Homothallic, monoicous species of the green alga genus Volvox produce both male and female gametes within a single sexual spheroid. Thus, these taxa are considered strictly inbred. However, the evolution and diversification of such monoicous species have not been studied using molecular data. Volvox sp. Sagami is a homothallic, monoicous alga distinguished from other Volvox species by the morphological characteristics of its zygotes. Nevertheless, this alga has not been formally classified because the sequence of its internal transcribed spacer (ITS) region of nuclear ribosomal DNA is highly similar to that of its sister species, V. ferrisii. To investigate the species distinctness and diversity within Volvox sp. Sagami and V. ferrisii, we examined five single-copy nuclear genes (psbO, atp2, actin1, efl and MID) and the ITS region. These six nuclear DNA fragments were examined in ten culture strains of V. sp. Sagami and ten culture strains of V. ferrisii, originating from various freshwater localities in Japan. The analysis of the five gene sequences revealed a clear distinction between V. sp. Sagami and V. ferrisii. Concatenated sequences of the six nuclear DNA fragments revealed minimal genetic divergence within each species and no evidence of hybridization or gene flow between the two species. This finding potentially represents the typical molecular evolution of homothallic, monoicous species in natural populations. Consequently, Volvox sp. Sagami exhibits a state of reproductive isolation from its sister species, V. ferrisii. Here, Volvox sagami sp. nov. is described.
Scinaia is the second most diverse genus of the order Nemaliales, containing 45 species. While three species of Scinaia are currently recognized in Hawaii, occurring commonly to depths of 10 m, a thorough DNA-based analysis of Hawaiian Scinaia diversity is lacking. Mesophotic ecosystems in the Hawaiian archipelago, occurring from 30 to >150 m depths, are known to harbour high levels of endemism, and numerous new algal species and genera have been discovered in these habitats. Here, we characterize Scinaia specimens collected from the Papah & amacr;naumoku & amacr;kea National Marine Sanctuary in the northwestern Hawaiian Islands and the Main Hawaiian Islands using both morphological and molecular approaches. Through phylogenetic analyses, six distinct lineages of Scinaia were identified, and three of these are described as new species: Scinaia ohulumoaula sp. nov. with long unconstricted segments, S. hekeuliuli sp. nov. with short unconstricted segments and S. uohulualii sp. nov. with large cartilaginous thalli and constricted branches. Of these six Hawaiian species, two are restricted to mesophotic depths (>30 m), two are found in both deep and shallow water reefs and two are observed only in shallow waters. Mitochondrial (a first for the Nemaliales) and plastid genomes were used to further characterize the new species. Plastid genomes were structurally similar to others available for the genus. These data provide additional evidence of highly diverse, distinct and endemic assemblages from mesophotic ecosystems in the Hawaiian archipelago.
Braarudosphaera bigelowii is a marine coccolithophorid characterized by pentagonal calcareous plates called pentaliths. It has been regarded as a species complex comprising multiple species that can be distinguished from each other based on the size of pentaliths and 18S rRNA gene sequences. Chrysochromulina parkeae, a marine haptophyte, was once considered an independent species, but now is known to be a part of the life cycle stages of any one of the species of the B. bigelowii species complex. However, the formal taxonomy of these species complexes has not been reevaluated. This study examined relationships among sizes of cell, pentaliths and organic scales, nuclear 18S rRNA gene sequences, and nifH and 16S rRNA gene sequences of nitroplasts in the B. bigelowii species complex. Our results showed that the size of cells, pentaliths and scales differed among different sequence types, and are useful for classification of Braarudosphaera. The definition of B. bigelowii sensu stricto (s.s.) was emended, and the morphotypes Intermediate Form-A was raised to the species rank as Braarudosphaera okadae sp. nov. The cell and scale sizes of 18S type IV strain were larger than those of B. bigelowii s.s. strains (18S type III) and overlapped to those of C. parkeae holotype. Therefore, 18S type IV and C. parkeae are considered as conspecific, and a new combination, Braarudosphaera parkeae comb. nov. is proposed.
Mat-dwelling coccoid cyanobacteria are diverse and ecologically significant members of marine microbial communities. Despite their global presence, much of their diversity remains undocumented, particularly in tropical coastal environments. In this study, a coccoid cyanobacterial strain, KBR, was isolated from a microbial mat growing on concrete jetty surfaces on Pulau Perhentian Besar, an island in Terengganu, East Malaysia. The strain exhibited morphological features characteristic of the genus Chroococcus, forming spherical to hemispherical cells occurring singly or in dyads. However, 16S rRNA phylogenetic analysis revealed that strain KBR forms a distinct clade within the family Chroococcaceae. It was closely related to Chroococcus turgidus but separate from the core Chroococcus sensu stricto clade, i.e. genera Neochroococcus and Inacoccus. The 16S rRNA gene sequence of strain KBR shared less than 95% identity with type strains of other Chroococcaceae genera. In addition, strain KBR was morphologically distinct, displaying larger cell diameters (20.1-35.8 mu m), olive-green pigmentation, weakly granulated cytoplasm and cell division in a single plane. Secondary structure analysis of the 16S-23S ITS region in the D1-D1 ' helix further supported its taxonomic uniqueness. Based on a polyphasic approach, we propose that strain KBR represents a novel genus and species, Sandococcus viridis gen. et sp. nov. The establishment of this new taxon contributes to ongoing revisions in Chroococcaceae systematics and sheds light on the hidden cyanobacterial diversity of tropical marine ecosystems.
Monostromatic green macroalgal blades, including members of the genus Gayralia, as well as Monostroma, forms the base of coastal ecosystems and are economically important, particularly in East Asia. However, our understanding of their diversity remains incomplete because knowledge of thallus ontogeny, life cycles, and molecular phylogeny is limited. Here, we report a new asexual member of Gayralia. Monostromatic thalli collected from Tateyama, Chiba, Japan, exhibited a monomorphic life cycle via biflagellate zooids. No fertilization was observed between zooids released from any thalli, suggesting that this population primarily consisted of asexual individuals. Thallus ontogeny and morphology differed from those of other reported members of Gayralia. Our molecular phylogeny based on the internal transcribed spacer regions of rDNA suggests that they form a clade with undescribed Gayralia lineages distributed in Japan. Therefore, we proposed Gayralia orientalis sp. nov. for this clade. This study advances the understanding of the diversity, ecology, and application potential of monostromatic green macroalgae.
Prymnesium parvum, a eurytherm and euryhaline haptophyte, has been held responsible for the development of algal blooms leading to fish kills and heavy economic losses for decades. There is increasing evidence of cryptic diversity within this taxon, with three clades delimited by molecular phylogenetics that also produce different toxins. Mass developments of this alga were observed under low to brackish salinities, with temperature conditions spanning a wide range. However, the possibly interactive effects of these two environmental factors upon the growth of diverse strains characterized with respect to their clade memberships have so far been seldom investigated. We assessed the clade membership of four strains originating from three locations, along with their growth in batch cultures under a range of temperature and salinity conditions. Two strains belonging to Clade C, collected from the Mediterranean Sea, generally grew substantially faster than the other pair of strains belonging to Clade B and isolated from the river Oder, Germany. Whereas the freshwater/Clade B strains grew well at the lowest salinities tested, growth rates of the marine/Clade C strains declined starkly in the low salinity range. Contrastingly, high salinity conditions allowed for growth only of the marine/Clade C strains. These results can be interpreted either as differential local adaptations between marine versus freshwater strains, or as clade-specific ecophysiological differences. To decide which of these hypotheses better explains patterns of physiological variability in the P. parvum complex, further studies on strains covering a broader range of habitat - clade membership combinations will be necessary.
The red alga Dipterosiphonia australica is a relatively new endemic species of Rhodomelaceae found in southeastern Australia, growing as part of algal turfs or as an epiphyte on larger algae. Recent findings from family-level diversity surveys have suggested that cryptic diversity may be occurring within this species. We investigated this further using an integrative taxonomic approach that combined DNA sequencing of the rbcL gene with morphological observations, and morphometric analysis. Phylogenetic analyses resolved the morphological specimens of D. australica into two distinct sister clades, which were proposed as two separate candidate species using the ASAP and GMYC species delineation methods. These two molecular entities also have distinct distributions: in Victoria, one is restricted to the eastern coast, while the other is found on the western coast. However, they were morphologically indistinguishable. Based on our findings, we hereby describe a new endemic cryptic species, D. erecta sp. nov. We also provide new molecular and morphological data for D. australica, including morphological features not previously documented for this species, and propose an epitype. This study contributes to our understanding of the taxonomy of the genus Dipterosiphonia and, more broadly, to our knowledge of the species diversity in algal turfs.
Microalgae from ice and under-ice water communities can serve as valuable models for studying how unique physiological adaptations influence the phylogeography of single-celled eukaryotes. Gymnodinium baicalense is a freshwater planktonic dinoflagellate, historically recognized as one of the few freshwater dinoflagellates with a restricted distribution, primarily within the Lake Baikal region. However, we found a similar morphospecies far from this area - in Lake Ilmen - which differs from Lake Baikal in numerous characteristics including age, depth, trophic status, oxygen saturation, transparency, and chemical stability. Genetic analyses, combined with morphological and ecological data revealed the close evolutionary relationships between these freshwater lineages and Gymnodinium corollarium from the Baltic Sea. We propose that the Lake Baikal and Lake Ilmen lineages belong to the same species, though the Baikal lineage due to its remote location has accumulated some unique mutations in its rDNA. A single episode of marine-freshwater transition, with further G. baicalense colonization of various lakes is suggested as the most likely scenario of the species dispersal. This discovery challenges the notion of G. baicalense as an endemic species and prompts to check of under-ice dinoflagellate blooms in other northern freshwater lakes.
The genus Pleodorina comprises green algae with multicellular, spheroidal colonies that represent an early stage of germ-soma differentiation in the evolution of organismal complexity within the volvocine lineage. One species, P. japonica harbours abundant rickettsial endosymbionts ('MIDORIKO') in its cytoplasm. Maintaining Pleodorina cultures requires repeated inoculation of living material, and only one cryopreserved strain, P. californica strain UTEX 198, has been established in public collections. To investigate cryopreservation conditions for other Pleodorina species, we examined immature colonies of four Pleodorina species and compared the effects of two cryoprotectants: N,N-dimethylformamide (DMF) and methanol. After cryopreservation in liquid nitrogen and thawing, we observed >0.6% cell survival (acceptable levels of >0.1% for culture collections) in P. japonica, P. starrii, and P. indica when samples were treated with 6% DMF and subjected to a two-step freezing protocol. However, >0.1% survival was not detected when treated with 3% methanol in all species of Pleodorina. We further confirmed that P. japonica retained inducibility of sexual reproduction and continued to harbour 'MIDORIKO' within the cytoplasm after cryopreservation and thawing.
Increases in Harmful Algal Blooms (HABs) of toxic microalgae represent a growing concern worldwide. Poleward spread of HAB distribution is linked to climate change. Molecular tools permit more rapid and accurate responses, which complement traditional tools, for HAB species identification. Our electrochemical detection method, with a single unlabelled capture probe, represents a vast improvement over earlier methods using a sandwich hybridization method with two probes in that it is 10 times more sensitive. We analysed samples taken twice weekly in July 2022, from two locations in the northwestern Iberian Peninsula within the INTECMAR monitoring system in Galicia (Spain), and single samples from IPMA monitoring points in Porto and Aveiro (Portugal). Gambierdiscus spp. earlier reported offshore, were documented molecularly in coastal waters for the first time. Ostreopsis spp. earlier detected with microscopical and molecular methods, was also documented molecularly. This genus displayed an apparent range expansion in the southwestern Portuguese coasts, and along the northern (Bay of Biscay) and Mediterranean coasts of Spain. To increase species detection levels, 10 L samples were filtered, which is likely the reason why we found molecular signals where none of these cells were detected in the 50 mL settled volumes taken by the monitoring agencies and IEO. Improved calibration curves may revise lower inferred cell numbers because signals were normalized against a no DNA control, which was often high. The present study provides new information on emergent toxin-producing taxa of interest for regional monitoring programmes and their potential expansion in the area.
This study provides a taxonomic evaluation of the bladed Bangiales along the Peruvian coast furthering understanding of the diversity and taxonomy of these seaweeds, focusing on the economically important genera Porphyra and Pyropia. Based on new collections (114 specimens across 1,778 km; 7-17 degrees S), we applied morphological-anatomical and molecular analyses, including species delimitation methods (ABGD and GMYC), to identify three new species. Phylogenetic analyses of rbcL and COI markers, combined with morphological data, confirmed the presence of three Pyropia species: P. orbicularis, P. suborbiculata, and the newly described Pyropia humboldtii sp. nov.; and three Porphyra species: P. acletoi sp. nov. P. tavari sp. nov. and Porphyra sp. CHF (an undescribed genetic species). Pyropia humboldtii sp. nov. with eight haplotypes, exhibited a wide latitudinal distribution from Casma, Ancash (9 degrees S) in Peru to Coquimbo (30 degrees S) in Chile. It displayed considerable frond variability, with colours ranging from light purple to greenish and brownish, and fronds predominantly lanceolate or lobed. The two new Porphyra species showed limited genetic variability: Porphyra acletoi sp. nov. was restricted to the central Peruvian coast (9-11 degrees S), while Porphyra tavari sp. nov. had a distribution range from Malabrigo, La Libertad (7 degrees S) to Pucusana, Lima (12 degrees S). This systematic revision refines our understanding of Bangiales diversity and distribution along the Peruvian coast. It challenges previous morphological identifications by reassigning specimens formerly attributed to Porphyra columbina and P. pseudolanceolata to newly described species: Pyropia humboldtii, Porphyra acletoi, and Porphyra tavari.
Specimens of the freshwater red algal genus Riverina were discovered in a clear-water river in Mauritius, marking the first record of the genus from an Indian Ocean island. Morphological observations and phylogenetic analyses of chloroplast rbcL and nuclear-based 18S rDNA sequences were used to characterize the collection. While the specimens were morphologically similar to known Riverina species, molecular data placed them within a distinct clade sister to R. tahitiensis and R. angolensis. Significant genetic divergence from Tahitian and Philippine lineages confirms that the Mauritian material represents a distinct evolutionary lineage. Consequently, Riverina vaughanii sp. nov. is formally described. This study expands the known biogeographic range of the genus and highlights the cryptic diversity of freshwater red algae in the western Indian Ocean island.
Mutations conferring resistance to lethal conditions impose a physiological cost to organisms. A scarcely explored aspect of this physiological cost is how resistance mutations impact cell division in microorganisms. We explored how a mutation that allows proliferation under lethal sulphide levels in the cyanobacterium Microcystis aeruginosa affects cell division. Two strains of M. aeruginosa were used: the wild-type ancestor, characterized by extreme sensitivity to sulphide, and one experimentally selected that can proliferate under sulphide levels that were lethal for the wild type. Five independent isolates of each strain were cultured under the same conditions. After proliferation, we photographed 20 pairs of recently divided daughter cells and individual cells from each isolate. The vertical diameters of daughter cells and surface area and perimeter of isolated cells were measured. Asymmetry (computed as the absolute value of the difference between the vertical diameters of 15 daughter cells) was significantly higher in the sulphide-resistant strain than in the wild-type. The coefficient of form (an estimate of circularity of the cells' outlines) was also effected in the mutant strain. The resistant strain showed increased asymmetry between daughter cells and anomalous cell morphologies that deviated from spherical. These results indicate that resistance to lethal sulphide concentrations in M. aeruginosa imposes a physiological cost that compromises cell division, resulting in increased daughter cell asymmetry and altered cell morphology. Such morphological alterations constitute a measurable component of the physiological trade-offs associated with resistance mutations in unicellular organisms.
Cryptic algal diversity poses significant challenges for accurate species delimitation, phylogenetic reconstruction, and biogeographic patterns in tropical coastal ecosystems, particularly across Southeast Asian biogeographic barriers. We investigated the phylogeography and genetic connectivity of two cryptic Bostrychia binderi species throughout Southeast Asia, with emphasis on the Thai-Malay Peninsula, using plastid-encoded RUBISCO spacer sequences. Phylogenetic analyses revealed two cryptic species (previously named A and 1A) with contrasting genetic diversity patterns. Species A exhibited seven haplotypes with higher diversity in Andaman Sea populations, while species 1A showed only two haplotypes with slightly higher diversity in Gulf of Thailand populations. Population genetic analyses demonstrated significant but low to moderate genetic differentiation between coasts, indicating the Thai-Malay Peninsula functions as a semi-permeable phylogeographic barrier. Regional analysis across Southeast Asia revealed complex connectivity patterns, with species A showing widespread distribution from Thailand to Papua New Guinea, while several haplotypes exhibited specific endemism in Thailand, Philippines, and Indonesia. Additionally, widespread haplotypes demonstrated exceptional long-distance dispersal across Southeast Asian waters despite regional genetic differentiation. These findings reveal complex interactions between oceanographic processes and historical biogeography, highlighting how molecular approaches can address the challenges posed by cryptic diversity while emphasizing the importance of such insights for marine conservation planning and protected area design.
Diversity of tropical gelidioid algae is often overlooked due to the superficial similarity even between species of different genera. Specimens of Indonesian Ptilophora previously identified as P. scalaramosa were collected on three islands in the Indonesian archipelago and compared to P. scalaramosa specimens collected from the species type locality in Bulusan, the Philippines. An integrative approach utilizing morphological and genetic data demonstrated that the Indonesian specimens represent two species, one herein described as P. legalliae sp. nov. Ptilophora legalliae can be distinguished from P. scalaramosa and other Ptilophora species by this combination of traits: plants fasciculate from rhizomatous holdfast, short alae on the middle part of erect axes, short pinnules, with 2-3 layers of outer cortical cells. Ptilophora legalliae inhabits intertidal to subtidal rocky substrates in Indonesia, while P. scalaramosa occurs consistently on subtidal substrata in the Philippines. Phylogenetic analyses of rbcL places P. legalliae with high support as sister to the subclade of Ptilophora sp. from Indonesia and P. scalaramosa from the Philippines, suggesting that these species likely diverged from a common ancestor in Southeast Asia. This study emphasizes the necessity for molecular approach to decipher the hidden diversity of red algae in Indonesia and adjacent regions.
The allelopathic effects of the diatom Cylindrotheca closterium on the dinoflagellate Prorocentrum donghaiense were investigated under varying nutrient conditions (standard and modified f/2 media) and initial cell densities. Results revealed that C. closterium culture filtrates significantly inhibited the growth of P. donghaiense across all experimental conditions, with stronger effects observed at higher filtrate concentrations and lower initial cell densities. The inhibitory effects were dose-dependent and more pronounced under nutrient-limited conditions, indicating that allelopathy serves as a competitive mechanism regardless of nutrient availability. Interestingly, P. donghaiense filtrates did not affect the growth of C. closterium, underscoring species-specific resistance mechanisms. Biochemical analyses indicated substantial disruptions in P. donghaiense cellular metabolism, including reduced protein synthesis, increased oxidative stress and membrane damage. These findings underscore the ecological role of C. closterium in shaping phytoplankton community dynamics, particularly in nutrient-depleted environments, where allelochemical production may intensify as a competitive strategy. This research provides insights into the mechanism of allelopathic interactions and their potential implications for managing harmful algal blooms in coastal ecosystems.
A planktonic Dolichospermum-like strain FACHB-3676 was isolated from Xionghe Reservoir, an eutrophic drinking water reservoir located in Zaoyang city, Hubei Province, China. Morphologically, this strain closely resembled Dolichospermum smithii, differing in the dimensions of vegetative cells and akinetes, and also resembled members of the genus Sphaerospermopsis, from which it was primarily distinguished by the position of its spherical akinetes. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain FACHB-3676 formed a distinct clade within the family Aphanizomenonaceae, sharing less than 94.5% nucleotide similarity with all described genera. Phylogenetic reconstructions based on rbcLX and nifH gene sequences further supported its placement as a novel lineage within the Aphanizomenonaceae. Additionally, the strain exhibited unique ITS secondary structure features, including the D1-D1' and Box-B helices, reinforcing its taxonomic distinctiveness. Based on this polyphasic approach, the strain is proposed as a new cyanobacterial taxon: Aposphaerospermum hubeiense gen. & sp. nov. Furthermore, PCR amplification and GC/MS analysis confirmed that strain FACHB-3676 produces geosmin, a key compound responsible for earthy-musty odours in freshwater systems.
The unarmoured kareniacean dinoflagellate Gertia stigmatica possesses plastids of a common type among dinoflagellates known as peridinin plastids. However, this alga exhibits an unexpected affinity to the family Kareniaceae, whose members generally possess haptophyte-derived plastids. In this study, a second species of Gertia, Gertia obesa sp. nov. was described. A unialgal culture strain was established from Japan and was observed under LM, SEM and TEM. Its phylogeny was inferred from nuclear-encoded rRNA genes (ITS region and 28S rRNA), and photosynthetic pigments determined by HPLC and its plastid phylogeny by psbC sequence data. This species differs from G. stigmatica by having larger cell length (14-21 mu m vs 6-10 mu m) and the absence of starch-surrounded pyrenoids and an eyespot. A straight furrow of the apical structure complex, characteristic to the Kareniaceae, supported its affinity to this family, in addition to the rRNA gene phylogeny. In microscopic observation and pigment analysis, neither haptophyte-derived plastid nor its traces were detected in G. obesa. Plastids of G. obesa were identical to the conventional peridinin plastids: brown colour, reticulate shape, at a peripheral position in the cell, three-stacked thylakoids, variation and relative amount of photosynthetic pigment, and their phylogenetic position and the molecular evolutionary rate of the psbC gene. These results support that Gertia is a member of the Kareniaceae, with vertically inherited peridinin plastids, without acquiring haptophyte-type plastids.
