Journal of Phycology最新文献

The coccolithophore Helicosphaera carteri is an understudied, yet ecologically and biogeochemically important, marine calcifier. Hence, its response to ocean acidification has implications for ecosystem function and the marine carbon cycle. Here we employed dilute batch cultures featuring a coupled C-system manipulation (295, 444, and 600 μatm CO₂) to analyze the response of H. carteri in terms of growth rate and particulate carbon production, two key eco-physiological and biogeochemical parameters. We highlight that both growth rate and organic carbon production are CO₂ limited at 295 µatm but are not proton inhibited at 600 µatm of CO₂. This finding, combined with the maintenance of a stable inorganic production rate, places H. carteri among the coccolithophores less sensitive to seawater acidification. In addition, we tested a widely applied assumption underpinning the determination of carbon production, namely the constancy of particulate carbon quotas over the course of a dilute batch culture. We determined that the assumption holds true, an important validation of a method used in many publications.

Undaria pinnatifida is an economically important kelp that is extensively farmed in East Asia. Increasingly severe ocean warming makes it urgent to breed new cultivars that are resistant to higher temperatures. Breeding of triploid sporophytes is a potential way to achieve this purpose. Diploid gametophytes were previously produced via apospory from heterozygous sporophytes; however, their sex was not pure, making it difficult to conduct a precise cross. In the present study, we addressed this issue by means of obtaining aposporous diploid gametophytes from doubled haploid sporophytes that were produced by self-fertilization of a monoicous gametophyte. The sex of the aposporous diploid gametophytes was determined to be male. We crossed the male diploid gametophytes with three female haploid gametophyte clonal lines and obtained three hybrid sporophyte lines, which were identified to be triploid using flow cytometry analysis. We cultivated the three triploid lines in the open sea and evaluated their economic traits in April. Their total length and blade length were significantly higher than the control cultivar despite their cultivation period being ~2 months shorter than that of the control. Obvious decay was observed in the control, but not in the triploid sporophytes, suggesting that they sustained growth in higher temperatures. The triploid sporophytes formed sporophylls but were not able to release spores in the reproductive season, and thus, they were determined to be sterile. This study provides a novel and precise means for breeding triploid sporophytes in U. pinnatifida, which is expected to be useful for breeding triploid cultivars superior to the current diploid cultivars.

Asparagopsis taxiformis has high potential to mitigate enteric methane emissions from livestock due to its high bromoform content. However, the current supply of gametophytes is limited due to insufficient biomass. Year-round production of gametophyte can address insufficient biomass through a continuous supply of initial biomass from tetrasporophyte. In this study, we evaluated the effects of temperature (10, 20, and 30°C) and photoperiod (8:16, 12:12, and 16:8 h light:dark cycles), as well as irradiance (10, 20, 40, 80, 160 μmol photons · m⁻² · s⁻¹) and nutrient conditions (high nutrient: 500 μM nitrate and 30 μM phosphate; low nutrient: 50 μM nitrate and 3 μM phosphate) on the growth and reproduction of tetrasporophyte of A. taxiformis. Temperature was a key factor in both growth and reproduction, whereas photoperiod was a key factor in reproduction. Growth of tetrasporophyte was inhibited by 10°C regardless of photoperiod. The development of tetrasporangia was only observed at 20°C with an 8:16 h light:dark cycle. At 20°C with an 8:16 cycle, irradiance affected the development of tetrasporangia at high nutrient concentration. The development of tetrasporangia was observed at 20 and 40 μmol photons · m⁻² · s⁻¹, with the highest growth rate observed at 160 μmol photons · m⁻² · s⁻¹ without the development of tetrasporangia. These results suggest that controlling irradiance at 20°C on an 8:16 h light:dark cycle under high nutrient concentration can regulate the growth and reproduction of A. taxiformis tetrasporophyte during cultivation.

There has been an explosion of new Cyanobacterial taxa described within the last two decades. Cyanobacteria exhibit incredible ecological versatility and morphological variability, and thousands of species have already been described using “traditional” approaches (e.g., morphological features). However, DNA sequencing and other molecular tools have provided extensive evidence that the diversity of cyanobacteria is not necessarily congruent with morphology, as many morphological genera (e.g., Phormidium, Leptolyngbya, and Nostoc) are polyphyletic, and species within the genera are often morphologically indistinguishable, thus cryptic. Further confounding systematic assessments, newly erected taxa are often based on a single strain with one or two 16S rRNA gene sequences, may have incomplete formal descriptions, and lack indication of the employed species concepts. Here we have proposed a set of guidelines for cyanobacterial taxonomists. We have focused on the whole process of erecting new taxa: sampling, sequencing (including genomes), phylogenetic inference, phenotype characterization, species concepts, formal descriptions, and codes of nomenclature. Our hope is that these guidelines will help with the laborious but ever-rewarding task of identifying and describing the taxa within the world of cyanobacteria.

We sequenced the genome, transcriptome, and bacterial metagenome of Psammoneis japonica, a benthic, chain-forming, and araphid marine diatom. This combination of traits fills several gaps in genome sequencing coverage across diatoms. The nuclear genome (QPGO00000000) is an estimated 91.4 Mb in length, with 11,047 genes that comprise 18% of the total genome. Repetitive elements account for 33% of the genome, and other noncoding sequences comprise the remaining 49% of the genome. A global analysis of diatom genomes showed that repetitive elements are the principal driver of genome size variation in diatoms. Four complete genomes of Planctomycetota, ɑ-proteobacteria, and Bacteroidota were also recovered, and each had only moderate similarity to previously sequenced bacterial genomes. This finding supports the idea that bacterial species richness in the phycosphere is under-described and far exceeds the number of diatom host species, which themselves number in the tens to hundreds of thousands of species.

Dapis, along with other benthic cyanobacteria, forms large extensive proliferations (i.e., blooms, mats) that cover sand and seagrass beds across the coasts of Florida, United States. As these benthic cyanobacteria become more prevalent, especially in areas like the Indian River Lagoon (IRL), Sarasota Bay, Lemon Bay, Tampa Bay, and the Florida Keys, it is necessary to understand their diversity. To explore the diversity and identify the causative species of these nuisance marine benthic mats, growing and rafting mats were sampled. Three cyanobacterial isolates from marine mats across Florida were characterized and revealed to represent three novel species of Dapis, but with differing morphological features than those of previously described species. With the support of 16S rRNA gene sequence phylogeny, morphological evaluations, 16S–23S ITS rRNA region pairwise distances, and phylogenomic analyses, we have presented three novel species of Dapis. We have also provided taxonomically validated sets of Dapis genomes from several species.

The calcifying brown algal genus Newhousia (Dictyotales, Phaeophyceae) was previously reported from scattered Pacific localities, including Hawaii and Guam (Northern Hemisphere), French Polynesia, Papua New Guinea, and Vanuatu (Southern Hemisphere). We report here the occurrence of Newhousia from Southeast Asia, based on collections from Nha Trang Bay, Vietnam, representing a record from continental Asia and the westernmost occurrence of the genus. Multigene molecular analyses (psbA, rbcL, cox1, and cox3) identified the Vietnamese specimens as Newhousia imbricata. Morphological observations corroborated its diagnostic vegetative proliferation by eruption of new blade primordia. These findings extend the known distribution of Newhousia to Southeast Asia and highlight the ecological breadth of N. imbricata. They also emphasize the urgent need for expanded surveys across the Indo-Pacific to better resolve the genus's biogeography and diversity, which in turn will provide the foundation for deeper investigations into its dispersal mechanisms, evolutionary history, and reproductive biology.

We propose, based on a robust set of molecular and morpho-anatomical data of specimens from warm-temperate Japan, two new genera of non-geniculate coralline algae accommodating both attached and rhodolith-forming species: Magniporophytum gen. nov. containing M. variabile sp. nov. (the generitype) and M. epizoicum sp. nov. as well as Orientalilithon gen. nov. containing O. confluens sp. nov. (the generitype) and two undescribed Orientalilithon spp. Our multigene phylogenies inferred from psbA, rbcL, and SSU rDNA gene sequences demonstrated the distinct phylogenetic placements of Magniporophytum and Orientalilithon within the Hapalidiales; however, their generic positions have yet to be confirmed. In the psbA gene analyses, an undescribed Hapalidiales sp. 2 from Canada was separately grouped with the congeners of Magniporophytum from Japan, while an undescribed Lithothamnion sp. 5 from Taiwan was conspecific with Orientalilithon sp. 2 from Japan. Morpho-anatomically, the two new genera share some degrees of overlapping characters but can be distinguished by the shape of epithallial cells and the size of tetra/bisporangial pore openings compared to the surrounding rosette cells in surface view. The new genera differ from other phylogenetically related or morpho-anatomically similar genera by a suite of characters regarding epithallial cells, sub-epithallial initials, and tetra/bisporangial conceptacle characters. Within Magniporophytum, M. variabile and M. epizoicum are barely distinguishable, with a single difference in growth form. This study has highlighted a plausible generic character within the Hapalidiales along with the crypticity of coralline algae at both genus and species ranks and the extended distributions of Magniporophytum and Orientalilithon in the North Pacific Ocean.

The use of a combination of molecular and morphological data in biodiversity assessments is increasing the knowledge of turf-forming seaweeds, showing that cryptic diversity appears to be widespread. Polysiphonia sertularioides is a turf-forming filamentous alga with a presumed global distribution based on morphological identifications. Published molecular data, however, suggest that it represents a species complex with at least four lineages. To investigate the extent of the P. sertularioides complex and species distribution, we analyzed molecular and morphological data from 75 specimens from Australia, Brazil, Europe, and South Africa. The rbcL gene sequences were used for phylogenetic inference and species delimitation using Generalized Mixed Yule Coalescent, Poisson Tree Processes, and Assemble Species by Automatic Partitioning methods. Our analyses revealed that the P. sertularioides complex comprises 14–21 species, with 10 of the species recovered in all analyses. The species were recovered in two main, highly supported clades, one composed of European (Mediterranean and Macaronesian) species and the other composed of species from Australia, Brazil, Europe, Panama, and South Africa. Statistical analyses of a morphometric dataset of nine characters revealed that the species represents a morphological continuum, and although species from different regions were distinct, species from a region were morphologically indistinguishable. Most of the recovered species were restricted to a biogeographical region, rarely spanning different continents, with 10 endemic species. Our results revealed a case of true cryptic diversity in the P. sertularioides complex, highlighting the need for studies of small-sized algae (<5 cm).