Journal of Phycology最新文献

Recent phylogenetic analyses of members of the Tolypothrichaceae (Nostocales, Cyanobacteria) based on 16S rRNA gene sequence data have demonstrated that the soil-inhabiting members of the family belong to a clade separate from the aquatic and subaerial members of the family. The soil-inhabiting species clade includes Spirirestis, a monophyletic taxon originally defined by its tight spiral coiling. Most of the soil-inhabiting species have been identified in the past as belonging either to Hassallia or Tolypothrix, which are subaerial and aquatic taxa, respectively. A comprehensive study of the terrestrial Tolypothrichaceae led us to conclude that all terrestrial Tolypothrichaceae should be included in the genus Spirirestis, even though most of those isolates lack the spiral coiling diagnostic of the genus. Using a polyphasic approach, we recognize seven distinct clades in Spirirestis, which we split into seven species: S. rafaelensis (the generitype), S. californica comb. nov., S. pseudoramosissima comb. nov., S. lignicolor sp. nov., S. williamsae sp. nov., S. hydroterrestris sp. nov., and S. atacamensis sp. nov. Spirirestis rafaelensis and S. californica are represented by multiple isolates, and we postulate that with time and further taxon sampling, some of the strains we included in these two species may be recognized as additional species. As the study of soil cyanobacteria continues, additional species of Spirirestis will likely be discovered and described.

The identity of a marine planktonic species that forms palmelloid colonies has remained enigmatic since the first observations during the Plankton Expedition in 1889. Initially identified as spores or chlorophyte cells, Gloeodinium marinum was described as an immotile coccoid dinoflagellate with Gymnodinium-like swarmers. In this study, we have reported observations of G. marinum from the Mediterranean Sea, including the type locality, the Southwest Indian Ocean, and the tropical Atlantic Ocean. The sequences of the SSU and LSU rRNA genes and the ITS rRNA region (ITS1-5.8S gene-ITS2) revealed that G. marinum is distantly related to congeneric species, the type species G. montanum, and G. viscum, while it is closely related to Prorocentrum canariense and P. compressum auct. mult., two planktonic species known to produce mucilage envelopes. These phylogenetic and morphological characteristics positioned Gloeodinium marinum as a member of Prorocentrum sensu stricto, and we have proposed to reclassify it with the new name Prorocentrum palmelloides nom. nov. This species differs from its closest relatives in its smaller size (~25 μm), roundly oval shape, and multiple mucilage envelopes. The recently divided cells showed hemispherical shape, and the flagella only appeared in naked swarmers after theca ecdysis. The morphological adaptation to a life within mucilage envelopes has contributed to its cryptic identity for more than 130 years.

Pennate diatoms are an ecologically and evolutionarily successful group of algae, dominating in sedimentary habitats where they form biofilms with high productivity and diversity. Their success has been attributed to directed motility, which is used to explore the microscale environmental gradients present in sediments, particularly regarding light, optimizing photosynthesis while avoiding photodamage. Some pennate diatoms can exhibit a process termed karyostrophy, the contraction of the chloroplasts toward the cell center when exposed to high light. Karyostrophy has long been hypothesized to play a photoprotective role; however, its light dependency and physiological effects remain poorly characterized. This study investigated the light-dependent kinetics and photophysiological effects of karyostrophy in the diatom Pleurosigma strigosum. Chloroplast contraction was found to be light-dependent, being induced under irradiances above 60 μmol photons · m⁻² · s⁻¹, with the rate and extent of contraction increasing with light intensity. The process was reversible, with chloroplasts returning to their original conformation under low light, although at a slower rate. Cell-level photophysiological measurements indicated that karyostrophy enhanced self-shading in proximal cell regions, improving the capacity of the cells to recover from light stress. Non-photochemical quenching (NPQ) was also affected by chloroplast contraction, with distal regions of the cell exhibiting significantly higher NPQ activation. These findings suggest that karyostrophy might serve as a complementary photoprotective mechanism, acting alongside whole-cell motility and NPQ. This study provides the first quantitative characterization of the light response of karyostrophy, highlighting its possible role in optimizing light utilization and protecting against photodamage.

The correct development of an organism is critical for its survival and reproduction, especially the early stages of establishment. Early developmental stages require close control and careful signaling between cells and genetic networks. Red algae also undergo critical developmental stages, but very little is known about these processes or their control. An important developmental signal is the redox state of a cell. The complex life cycle of red algae also involves the intricate development of the fertilized egg to produce diploid spores (carpospores). We examined the effect of redox perturbation on the life cycle of Bostrychia moritziana, focusing on critical stages of spore development, the formation of meiospores (tetraspores), and the development of the diploid carposporophytes. Our results showed that spore development follows a distinct pattern of asymmetrical division and differentiation, regulated by reactive oxygen species (ROS) signaling. Reactive oxygen species were observed to accumulate specifically at the dividing plane of the central cell, suggesting their importance in cell division. Treatments with various redox-altering compounds, including hydrogen peroxide, antioxidants, and inhibitors of NADPH oxidase and calcium signaling, significantly impacted spore development, carposporophyte formation, and the development of tetrasporangial branches. Our results demonstrated that short-term redox perturbations during critical developmental stages can have far-reaching consequences on the morphogenesis of B. moritziana, affecting both immediate growth patterns and long-term developmental trajectories.

Interactions between phytoplankton and bacteria play critical roles in shaping marine ecosystems. However, the intricate relationships within these communities—particularly in rapidly changing polar environments—remain poorly understood. We use targeted methods to directly characterize the microbiomes of individual colonies of Phaeocystis antarctica, a keystone phytoplankton species in the Southern Ocean, and showed that colony microbiomes were consistent across individual colonies collected 108 nautical miles apart. These results suggest that hosting specific colony microbiomes is a shared trait across colony-forming Phaeocystis species, with different species hosting colony microbiomes suited to their respective environments. The bacterial orders Alteromonadales, Oceanospirillales, and Sphingomonadales dominated the microbiomes of all field-collected P. antarctica colonies. The relative abundances of bacterial taxa comprising the majority of field-collected colony microbiomes—for example, Paraglaciecola sp. (Alteromonadales) and Nitrincolaceae (Oceanospirillales)—correlated with Phaeocystis abundance in surface waters, highlighting their potential roles in bloom dynamics and carbon cycling. After a year of laboratory culture, we observed a reduction in colony microbiome diversity, and Caulobacterales, Cellvibrionales, and Rhodobacterales dominated the cultured colony microbiomes. Notably, abundant genera in field-collected colony microbiomes that were lost in culture were psychrophiles. The shift in microbiome structure emphasizes the importance of field-based studies to capture the complexity of microbial interactions, especially for species from polar environments that are difficult to replicate in laboratory conditions. This research provides valuable insights into the ecological significance of prokaryotic interactions with a key phytoplankton species and underscores the necessity of considering these dynamics in the context of climate-driven shifts in marine ecosystems.

Symbiodiniaceae are crucial dinoflagellate symbionts for corals. They are affected by climate change-induced temperature rises that lead to coral bleaching, impacting coral reefs' health. Cryopreservation offers a solution to ensuring long-term storage of this species, preserving genetic diversity and viability. However, cryoinjury's impacts on glycan, a class of biomolecules with diverse biological roles including the initiation of coral–Symbiodiniaceae symbiosis, remain unknown. Thus, we examined the glycan profile of Breviolum psygmophilum cells cultured for varied periods post-thaw. The cells were subjected to two-step freezing with 2 M methanol as the cryoprotectant, and were cryopreserved for 2 h, then thawed and cultured. Lectin Array 70 was used to analyze glycan profiles of B. psygmophilum before and after cryopreservation. The results indicated that fucose and mannose differed significantly from N-acetyllactosamine, indicating its low presence in non-cryopreserved cells. Cryopreserved B. psygmophilum showed significant changes in fucose and mannose content, and several lectins contributed to the abundance of their respective carbohydrate moieties. These carbohydrates may affect cell division, repair, and energy. Lectins Gal1, CNL, DSA, BC2LCN, GRFT, HHA, NPA, Orysata, ConA, Gal3, and ACG changed in content post-cryopreservation, which may have been to mitigate the cryopreservation-induced stress, similar to their response to other stresses, while vital biological processes were maintained. This study sheds light on Symbiodiniaceae glycan profile alterations post-cryopreservation, which could influence Symbiodiniaceae's ability to establish symbiosis with corals thus highlighting the need to optimize cryopreservation protocols to minimize glycan alterations and enhance Symbiodiniaceae preservation, ultimately supporting coral reef conservation efforts.

Sulfur (S) is a key element in multiple metabolic pathways of phytoplankton cells. The effect of S availability on phytoplankton elemental quotas and stoichiometry has been addressed in few studies, using a limited number of species and with contradictory results. Using high-temperature combustion oxidation and X-ray fluorescence methods, we measured the concentrations of micro- and trace elements in monocultures of 20 marine phytoplankton species, grown with different sulfate concentrations representing those of early and modern oceans. We found that, independently from the sulfate concentration in the media, the red lineage species had higher S quotas than those of the green lineage, resulting in lower C:S (93) and higher S:P (1.06) than the green lineage species (226 and 0.76, respectively). This suggests a genetic constraint in the S quota and aligns with the sulfate facilitation hypothesis, shedding light on a metabolic basis for the expansion of the red lineage algae and their current dominance in ocean waters. We also have shown a physiological response of phytoplankton cells to different sulfate availability, by either decreasing phosphorus or increasing zinc quotas. The P response was more characteristic in the red lineage, with higher S requirements and metabolic S fluxes, while the Zn response was independent of genotypic constraints or plastid type.

Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide CO₂ removal approach for climate change mitigation and can be implemented with various alkaline materials that convert dissolved CO₂ into (bi)carbonates, enabling additional atmospheric CO₂ removal. A key knowledge gap is how alkaline materials affect marine life. This study investigated effects of OAE via sodium hydroxide (NaOH) on a coastal Tasmanian plankton community. Natural communities were enclosed within microcosms assigned to three groups: a control, an unequilibrated treatment (NaOH addition), and an equilibrated treatment (NaOH and sodium bicarbonate (NaHCO₃) addition). The unequilibrated treatment simulates carbonate chemistry changes before atmospheric CO₂ uptake and the equilibrated treatment the changes thereafter. Treatments increased alkalinity by ~25% (+500 μmol · kg⁻¹), theoretically enabling a 21% increase in the marine inorganic carbon sink. Hydroxide-based OAE had minimal effects on the plankton community in the equilibrated treatment, in which CO₂ and pH excursions were small. In the unequilibrated treatment, we observed a slight delay in the phytoplankton bloom, arguably because NaOH addition caused reorganization in the diatom community before the bloom reached its maximum chlorophyll a level. Although the community remained diatom-dominant, community composition was moderately different from the control and equilibrated treatments. The zooplankton community displayed no detectable change except for the invasive Noctiluca scintillans, which became less abundant in the unequilibrated treatment, arguably due to phytoplankton community shifts. We concluded changes in plankton community composition observed were relatively small compared to the rather extreme hydroxide-based alkalinity perturbation and the profound climatic benefit of such a CO₂ sink enhancement.

Since 2011, holopelagic Sargassum has been accumulating in a region of the tropical Atlantic now referred to as the Great Atlantic Sargassum Belt (GASB). Among the hypothesized contributors to these accumulations are the increased inputs of nitrogen (N) and phosphorus (P) in the tropical Atlantic Ocean. Little is known about the effects of N and P additions on Sargassum physiology and its microbiome. We studied the effects of N, P, and NP additions on the growth, photosynthetic efficiency, and microbiome composition of Sargassum fluitans III in a six-day experiment on the Caribbean Island of Curaçao. Sargassum fluitans III took up most nitrate and phosphate within 3 days with respective uptake rates of 0.343 and 0.0399 μmol · g⁻¹ DW · h⁻¹. Fv/Fm decreased in the control after 6 days but remained constant in nutrient treatments. Growth rates did not differ significantly among treatments, but a trend in higher growth rates in the NP treatment was discerned, suggesting a possible NP co-limitation. The relative abundance of epiphytic Cyanobacteria such as Schizothrix and bacteria such as Lentilitoribacter increased under N and P addition, while heterotrophic Rhodobacteraceae decreased in abundance. Microeukaryotic communities responded with varying changes in alpha diversity, possibly steered by increased photosynthesis and growth of S. fluitans III or bacterial interactions. The physiological response to N and P and rapid change of the microbiome demonstrates that the studied S. fluitans III can quickly benefit from increased nutrient concentrations, which might contribute to its growth success in the GASB.

The class Bolidophyceae, which consists of small phytoplankton distributed worldwide, is the sister group of diatoms. This class has contained only one order, the Parmales, until now. In this study, we established a new order Lepidoparmales Kamakura & S.Sato ord. nov. and a new family Lepidoparmaceae Kamakura & S.Sato fam. nov., within the Bolidophyceae, and described Lepidoparma frigida Kamakura & S.Sato gen. et sp. nov. from the Sea of Okhotsk. We conducted a comprehensive comparison of L. frigida with diatoms and other parmaleans through analysis of its molecular phylogeny, morphology, ultrastructure, ontogeny, distribution, and lipid composition. The cell surface of L. frigida is covered with numerous siliceous scales with radial patterns similar to centric diatom valves; this character distinguishes it from other known parmaleans. Intriguingly, its appearance resembles the hypothesized “pre-diatom,” which was proposed to be a precursor to primitive diatoms. The discovery and characterization of L. frigida will provide valuable insights into the evolutionary processes of both diatoms and bolidophytes and shed light on their common ancestor.