.

genomics↗

bioRxiv2020

A freshwater radiation of diplonemids

Diplonemids are considered marine protists and have been reported among the most abundant and diverse eukaryotes in the world oceans. Recently we detected the presence of freshwater diplonemids in Lake Biwa, Japan. However, their distribution and abundances in freshwater ecosystems remain unknown. We assessed abundance and diversity of diplonemids from several geographically distant deep freshwater lakes of the world by amplicon-sequencing, shotgun metagenomics and CARD-FISH. We found diplonemids in all the studied lakes, albeit with low abundances and diversity. We assembled long 18S rRNA sequences from freshwater diplonemids and showed that they form a new lineage distinct from the diverse marine clades. Freshwater diplonemids are a sister-group to marine isolates from coastal and bay areas, suggesting a recent habitat transition from marine to freshwater habitats. Images of CARD-FISH targeted freshwater diplonemids suggest they feed on bacteria. Our analyses of 18S rRNA sequences retrieved from single cell genomes of marine diplonemids shows they encode multiple rRNA copies that may be very divergent from each other, suggesting that marine diplonemid abundance and diversity both have been overestimated. These results have wider implications on assessing eukaryotic abundances in natural habitats by using amplicon-sequencing alone.

microbiology↗