Journal of Phycology最新文献

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.

We conducted a survey of Synurales diversity in Florida (United States), focusing on two established hotspots—Ocala National Forest and Myakka River State Park—and two previously unexplored sites—Manatee Lake and Lake Lee. Using transmission electron microscopy (TEM), we identified 69 species, increasing the total number recorded from Florida to 90. Among these, three species—Mallomonas cornea sp. nov., M. laureana sp. nov., and M. joergenii sp. nov.—have been newly described based on detailed morphological and molecular analyses. We have also proposed a new combination, M. poseidonii comb. et stat. nov., and established a new section, Corneae sect. nov., based on molecular phylogenetics. Our findings revealed an independent emergence of ribbed scale shield ornamentation in M. joergenii sp. nov. and suggested that internal scale reticulation in M. laureana sp. nov. may be an adaptation to high UV irradiance in tropical environments. This study underscores the value of DNA sequence data in resolving taxonomic ambiguities, elucidating evolutionary patterns, and enhancing species recovery from type localities.

The euendolithic genus Kyrtuthrix was originally described in 1929 by A. Ercegović from the Dalmatian coast. Due to its isopolar filaments, Kyrtuthrix was classified within the cyanobacterial system as part of the family Scytonemataceae, even though trichomes tapering toward their ends represent a feature typical of the family Rivulariaceae. In the last decade, four new species of Kyrtuthrix have been described. Their sequences helped to establish Kyrtuthrix as belonging to the family Rivulariaceae. However, the new species demonstrated that Kyrtuthrix was not always euendolithic, as the new discoveries occurred on igneous rocks that were not susceptible to penetration by cyanobacteria. We were able to obtain sequences of the 16S rRNA gene, the 16S-23S ITS rRNA region, the rpoC1 gene, and rbcLX gene for phylogenetic analyses of two classical species of Kyrtuthrix—the type species K. dalmatica collected from the Dalmatian coast and K. maculans collected from the Pacific coast of Peru. Our analyses revealed that both taxa were related to the newly described Kyrtuthrix species, although they were not clearly separated by molecular character sets from the more recently described Nunduva. A third Kyrtuthrix species from the coast of France was characterized by us during this study but was intermediate in morphological structure and phylogeny between K. dalmatica and K. maculans and not given a specific epithet. If we relied on the 16S rRNA gene sequence evidence, Nunduva would have been collapsed into the older genus Kyrtuthrix. However, using multiple gene evidence, they formed sister clades and, therefore, have been treated as distinct genera in this manuscript.

The seaweed Gracilariopsis lemaneiformis is used for agar and abalone feed, but high summer temperature in the southern oceans of China limits the cultivation industry. Therefore, enhancing the heat tolerance of G. lemaneiformis is crucial for prolonging its growth period along with increasing production and economic performance. Proline, a key osmotic regulator, plays an essential role in stress responses, including drought, heat, cold, and high salinity. Here, we investigated the dynamic changes in proline accumulation and its metabolic enzymes response to high-temperature stress in G. lemaneiformis. Results showed that elevated temperatures significantly increased proline accumulation, stimulated the activities of its synthetases pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), while concurrently suppressed the activity of its degrading enzyme proline dehydrogenase (ProDH). Pearson correlation analysis displayed a stronger positive association between proline level and OAT activity than with P5CS or pyrroline-5-carboxylate reductase (P5CR) activity, as well as a negative correlation with ProDH activity. Furthermore, exogenous 24-epibrassinolide, trehalose, and ornithine increased OAT activity or its gene transcription, while salicylic acid induced P5CS activity and P5CR2 transcriptional levels, which all resulted in the enhanced proline accumulation. Finally, bioinformatics analysis revealed that GlOAT contains a predicted PLP-binding domain, exhibits a high likelihood of mitochondrial localization, and shows a high degree of phylogenetic conservation. In summary, this study demonstrated that OAT is the critical enzyme involved in proline synthesis under high-temperature stress, which might provide a foundation for future transgenic breeding to improve high-temperature tolerance in G. lemaneiformis.

Coastal regions are complex habitats, where multiple natural and anthropogenic drivers can interact to affect the survival and growth of marine organisms. The giant kelp Macrocystis pyrifera is sensitive to increasing seawater temperatures and susceptible to marine heatwaves. Light availability and hydrodynamics can also affect the growth, morphology, and resilience of this species. In this experiment, juvenile sporophytes of M. pyrifera from Scorching Bay, Wellington, Aotearoa, New Zealand, a were exposed to a combination of simulated marine heatwaves at one of four different temperatures (20, 22, and 24°C compared to a 16°C control), one of two irradiance levels (shaded: 0.9 mol photons · m⁻² · d⁻¹ or ambient: 1.4 mol photons · m⁻² · d⁻¹), and one of two flow speeds (5.3 cm · s⁻¹ or 6.1 cm · s⁻¹) in a fully factorial design. Simulated heatwaves lasted for 21 days, with temperatures ramped by 2°C · d⁻¹, followed by a 21-day recovery phase. The heatwave treatments represented severe heatwaves in present day or hypothetical future conditions, whereas the control represented historical average summer sea temperatures in Wellington, and 21 days represented a realistic duration for heatwaves in this region. Temperature was the main driver of negative physiological impacts, with 100% of sporophytes dying within 42 days of exposure to a 24°C heatwave. Sporophytes experienced 44% mortality at 20°C and 81% mortality at 22°C, and growth rates declined significantly with increasing temperature. However, survival rates were modified by light and water velocity, with 56% of sporophytes surviving under a combination of ambient light and fast water velocity, compared with less than 50% under each of the other light-velocity combinations. Light limitation also reduced sporophyte survival, growth rates, and effective quantum yield. Water velocity alone did not significantly affect sporophytes, but flow speeds had interactive effects with temperature and light. The findings of this experiment suggest that M. pyrifera at sites with optimal environmental conditions, including low sediment loads and fast tidal flows, could be more resilient to marine heatwaves, as long as temperatures do not exceed critical thresholds for survival.

Numerous cyanobacterial strains previously identified as Scytonema hyalinum were determined to be phylogenetically distant from the type species of Scytonema, S. hofmannii. Morphological and molecular evidence suggests this distinct clade necessitates placement in a new genus, and we have described Kalymmatonema gen. nov. herein. Kalymmatonema has been demonstrated to exhibit five ribosomal operons, all of which differed in both sequence and secondary structure of conserved helical domains in the 16S–23S internal transcribed spacer rRNA region. Four of these operon copies were highly similar in 16S and 23S rRNA gene sequences, whereas the divergent fifth copy is thought to represent a whole-operon horizontal gene transfer event. Through in-depth analysis, we were able to recognize seven species new to science, the type species K. desertorum sp. nov., K. arcangelii comb. nov., K. chimaera sp. nov., K. ethiopiense sp. nov., K. gypsitolerans sp. nov., K. mateoae sp. nov., and K. oahuense sp. nov. We also created the new combination, K. hyalinum comb. nov., in order to include the original Scytonema hyalinum in this new genus based upon the common morphological feature of a mucilaginous apical cap on the trichomes. Kalymmatonema displays a complex evolution of its ribosomal operons, with evidence not only of horizontal gene transfer but also of internal rearrangements and mobile genetic elements that have transposed the tRNA-containing region of the ITS rRNA region among the four similar operons. Additional investigation of the evolutionary history of this interesting genus will likely lead to a better understanding of the processes shaping ribosomal evolution in cyanobacteria.