Journal of Phycology最新文献

We have reported the first mitochondrial (GenBank accession PV035080) and chloroplast (GenBank accession PV035081) genomes for a representative of the gigartinalean family Dumontiaceae (Gibsmithia punonomaewa). High-throughput sequencing yielded both organellar genomes for the holotype specimen of Gibsmithia punonomaewa, a recently described species that is also a putative endemic to the mesophotic zone of the Hawaiian Islands. Gene content and order of the 26,428-bp mitochondrial genome are conserved relative to other available genomes of the Gigartinales. The genome contains 52 genes, including 25 protein-coding sequences (CDSs), 3 rRNAs, and 24 tRNAs, as well as one group II intron in a trnI-GAU tRNA. The chloroplast genome is 185,316 bp in length and contains 236 genes, including 203 CDSs, three rRNAs, and 30 tRNAs, and one group II intron in a trnM-CAU tRNA. Both organellar genomes displayed high synteny compared to close relatives in the order Gigartinales, with unique features restricted to several open reading frames. Phylogenomic analyses of the mitochondrial and chloroplast genomes with other gigartinalean representatives yielded well-resolved phylogenies that supported an early diverging position of the Dumontiaceae within the order Gigartinales.

Following the treatment of Saccharina diabolica, S. ochotensis, and S. religiosa as varieties of S. japonica, the same authors reported independent genetic groups corresponding to the original distributions of these species described in 1902. However, other population genetic studies have not supported these genetic groups corresponding to the varieties, and these varietal names have been applied predominantly to the Japanese population, despite S. japonica having a broader distribution in North Korea and the Russian Far East. This study reevaluated the taxonomic validity of these varieties by investigating the presence of corresponding genetic groups within Japan. We collected 475 individuals across its Japanese distribution, assigned them to five groups based on prior research, and genotyped them using 12 simple sequence repeat (SSR) markers. STRUCTURE analysis, discriminant analysis of principal components scatter plots, and isolation by distance analyses did not support the presence of distinct genetic clusters aligning with the described distributions of S. japonica and its varieties. Instead of confirming the previously demonstrated genetic groups, these analyses revealed either two or three large, geographically based genetic clusters or smaller genetic groups composed of neighboring localities. Consequently, this study has proposed the merger of the three varieties into a single species, S. japonica. Furthermore, we have proposed new combinations of several formae under S. japonica as they have retained their previous taxonomic status under Laminaria japonica or L. diabolica. Further research is required to assess the taxonomic validity of these formae.

Alkaline phosphatase (AP) plays an important role in phosphorus (P) cycling in aquatic ecosystems, particularly under nutrient limitation. In post-mining lakes of Czechia, periphyton forms extensive mats despite chronic P deficiency, suggesting dissolved organic P (DOP) may serve as a key P source. This study examines periphyton's ability to hydrolyze DOP via AP in three post-mining lakes in Czechia, assessing enzyme kinetic models, seasonal variation, and P-acquisition strategies. Seasonal shifts of apparent alkaline phosphatase catalytic efficiency (APCE) in periphyton, determined as the ratio of maximum hydrolysis velocity to Michaelis constant, have indicated that periphyton dynamically adjusts its enzyme activity. Periphyton exhibited rapid DOP turnover (tenths to tens of seconds) but had significantly lower APCE than phytoplankton. This suggests fundamental differences in P-acquisition strategies: Although phytoplankton relies on ambient DOP, periphyton retains and recycles P within its matrix. Retained P can be distributed throughout the periphyton taxa, supporting an idea of metabolic commensalism in periphyton assemblage. Our results underscored the adaptive role of periphyton community in buffering P availability through internal recycling, which, alongside P uptake from the lake water, supports persistence of periphyton in fluctuating P conditions. By sequestering and recycling P internally, periphyton alters lake-wide P dynamics, reduces P availability for phytoplankton, and potentially influences ecosystem productivity. Furthermore, this research has highlighted the limitations of applying simple Michaelis-Menten kinetics to describe complex enzymatic processes in natural ecosystems, emphasizing the need for models that better capture enzymatic heterogeneity and environmental interactions.

To chemically differentiate the three pelagic Sargassum morphotypes co-occurring in floating rafts and drifting across the Atlantic Ocean before stranding on West African, Caribbean, and Atlantic Mexican coastlines, we conducted an investigation of their metabolomic profiles. Hydroethanolic extracts from open-sea raft specimens were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS²), and the resulting spectra were processed through feature-based molecular networking with MetGem software. Several glycolipids were putatively identified through spectral matching and manual annotation, predominantly associated with S. natans var. wingei, S. natans var. natans, and S. fluitans var. fluitans. These findings were corroborated by statistical analyses of ¹H NMR spectral fingerprints. This study represents a chemotaxonomic assessment of pelagic Sargassum utilizing molecular networking, demonstrating its efficient utility for putative chemomarker identification. We further discuss the taxonomic status of the three varieties in light of our chemical data, along with observed physiological distinctions among the morphotypes.

Caves and hypogean environments provide stable microclimates characterized by uniform temperatures, constant humidity, and low light levels. In such sites, extremely low light irradiance can support the growth of subaerial biofilms (SABs) dominated by unique photosynthetic communities of cyanobacteria accompanied by chlorophytes, heterotrophic bacteria, and fungi. This study aimed to apply a culture-dependent approach to uncover the diversity of cyanobacteria, green algae, and fungi from SABs of a cave in Northern Spain. We isolated a total of 58 cyanobacteria grouped into 21 genera based on their 16S rRNA gene sequences; 24 green algae grouped into 10 genera based on their SSU rRNA gene sequences, and 41 fungi fell into 13 genera according to phylogenies based on the ITS rRNA region between the 16S and 23S rRNA genes (ITS rRNA region). The SABs were dominated by cyanobacteria, which also reflected by high diversity, including calcium-carbonate sheath-producing species such as Geitleria calcarea and Scytonema julianum. Typical cave-inhabiting species such as Chalicogloea cavernicola, Timaviella karstica or Oculatella subterranea were also isolated, alongside potentially new genera and species. Associated green algae were predominantly located closer to the cave entrance and included various lineages of the genera Jenufa and Chromochloris. The fungal community directly derived from the SABs was dominated by decomposers, saprophytes, and phytoparasitic representatives such as Sporobolomyces, Stereum, and Phlebia, with a corresponding set of enzymes that were evaluated for all fungal isolates. The results strongly support the hypothesis that specialized cyanobacterial communities are often located in caves as a result of niche specialization.

Development and growth of microalgae are mainly sustained by two essential nutrients: nitrogen (N) and phosphorus (P). Although single-nutrient limitation has been extensively studied, the balance between N and P availability remains less explored. Scrippsiella acuminata is one of the most abundant dinoflagellates in coastal ecosystems due to its physiological plasticity, making it a key species in the understanding of acclimation to unbalanced nutrient supply. To test the acclimation of S. acuminata, semicontinuous cultures were exposed to six N:P ratios (1.6, 8, 16, 32, 90, 180). Parameters such as photosynthetic response, biovolume, carbon excretion, lipids, reactive oxygen species production, cell cycle, and alkaline phosphatase activity were analyzed. Growth, regular cell cycle progression, balanced carbon allocation carbon resource, and high photosynthesis efficiency occurred at balanced N:P ratios (16, 32). At low ratios (1.6, 8), growth was reduced but cells maintained active photochemistry, whereas high ratios (90, 180) led to an extension of the G1 phase leading to biovolume increase and a limitation of the protective capacity of non-photochemical quenching leading to reactive oxygen species accumulation. Carbon allocation followed a stoichiometric gradient where more limiting N:P ratios favored soluble extracellular polymeric substances and a pool of cellular carbohydrates production as an overflow mechanism to protect cells, whereas moderate limitation led to lipid accumulation as a metabolic reserve. These results not only highlight the plasticity of S. acuminata to acclimate to nutrient stress but also suggest that this species may be more vulnerable in P-limited environments and has a competitive advantage where N is the primary limiting factor.

RNA interference (RNAi) is a powerful tool for protein knockdown and is widely used in model animals and plants. Here, we implemented RNAi in Bryopsis, a green feather alga that develops a coenocytic thallus >10 cm in length without cytokinesis. In vitro-transcribed double-stranded RNA (dsRNA) was either mixed with extruded cytoplasm in the presence of polyethylene glycol and then regenerated into thalli or directly introduced into the cytoplasm by perfusion. Within several days, target-gene transcript levels decreased, and the expected phenotypes emerged, indicating effective RNAi. We designed dsRNAs for all 34 kinesin superfamily genes of a model Bryopsis strain, delivered them by both methods, and monitored chloroplast distribution and motility by microscopy. Knockdown of KCBP-type kinesin-14VI (Kin14VIa and Kin14VIb), which drive retrograde chloroplast transport in the moss Physcomitrium patens, and of the apparently Bryopsis-specific kinesin-14II (Kin14IIb) suppressed retrograde motility, resulting in apical chloroplast accumulation. In addition, RNAi of the Bryopsidales-specific kinesin-14VI (Kin14VIc) reduced both retrograde and anterograde movements, implying that multiple Kin14 motors contribute to chloroplast transport in Bryopsis. In contrast, knockdown of Kin12c, a member of the kinesin-12 family that is known to be essential for cytokinesis in land plants, caused basal chloroplast enrichment, indicating divergent evolution of this motor family in the green lineage. Together, these results establish RNAi as a robust loss-of-function approach in a coenocytic alga and reveal lineage-specific kinesins as key drivers of chloroplast motility within its giant cytoplasm.

Ceratocorys armata, C. gourretii, and C. horrida have historically been treated as distinct species based on morphology. Both field samples and cultured strains, however, exhibit continuous morphological variation and intergradations between these taxa. Here, strains from Viet Nam, Japan (Pacific Ocean), and France (Mediterranean Sea, Atlantic Ocean) were analyzed using integrated morphomolecular approaches. Cultured strains revealed morphological intergradations from C. horrida to C. armata and from C. armata to C. gourretii. Phylogenetic analysis based on the ITS1-5.8S-ITS2 rDNA region sequences and the SSU (18S) and LSU (28S) nuclear rDNA gene sequences confirmed the genetic identity of these three taxa for these markers. The ITS2 secondary structure comparisons—including C. malayensis from Viet Nam and Malaysia—further supported their conspecificity, while validating C. malayensis as a distinct species. Based on these data, we have proposed to treat them as formae: C. horrida f. horrida, C. horrida f. armata, and C. horrida f. gourretii. Furthermore, our results indicated that C. malayensis strains from Viet Nam are non-toxic. We have also provided morphological descriptions and illustrations of C. bipes and C. magna, two species rarely reported in the Asia-Pacific region, enhancing the taxonomic clarity of the genus.