ABSTRACT Rhynchomonads are ubiquitously distributed, small, colorless, heterotrophic flagellates with confirmed occurrences in diverse aquatic and soil habitats. To date, Rhynchomonas nasuta (Stokes 1888) Klebs 1892 is the commonly accepted species. However, phylogenetic studies revealed considerable genetic divergence, suggesting that isolates of this highly successful morphotype do not all belong to the same species. To resolve this discrepancy, we conducted an integrative taxonomic study combining morphological, autoecological, and molecular phylogenetic methods. While morphological characteristics proved insufficient for reliable species delineation, the integration of salinity tolerance experiments and phylogenetic analyses (18S and 28S rDNA sequences) revealed distinct and well‐supported clades. The obtained results support the description of nine new species ( Rhynchomonas minimamirounga n. sp., Rhynchomonas reesi n. sp., Rhynchomonas coloniensis n. sp., Rhynchomonas eder n. sp., Rhynchomonas mylnikovi n. sp., Rhynchomonas baltica n. sp., Rhynchomonas iris n. sp., Rhynchomonas pyschnyi n. sp., Rhynchomonas oltome n. sp.) within the genus Rhynchomonas . Additionally, we propose a neotype for Rhynchomonas nasuta and confirm Rhynchomonas metabolita Pshenin 1964 as valid species.
ABSTRACT Symbiosis is a fundamental biological strategy that enables metabolic complementation between distinct organisms. The amoeba Mayorella viridis establishes a photosymbiotic relationship with the green alga Chlorella , yet the physiological basis of this association remains poorly understood. Here, we compared symbiotic (green) and aposymbiotic (white) strains to quantify phenotypic effects of the symbiotic state. Cell size did not differ when the cells were fed but was significantly reduced in the white strain under starvation, indicating that Chlorella contributes to host stability under nutrient limitation. Motility was unaffected by symbiosis. In contrast, photoresponses, including positive phototaxis and photophobic responses, were completely abolished in the white strain, demonstrating that symbiotic Chlorella is essential for host photoresponse. Growth and survival were significantly reduced in the white strain under both constant light and constant dark conditions, indicating that the symbiont enhances both proliferation and starvation tolerance. Notably, under dark and nutrient‐limited conditions, intracellular Chlorella declined, suggesting digestion and utilization as an internal nutrient source. Photosymbiosis was re‐established by reintroducing isolated Chlorella into aposymbiotic cells, restoring green phenotype and photoresponse. These findings establish a reversible system and clarify the physiological roles of photosymbiosis in M. viridis .
ABSTRACT Monothalamous foraminifera are a highly diverse, paraphyletic assemblage of single‐chambered lineages characterized by an organic or agglutinated test or lacking any external covering. Traditional morphology‐based taxonomy divides them into the organic‐walled Allogromiida and agglutinated Astrorhizida. Molecular systematics showed that this division is not justified as different wall types occur within the same lineages. Twenty years ago, based on molecular phylogenetic data, the monothalamids were classified into 13 lineages, called clades. Since then, the diversity of monothalamids from different habitats and regions has been extensively studied both genetically and morphologically, and many new species and genera have been described. Here, we analyzed 70 sequences of the 18S rRNA gene, representing 66 described species. We also analyzed 23 sequences of the COI gene for selected taxa. Based on molecular phylogenetic analyses and available morphological data, we establish a new formal higher‐level taxonomy of monothalamous foraminifera. We introduce 5 new orders and distinguish 1 suborder and 34 families, of which 20 families are new. Our classification establishes a new taxonomic system that we hope will provide the foundation for organizing the vast diversity of monothalamous foraminifera revealed by recent studies.
ABSTRACT Under anaerobic conditions, Euglena gracilis degrades paramylon and synthesizes wax esters (WEs) while accumulating succinate in the culture supernatant. Succinate can either be converted to succinyl‐CoA by succinyl‐CoA synthetase (SCS) and enter the propionyl‐CoA biosynthetic pathway or accumulate extracellularly. Propionyl‐CoA serves as a primer for odd‐chain WE synthesis. Prior research revealed that knockout (KO) of the SCS α‐subunit (SCSα) nearly eliminated odd‐chain WE synthesis while preserving overall WE accumulation. In the present study, the effects of targeted modifications at anaerobic metabolic branch points on carbon allocation between WE synthesis and succinate accumulation were examined. SCSα KO increased succinate accumulation and markedly reduced odd‐chain WEs while largely maintaining total WE levels. Silencing mitochondrial NADP + ‐dependent malic enzyme (ME), which affects carbon allocation at the malate branch point between WE synthesis and the fumarate‐to‐succinate pathway, also increased succinate accumulation, although total WE accumulation decreased only slightly. Combining ME silencing with SCSα KO increased succinate accumulation to 8.9‐fold that of the wild type while retaining more than 75% of the WT total WE level. These findings demonstrate that targeted modification of anaerobic metabolic branch points can redirect carbon allocation toward succinate accumulation without abolishing WE biosynthesis in E. gracilis .
ABSTRACT Polar coastal waters are highly complex and productive ecosystems that experience increasingly higher average water temperatures, shallower and stronger stratification, and higher glacier‐melting rates. Yet, the environmental complexity and high microbial diversity within fjords pose challenges to understanding the impacts of these changes and the ecological processes driving them. Here, we studied protists and prokaryote communities, their distribution, and functional ecology along the northern Norwegian coast in summer 2019 using SSU rRNA gene metabarcoding. Physicochemical data provided insights into the main drivers for differences in plankton communities. We found significant differences in alpha and beta diversity among the different fjords and between the western (Vesterålen, Balsfjorden, and Lyngenfjord) and northern areas (Porsangerfjord, Laksefjord, and Tanafjord). Temperature, salinity, and phosphate are the main drivers for community composition differences, positively correlating with the western fjords and negatively with the northern ones. Metabarcoding analyses revealed dinoflagellates, cryptophytes, and ochrophytes as the most abundant groups on the north Norwegian coast and confirmed the bloom of the ichthyotoxic haptophyte Chrysochromulina leadbeateri in Balsfjorden. Our comprehensive spatial study of communities and key contributors across different fjords set a baseline for future environmental monitoring of these unique and productive ecosystems, which are subject to rapid environmental changes.
