Journal of Phycology最新文献

The brown macroalga Ascophyllum nodosum is a foundation species on intertidal rocky shores, where its perennial canopy and high productivity support key ecological functions. However, its population dynamics near the northern edge, where low temperatures and sea ice may challenge stability, are largely unknown. We followed the population structure, dynamics, and nutrient status of A. nodosum in the sheltered, subarctic Kobbefjord, Greenland from 2012 to 2019. Despite the northern location, population biomass (16–27 kg FW · m⁻²) was within the upper known range and was dominated by few large (max length: 109 cm), old individuals (observed age: up to 19 years; estimated mean lifespan: 37.5 years based on intrinsic mortality rate). Population density remained stable because of low mortality (0.019 · year⁻¹) and recruitment rates (0.010 · year⁻¹), sustained by an understory of small juveniles. Biomass increased 1.5-fold over the 8-year study, supported by high biomass productivity (3.3–8.1 kg FW · m⁻² · year⁻¹) that balanced branch loss and reflected a moderate biomass turnover time (2.6–6.3 years) of organic matter, underlying the apparent stability. Such overall population stability reflects a “biomass storer” strategy typical of environments with low disturbance and nutrient levels. The stability is remarkable given seasonal ice cover (2–7.5 months per year), large variation in average daily temperature (−3.9 to 15.4°C), and low nutrient supply. While ice breakup poses a risk of shoot abrasion, the ice cover likely provides protection against ice scouring. Enhanced growth during warmer summers and earlier ice break-up suggests faster turnover rates in the future to the extent nutrient availability can support it.

Non-heterocytous filamentous cyanobacteria are increasingly recognized as abundant and diverse microbial components of tropical and subtropical mangrove ecosystems. However, taxonomic studies of cyanobacteria in Thailand have largely focused on freshwater and artificial hypersaline environments, leaving mangrove-associated cyanobacterial communities understudied. In this polyphasic study, cyanobacterial mats were isolated and characterized from mangrove environments along the Andaman coastlines of Ranong and Phang-Nga provinces. Comparative analysis of morphology, salinity tolerance, habitat preference, 16S rRNA gene phylogeny and genetic similarity, 16S–23S ITS rRNA region phylogeny, secondary structure and percent dissimilarity supported the descriptions of Desertifilum andamanense sp. nov., Tigrinifilum phangngense sp. nov., Roseofilum epilithicum sp. nov., and Persinema corticola sp. nov., while justifying the continued recognition of D. fontinale and D. tharense. Two divergent ITS rRNA region operons in T. floridanum with different leader motifs, D1-D1', and D2 regions proved to be useful diagnostic markers of the ITS rRNA region for species and strain differentiation within Tigrinifilum. Our results underscore the importance of a polyphasic approach that also considers intragenomic ITS rRNA region variation to ensure robust and accurate taxonomic assessments of cyanobacteria. This study also provides records of the genera Desertifilum, Roseofilum, Tigrinifilum, and Persinema in Thailand, contributing to a more comprehensive understanding of the nation's diversity and biogeography of cyanobacteria.

Although the formation of “palmelloid-like” cells as a response to environmental stress has been sporadically reported in Chlorella sp., the association between morphological and molecular indices has been poorly understood. Hence, this study investigated the morphological and molecular effects of ethanol stress on C. sorokiniana by providing 0.0%, 0.025%, and 0.1% (v/v) ethanol. The results showed that cell growth, chlorophyll a, and photosynthetic efficiency were promoted under 0.025% ethanol. In contrast, the cells under 0.1% ethanol treatment were highly stressed; cell growth and physiological activities were inhibited, the content of cellular lipid, carbohydrate, reactive oxygen species, and the cell volume increased, and palmelloid-like structures with copious cell envelopes and higher cell wall carbohydrate contents were observed. The transcriptomic gene set enrichment analysis showed that chitin binding and organelle organization were upregulated while the developmental process was downregulated. Genes for actin-related-2, auxin-biding 1, phosphatidylinositol 4-kinase alpha1, phosphatidylinositol 4-phosphate 5-kinase 2 isoform A, and cytokinesis dedicator 4 were downregulated, whereas polysaccharide export, putative polygalacturonase, carbohydrate deacetylase, chitin, cellulose biosynthesis, and unsaturation of fatty acids were upregulated, implying polysaccharide was incorporated into the cell wall, and the rigidity of the cell membrane was promoted. These results suggest the suppression of the developmental process and cytokinesis and the overexpression of microtubules and cell-envelope genes could be the driving force for palmelloid-like structure formation, which could enhance the survival of cells under stress conditions by reducing cell surface area, promoting the production of protective cover and settleability, and adjusting cell rigidity.

Detailed molecular and cytomorphological characterization of two toxic Pseudanabaena strains (NMCCC 011 and NMCCC 012), isolated from highly polluted shallow areas of Monospitovo Marsh (North Macedonia), was performed using a “polyphasic” approach. This involved morphological and ultrastructural characterization, phylogenetic assessment of the 16S rRNA gene, analyses of the 16S–23S internal transcribed spacer (ITS) rRNA region, and investigations of the mcyB gene. The 16S rRNA gene phylogenetic analysis and the ITS rRNA region analyses confirmed that strain NMCCC 011 was a novel species for which we have proposed the name Pseudanabaena vesniana sp. nov., whereas NMCCC 012 represented a novel variety of Pseudanabaena suomiensis, here designated as P. suomiensis var. macedonica. The overall 16S rRNA gene phylogenetic analysis grouped Pseudanabaena into four large clades. Two of them comprised the primary lineages of diversification, hosting most Pseudanabaena sensu stricto infrageneric units. Most of these units formed distinctly recognizable subclades corresponding to different Pseudanabaena species (Cyanobacteriota); however, some strains were misidentified, leading to several scattered species through different subclades within the genus. Additionally, the genus Pseudanabaena was determined to be polyphyletic, with some strains clustering within the genera Tumidithrix and Thalassoporum (Cyanobacteriota). The 16S rRNA gene sequence identity within Pseudanabaena sensu stricto ranged from 95.7% to 99.9%, while the identity with Tumidithrix, Thalassoporum, and Thermostichus (Cyanobacteriota) ranged from 87.6% to 92.0%. Furthermore, both strains NMCCC 011 and NMCCC 012 produced microcystins and 2-methylisoborneol. The production of microcystins was confirmed by genetic and enzyme-linked immunosorbent assay (ELISA) analyses. Through this study, we report the presence of the mcyB gene in Pseudanabaena.

Diatoms are important primary producers in aquatic ecosystems. Most of them are photoautotrophs and have evolved to thrive under diverse environmental conditions from the poles to the tropics. However, some diatom species such as Nitzschia putrida have lost photosynthesis and have therefore become free-living secondary heterotrophs. Thus, these diatoms provide unique opportunities to study the evolutionary processes required to thrive without photosynthesis and independent of a resource-providing host. They may also provide a chassis for reverse engineering photosynthesis in eukaryotic organisms. Here, we have developed a genetic transformation system for N. putrida using a biolistic approach. By leveraging genome and transcriptome data, we identified the nicotinamide adenine dinucleotide hydride (NADH)-ubiquinone reductase complex 1 promoter as a robust candidate for driving transgene expression. Through Golden Gate Cloning, we engineered plasmids, including the selectable marker nourseothricin and the reporter eGFP. An evaluation of transformation efficiency confirmed the successful integration and expression of the transgenes. Fluorescence microscopy demonstrated the expression of eGFP in the transformed cell lines, which retained a growth phenotype similar to that of the wild type cells. Thus, our work in combination with the available genome and transcriptome of N. putrida enables reverse genetics with a free-living secondary heterotroph.

Phosphoenolpyruvate carboxykinase (PEPCK) is involved in the conversion of phosphoenolpyruvate (PEP) to oxaloacetate (OAA). In addition to playing a role in gluconeogenesis in various organisms, PEPCK also functions in the C₄ cycle to concentrate CO₂ for photosynthesis in some C₄ plants. Brown algae harbor genes related to the C₄ cycle, including the PEPCK gene, and are proposed to employ a C₄ cycle-like pathway. However, little is known about the CO₂-concentrating mechanisms and the properties of the enzymes involved in brown algae. Here, we obtained soluble recombinant PEPCKs of five brown algae and carried out biochemical analyses. The five PEPCKs were ATP-dependent and displayed similar or higher specific activities compared with their counterparts from other organisms. Phosphoenolpyruvate carboxykinase from Ishige okamurae (Io-PEPCK) exhibited the highest specific activity in both carboxylation and decarboxylation directions, with values of 48.4 and 63.3 μmol · min⁻¹ · mg⁻¹, respectively. Additionally, Io-PEPCK displayed a k_cat/K_mHCO3 value of 9.2 × 10³ · M⁻¹ · s⁻¹, much higher than those of previously characterized PEPCKs. The response of PEPCK activity to various metabolites showed that citrate and malate inhibited the carboxylation but promoted the decarboxylation activity of Io-PEPCK. Various ATP concentrations resulted in different degrees of inhibition on the carboxylation activity of PEPCK, suggesting that ATP concentration potentially regulates PEPCK activity in brown algae. The analysis of cell extracts from I. okamurae suggested that PEPCK rather than PEPC dominates the carboxylation in this brown alga. Based on previous knowledge and the results presented here, a model for a C₄ cycle-like pathway in brown algae has been proposed.

Rhodolith collections in British Columbia have historically been limited, and published regional species diversity data are poor. The acquisition of recent collections, notably from rhodolith beds in Haida Gwaii, provided an opportunity to assess diversity in these waters. The DNA barcode markers COI-5P, rbcL-3P, and psbA were used to identify unique genetic groups, which were then placed into a phylogenetic context with other coralline algae and subsequently observed anatomically. These analyses uncovered six rhodolith-forming species: two known, viz. Boreolithothamnion phymatodeum and Boreolithothamnion soriferum; a species provisionally called Boreolithothamnion sp. 1heterocladum; and three novel species described here, viz. Boreolithothamion astragaloi sp. nov., Boreolithothamnion tanuense sp. nov., and Rhodolithia gracilis gen. et. sp. nov., which comprises three varieties. Of particular interest, sequences of the ITS rDNA region showed the variety Rhodolithia gracilis var. gracilis × ramosa var. nov. to be a hybrid of the other two varieties: Rhodolithia gracilis var. gracilis var. nov. and Rhodolithia gracilis var. ramosa var. nov. Although understanding the full extent of BC rhodolith beds will require additional sampling, these findings indicate that rhodoliths are widespread and diverse in British Columbia.

Transcriptomic information is still scarce for seaweeds, especially for species from tropical regions. Laboratory-based physiological studies of some red algae have shown that they can tolerate temperatures that exceed those observed in their natural conditions. To understand the molecular mechanisms related to this tolerance, we chose as a model the agarophyte red alga Gracilariopsis tenuifrons and analyzed transcriptomic profiles at two different temperatures: 25°C (control temperature) and 33°C (stress temperature). Under the stress temperature conditions, only a relatively small percentage of genes were differentially expressed compared to the control temperature (5.75% were down-regulated and 5.25% were up-regulated at 33°C). Analysis of the predicted functions of the differentially regulated genes indicated enrichment in DNA-associated processes for the up-regulated genes and enrichment in gene ontogeny categories related to photosynthesis and membrane-associated processes for the down-regulated genes. The de novo transcriptome data provided in this study is a valuable scientific resource for future comparative research on red algae at stress conditions.