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 separat...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.
In their recent paper Kidron et al. (Journal of Phycology, 2025) aimed to demonstrate that the reported extreme differences of up to 25°C between air and rock temperatures measured by Büdel et al. (Journal of Phycology,...In their recent paper Kidron et al. (Journal of Phycology, 2025) aimed to demonstrate that the reported extreme differences of up to 25°C between air and rock temperatures measured by Büdel et al. (Journal of Phycology, 2008) at Mt. Falconer in the Antarctic Taylor Valley, were likely in error. They suggested possible sources of errors that might have led to our modeling of dewfall. By reprogramming our (Hoffmann, 1955) and their (Beysens, 2018) suggested models, we have shown that our calculations regarding climatic data were correct, even with both models. We have provided new climate data from Linnaeus Terrace (Dry Valleys, Antarctica) to support our results, by water-related net photosynthesis of a unicellular (Chroococidiopsis sp.) and a filamentous cyanobacterial strain (Funiculus sociatus). In contrast to the claim of Kidron et al., both cyanobacteria showed positive net photosynthesis well below 1 mm precipitation equivalent water content. We suggest further improved field measurements to strengthen our observation and conclude that reactivation of inactive endolithic cyanobacteria by condensation could be possible but might not be the main source of water.
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,...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 dir...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 · s, 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.
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 p...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.
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...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.
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 soluti...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 numbe...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 CO removal approach for climate change mitigation and can be implemented with various alkaline materials that convert dissolved CO into (bi)carbonates, ena...Ocean alkalinity enhancement (OAE) is an emerging carbon dioxide CO removal approach for climate change mitigation and can be implemented with various alkaline materials that convert dissolved CO into (bi)carbonates, enabling additional atmospheric CO 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 (NaHCO) addition). The unequilibrated treatment simulates carbonate chemistry changes before atmospheric CO uptake and the equilibrated treatment the changes thereafter. Treatments increased alkalinity by ~25% (+500 μmol · kg), 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 CO 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 CO 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...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 DW · h. 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...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.
The genus Symbiochlorum, initially described from a single strain isolated from a coral in the South China Sea, was shown to be a sister lineage of Ignatius within the green algal order Ignatiales. Its significant phylog...The genus Symbiochlorum, initially described from a single strain isolated from a coral in the South China Sea, was shown to be a sister lineage of Ignatius within the green algal order Ignatiales. Its significant phylogenetic divergence from Ignatius raises the possibility of its classification as a new family. To further investigate this hypothesis, we conducted a more elaborate analysis of sequence diversity within the Symbiochlorum clade. We aligned the 18S nuclear ribosomal DNA gene sequences of newly isolated Symbiochlorum culture strains from coral in the South China Sea and environmental sequences from the Great Barrier Reef. Strains isolated from Porites lutea coral colonies exhibited morphological similarities to typical S. hainanense (CCTCC M2018096). Analysis of the 18S nuclear ribosomal DNA gene revealed substantial diversity in both the V4 and V9 regions of the gene, with sequences clustering into two distinct lineages. Lineage 1 (L1), represented solely by environmental sequences from Great Barrier Reef sediment samples, displayed high levels of sequence divergence (2.2%-5.8%), suggesting it consists of multiple species. Lineage 2 (L2) included coral-derived strains and environmental sequences from the South China Sea and the Great Barrier Reef, as well as an ascidian-associated strain from Palau. The significant divergence between L1 and L2 (3.1%-9.1%) suggests they represent different genera. Based on these results, we propose the recognition of the new family Symbiochloraceae within the Ignatiales order.
Ecological stability is central to understanding how disturbances challenge the persistence of populations and communities through time, especially when key species are impacted. The bull kelp Durvillaea incurvata is a f...Ecological stability is central to understanding how disturbances challenge the persistence of populations and communities through time, especially when key species are impacted. The bull kelp Durvillaea incurvata is a foundation, habitat-forming species that provides food and shelter for various species and supports the livelihoods of human communities along the Chilean coast. Harvesting of Durvillaea has raised concerns about the long-term viability of its populations, but the stability responses of Durvillaea to anthropogenic disturbances remain unclear. Here, we conducted a manipulative experiment in which we removed, once, all Durvillaea individuals from two sites in southern Chile to simulate the spatial scale of harvesting and to describe the population resilience and recovery following disturbance. In 1-m plots interspersed in matrices of dense Durvillaea stands, we removed fronds and holdfasts, a practice not typically developed by gatherers, testing an alternative harvesting strategy. For 25 months, we quantified Durvillaea recruitment, holdfast densities, percent cover, frond length and density, biomass, and population size structure. All metrics completely recovered within 5-7 months across sites. The removal of Durvillaea did not have a significant impact on recruitment, which was constant during the experiment. The small spatial scale of the disturbances, the constant recruits supplied by the surrounding bull kelp matrix, and the removal of holdfasts that released settlement substratum allowed for the strong stability responses in these populations. Therefore, harvesting strategies that promote spatial heterogeneity, such as the removal of whole individuals at a small spatial scale, should be prioritized in management schemes of natural seaweed stands.
Microalgae are natural producers of essential nutrients and pigments for both human and animal nutrition as well as medical applications. This study aimed to characterize some microalgae by their taxonomy and biochemical...Microalgae are natural producers of essential nutrients and pigments for both human and animal nutrition as well as medical applications. This study aimed to characterize some microalgae by their taxonomy and biochemical composition. Molecular techniques were used to categorize the microalgal strains into the genera of Chlorococcum, Coccomyxa, and Ochromonas. Subsequently, microalgal growth under laboratory conditions was assessed and the microalgal cells were harvested to determine the pigments, proximate composition, fatty acid, and amino acid profiles. The findings indicated that the cell densities of Coccomyxa sp. and Ochromonas sp. were nearly identical. Additionally, all microalgae exhibited chlorophyll a as the main pigment component, whereas Coccomyxa sp. and Chlorococcum sp. showed significantly highest (p < 0.05) chlorophyll a (7.79 ± 0.07 μg · mL) and chlorophyll b (2.74 ± 0.002 μg · mL), respectively. Significantly higher (p < 0.05) carotenoid and total phycobiliproteins content were found in Ochromonas sp. Furthermore, Coccomyxa sp. was determined to have significantly higher (p < 0.05) protein (31.9% ± 0.46% dry weight) and lipid content (18.2% ± 1.34% dry weight), while the maximum carbohydrate was detected for Ochromonas sp. (29.2% ± 0.1% dry weight). Lastly, essential amino acid (EAA) levels were considerably higher (p < 0.05) in Chlorococcum sp.; however, Coccomyxa sp. produced more polyunsaturated fatty acids (PUFA) in comparison to the other experimental species. The results indicate that the investigated microalgae possess immense potential as multi-nutrient sources and can be optimized for sustainable application in aquaculture, pharmaceuticals, and nutraceutical industries.
Seaweeds can be negatively affected by low salinity, but the negative impacts may be ameliorated by the presence of high nutrient levels from the freshwater inputs. We tested this hypothesis on the eucheumatoids Kappaphy...Seaweeds can be negatively affected by low salinity, but the negative impacts may be ameliorated by the presence of high nutrient levels from the freshwater inputs. We tested this hypothesis on the eucheumatoids Kappaphycus alvarezii, K. striatus, and Eucheuma denticulatum by determining their nutrient uptake, growth, and biochemical responses to experimental treatments of lowering salinity with a consequent increase in nutrient concentrations. Ambient seawater with varying salinity and nutrient concentrations was sourced offshore (O) and nearshore (N) and diluted with nutrient-replete natural spring water to obtain six (6) treatments: O-LN-34, O-MN-30, O-HN-27, N-MN-30, N-HN-27, and N-HN-24 (corresponding to water source-relative nutrient concentration- salinity, where LN = low nutrient; MN = medium nutrient; HN = high nutrient). Nutrient uptake varied among inorganic nutrient species and different eucheumatoid species. All eucheumatoids showed uptake preference for NH regardless of the treatment while NO uptake was generally higher in treatments with higher NO concentration. Growth rates were species-specific but generally higher at lower salinities with higher nutrient concentrations. Total soluble carbohydrate, total protein, and total polyphenol content did not significantly vary among treatments, except for E. denticulatum. These results provide insights into the potential of farming eucheumatoids nearshore with fluctuating salinity provided that the freshwater outflow is nutrient-rich to ameliorate the negative effects of low salt concentration.
Free-living coralline beds are typically composed of rhodoliths, or unattached non-geniculate coralline algae. In 2017, the first beds comprised primarily of free-living geniculate coralline algae, termed articuliths, we...Free-living coralline beds are typically composed of rhodoliths, or unattached non-geniculate coralline algae. In 2017, the first beds comprised primarily of free-living geniculate coralline algae, termed articuliths, were documented in Arraial do Cabo Bay in southeastern Brazil. During routine barcode surveys of the Haida Gwaii, British Columbia, Canada flora, 16 rhodolith-like specimens were collected from a rhodolith bed that DNA sequences assigned to the geniculate taxa Calliarthron tuberculosum and Bossiella sp. 1heteroforma. To our knowledge, articuliths have not been documented outside of Brazil; this discovery thus documents the first instance of northern hemisphere articuliths. Despite disparate gross morphologies to attached conspecific populations, anatomical observations revealed internal anatomies consistent with those of attached forms but with a significant reduction in the number of genicula and increased uniformity in intergenicular shape.