Journal of Phycology最新文献

A major challenge faced by kelp aquaculture operations is the control of contaminants, including by marine ciliates. Biokos® is a commercially available treatment for ciliate parasites in fish, in which the active ingredient is a viscosin-like lipopeptide surfactant. This study aimed to determine whether Biokos® is effective at controlling ciliate contamination in Saccharina latissima cultures without impacting gametophytes. Two experiments were conducted. Biokos® was first added to a live ciliate culture, and mortality was compared to a control. Subsequently, Biokos® was added to a culture of S. latissima gametophytes. The growth, density, and reproduction of gametophytes were compared to a control. Biokos® was highly effective at destroying ciliates within 24 h of treatment. We observed no impact on the vegetative growth of gametophytes. However, Biokos® did reduce gametophyte densities and may have had an impact on adherence. Biokos® also induced higher egg and sporophyte production in female gametophytes, potentially as a response to changes in pH associated with the treatment. There is potential for Biokos® to be effective at controlling ciliate contamination in gametophyte cultures, and at this stage, we would recommend treatment at manufacturer-recommended doses, along with appropriate buffering to maintain the pH of the culture. Further research is recommended on the identity of ciliate species contaminating gametophyte cultures and the response of different kelp species to Biokos®. Additionally, we would recommend that Biokos® now be tested in a commercial hatchery setting to identify impacts on S. latissima throughout the cultivation process and to determine optimal dosing procedures.

For the freshwater red algal order Batrachospermales, the number of plastid genomes available is relatively small compared to the number of genera. Fully assembled plastid genomes can provide insights into plastid evolution and crucial data for phylogenetic reconstruction. In the present study, 18 plastid genomes were generated for a total of 40 plastid genomes from 38 species representing 18 of the 23 genera. The greatly expanded dataset allowed for comparison of the plastid genome structural characteristics with the other orders in the Nemaliophycidae and inference of the phylogenetic relationships of the genera within the order. Results showed the plastid genomes had either one or two RNA operons, and this variation could be intrageneric. All plastid genomes had the chlB gene with an intron like all Nemaliophycidae but lacked the apcF gene present in all Nemaliophycidae. The loss of the pbsA gene was variable in the Batrachospermales and the Nemaliophycidae. Phylogenetic analysis using a 126-gene concatenated dataset produced a fully supported Batrachospermales. In addition, generally high support for the relationships among the genera resulted in the most robust phylogeny to date. Nevertheless, the phylogeny also highlighted that potentially more data will be needed to resolve the relationship among sections of Nothocladus and other related genera. Overall, the Batrachospermalean genera were split into two well-supported lineages, which had been noted in other studies using plastid and mitochondrial genomes. However, we lack a combination of characters to distinguish these two lineages, as the morphological characters to describe taxa are shared between them.

The green alga Pleodorina japonica is an interesting volvocine species that harbors abundant rickettsial endosymbionts ("MIDORIKO") within its cytoplasm. However, the diversity and transmission of these endosymbionts within the species remain unclear. In this study, we examined the presence or absence of "MIDORIKO" and the genetic diversity in 21 culture strains of the host P. japonica population from various localities in Japan. Genomic polymerase chain reactions using "MIDORIKO"-specific primers and 4',6-diamidino-2-phenylindole-staining demonstrated that only five of the 21 strains harbored "MIDORIKO." The 16S ribosomal DNA sequences of "MIDORIKO" from these five strains (1148 bp) were identical to each other and distinct from the sequences of the rickettsial endosymbionts harbored by other algal species and protists, suggesting that "MIDORIKO" from P. japonica is specific to P. japonica. The phylogenetic results for the 21 host strains, which were resolved based on three nuclear genes encoding oxygen-evolving enhancer protein 1, F1F0 ATP synthase subunit beta and actin disagreed significantly. None of the three gene phylogenies supported the close relationship of the five "MIDORIKO"-harboring strains. A recombination test using the three concatenated genes provided strong evidence of recombination. Therefore, gene flow by sexual reproduction has likely occurred in the natural habitats of P. japonica. The transmission of "MIDORIKO" among different P. japonica genotypes could also be considered to occur via sexual reproduction, although it is likely infrequent via that method given the sporadic nature of "MIDORIKO" within the P. japonica population. Although P. japonica exhibits homothallic sexual reproduction, the present genetic data demonstrate that it is undoubtedly a biological species.

The canopy-forming feather boa kelp Egregia menziesii exhibits remarkable morphological variability across its geographic range. Regional morphotypes of Egregia were once considered separate species, but they were not determined to be genetically distinct; instead, their morphology was thought to reflect local physical or environmental conditions. Although morphological variation in Egregia has long been observed and was previously characterized through field surveys in the early 2000s, we revisited this topic using digital morphometrics (i.e., image analysis) of 1624 macroalgal herbarium specimens from California dating back to the 19th century. We observed that the morphology of Egregia (rachis texture, lateral blade shape, and blade or pneumatocyst density) varied along a latitudinal gradient and could be predicted by seawater temperature and wave height. We also identified some region-specific morphological changes in recent decades. Further, the monthly presence or absence of sporophylls in southern-region specimens provided preliminary evidence into the reproductive phenology of Egregia. Herbarium collections are invaluable for studying patterns in morphology because they showcase inter- and intraspecific variability and establish a baseline for comparison through time. Integrating natural historical and contemporary data will be critical for understanding and predicting future trends in the context of ocean warming.

Despite recent efforts in taxonomic revision of phylogenetically basal photosynthetic cyanobacteria, cryptic diversity and recurrence of simple plesiomorphic morphotypes has continued to appear in phylogenies with poorly characterized "Synechococcus" and "Pseudanabaena" strains. Herein, one of the prominent undefined unicellular lineages was resolved as a monophyletic group of taxa that have lost multicellularity within the otherwise filamentous order Pseudanabaenales. Genome sequencing coupled with the classical polyphasic taxonomic analysis based on the 16S rRNA gene and the ITS rRNA region sequence comparisons, light and transmission electron microscopy, and source habitat record have congruently supported the description of two novel genera, Portococcus, with four new species, and Pseudanabaenococcus, with a single new species. The whole-genome phylogeny was essential for the accurate assessment of phylogenetic relationships between the genera and families and is hereby highly recommended as a new standard integrated in the polyphasic taxonomy of cyanobacteria. Records of the new taxa from a variety of freshwater habitats and one terrestrial cave habitat in geographically distant regions have indicated the need for further investigation to discover the full extent of cryptic diversity in these deep-branching clades. The loss of filamentous forms within the first group in cyanobacterial evolution that had invented it offers an excellent model for future study of the genetic and physiological mechanisms of early prokaryotic multicellularity.

Diatoms are known for their extraordinary species richness, cornerstone roles in aquatic ecosystems, and immense contributions to the global cycling of carbon, oxygen, and silica. For nearly 2 centuries, taxonomic classifications of diatoms have been based on interpretations of their feature-rich, silica cell walls. These classifications, in turn, have been used to make broad inferences about diatom ecology and evolution, but decades of molecular phylogenetic research have shown that historical and contemporary classification systems do not reflect evolutionary history, severely limiting their utility and insights. We took advantage of recent advances in our understanding of the diatom phylogeny to develop the first entirely natural classification of diatoms, in which only monophyletic groups have been recognized and named. The classification is comprehensive, dividing 431 genera among 68 families, 44 orders, and 10 classes. Among these, seven classes, 13 orders, three families, and one genus are proposed as new. Although the new classification includes many areas of overlap with previous systems, one principal departure is the increased number of classes, which reflects that "centric" and "araphid" diatoms are comprised of multiple lineages recognized here as distinct classes. By providing a more accurate representation of phylogenetic relationships, the proposed classification facilitates clearer communication about all aspects of diatom biology.

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.

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.

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.