Taxonomy and toxicity of Prorocentrum from Perhentian Islands (Malaysia), with a description of a non-toxigenic species Prorocentrum malayense sp. nov. (Dinophyceae)

Refining taxonomic identification of microalgae through molecular and genetic evolution: a case study of Prorocentrum lima and Prorocentrum arenarium

Species delimitation based on lineage definition has become increasingly popular. However, these methods have been limited, especially for species that lack genomic data and are morphologically similar. The trickiest part for the species identification is that the interspecific and intraspecific boundaries are vague. Taking Prorocentrum (Dinophyta) as an example, analysis of cell morphology, growth, and toxin synthesis in both species of P. lima and P. arenarium does not provide a reliable basis for species delineation. However, through phylogenetic and genetic distance analyses of their ITS and LSU sequences, establishment of evolutionary tree based on orthologous gene sequences, and combining the results of automatic barcode gap discovery and Poisson tree processes models, it was sustained that P. arenarium does not belong to the P. lima complex and should be considered as an independent species. Interspecies genetic evolution analysis revealed that P. lima and P. arenarium may contribute to evolutionary direction that favors combating reverse environmental factors. In P. lima, viral invasion may be one of the reasons for its large genome size. In the study, P. lima complex has been selected as an example to enhance the taxonomic identification of microalgae through molecular and genetic evolution, offering valuable insights into refining taxonomic identification and promoting microbial biodiversity research in other species.IMPORTANCEMicroalgae, especially the species known as Prorocentrum, have received significant attention due to their ability to trigger harmful algal blooms and produce toxins. However, the boundaries between species and within species are ambiguous. Clear and comprehensive species delineation indicates that Prorocentrum arenarium should be considered as an independent species, separate from the Prorocentrum lima complex. Improving the classification and identification of microalgae through molecular and genetic evolution will provide reference points for other cryptic species. Prorocentrum occupy multiple ecological niches in marine environments, and studying their evolutionary direction contributes to understanding their ecological adaptations and community succession.

Mapping harmful microalgal species by eDNA monitoring: A large-scale survey across the southwestern South China Sea

A large-scale sampling was undertaken during a research cruise across the South China Sea in August 2016, covering an area of about 100,000 km2 to investigate the molecular diversity and distributions of micro-eukaryotic protists, with a focus on the potentially harmful microalgal (HAB) species along the east coast of Peninsular Malaysia. Environmental DNAs from 30 stations were extracted and DNA metabarcoding targeting the V4 and V9 markers in the 18S rDNA was performed. Many protistan molecular units, including previously unreported HAB taxa, were discovered for the first time in the water. Our findings also revealed interesting spatial distribution patterns, with a marked signal of compositional turnover between latitudinal regimes of water masses, where dinophytes and diatom compositions were among the most strongly enhanced at the fronts, leading to distinct niches. Our results further confirmed the widespread distribution of HAB species, such as the toxigenic Alexandrium tamiyavaichii and Pseudo-nitzschia species, and the fish-killing Margalefidinium polykrikoides and Karlodinium veneficum. The molecular information obtained from this study provides an updated HAB species inventory and a toolset that could facilitate existing HAB monitoring schemes in the region to better inform management decisions.

Taxonomy and abundance of epibenthic Prorocentrum (Dinophyceae) species from the tropical and subtropical Southwest Atlantic Ocean including a review of their global diversity and distribution

In the tropical and subtropical South Atlantic Ocean, studies on the taxonomy and abundance of benthic harmful algae are scarce and the region has been largely under investigated. In this study, morphological descriptions, molecular (LSU rDNA and ITS region) and abundance data of benthic Prorocentrum species from the tropical and subtropical Southwest Atlantic and three oceanic islands are presented. Moreover, a review of global benthic Prorocentrum species richness and distribution is presented. Eleven benthic Prorocentrum species were found in Brazil. Morphological and molecular data on P. borbonicum, P. hoffmannianum, P. lima species complex and P. rhathymum were provided. Prorocentrum panamense, P. cf. caipirignum, P. cf. concavum, P. cf. norrisianum, P. emarginatum/fukuyoi/sculptile complex and two not identified species were observed using scanning electron and/or light microscopy, and morphological descriptions are presented. Prorocentrum lima species complex was found at all investigated sites, in abundances up to 2 × 104 cells g-1 FW at the Northeast Brazil, while maximum abundance of all the remaining species did not exceed 1 × 103 cells g-1 FW. The Fernando de Noronha archipelago can be considered a hotspot of benthic Prorocentrum species diversity, with ten species registered. Data compiled in the literature review shows a clear latitudinal gradient with higher species richness in tropical and subtropical regions relative to temperate areas. It is also evident that there is a bias caused by taxonomic impediment and an uneven sampling effort, with many regions still to be investigated using a combined morphological and molecular effort. Therefore, the current knowledge on the global distribution of benthic Prorocentrum species is likely underestimated.

Variation profile of diarrhetic shellfish toxins and diol esters derivatives of Prorocentrum lima during growth by high-resolution mass spectrometry

Prorocentrum lima is a widely distributed toxigenic benthic dinoflagellate whose production of diarrhetic shellfish toxins threatens the shellfish industry and seafood safety. Current research primarily assesses the difference between free and post-hydrolysis total toxin methods, ignoring the impact of different detection methods on technical accuracy. After removing matrix interference with SPE extraction, a thorough HRMS strategy was created in this study. Alkaline hydrolysis could release the diol esters and played a crucial role in obtaining an accurate assessment of toxin levels, achieving satisfactory recoveries (74.0-147.0%) and repeatability (relative deviation <12.3%). The HRMS approach evaluated toxin profile variation during the growth of three P. lima strains from China. A total of 24 toxin contents varying in composition, content, and a high proportion were detected. The SHG, HN, and 3XS strains had total toxin contents of 23.3 ± 1.74, 19.8 ± 1.25, and 19.5 ± 1.58 pg cell^-1, respectively. The diol esters proportion varied among the strains, with SHG having 58.9-69.9, HN having 75.4-86.5, and 3XS having 91.0-91.7%. The variety of toxins produced by distinct P. lima strains highlighted the significance of this method for appropriately measuring the risks connected with DSTs manufacturing. The proposed approach provides a technical basis for gathering comprehensive and accurate data on the potential risks of P. lima DSTs production, with significant implications for ensuring food safety and preventing harmful toxins from spreading in the marine ecosystem.

Ribosomal DNA Sequence-Based Taxonomy and Antimicrobial Activity of Prorocentrum spp. (Dinophyceae) from Mauritius Coastal Waters, South-West Indian Ocean

Microalgae are unicellular organisms and commonly present in the euphotic zone of marine ecosystems. From the western coast of Mauritius, three strains of Prorocentrum species were isolated from macrophytes and cultured under standard laboratory conditions. Morphologies were examined by light, fluorescence, and scanning electron microscopy, and phylogenetic analyses were based on partial large subunit LSU rDNA (D1-D2) and ITS1-5.8S-ITS2 (ITS) regions. Three Prorocentrum species, including the P. fukuyoi complex, P. rhathymum, and P. lima complex, were identified. The antimicrobial activities were assayed against potential human pathogenic bacterial strains. The highest zone of inhibition was recorded for intracellular and extracellular protein extracts of Prorocentrum rhathymum against Vibrio parahaemolyticus. The polysaccharide extracts of the Prorocentrum fukuyoi complex had a higher zone of inhibition (24 ± 0.4 mm) against MRSA at a minimum concentration of 0.625 μg/mL. The extracts from the three Prorocentrum species had different levels of activity against the pathogens used, and this can be of scientific interest in the search for antibiotics from natural marine sources.

Morphology and phylogeny of Prorocentrum porosum sp. nov. (Dinophyceae): A new benthic toxic dinoflagellate from the Atlantic and Pacific Oceans

A new marine benthic toxic Prorocentrum species is described from the tropical/subtropical regions of the Atlantic (Colombian Caribbean Sea and Northeast Brazil) and Pacific (Southern Japan) oceans. Morphological cell structures were examined using light (LM) and scanning electron (SEM) microscopy. Prorocentrum porosum sp. nov. was characterized by 35.9-50.2 μm long and 25.4-45.7 μm deep cells, covered by broadly ovoid symmetric thecal plates. The surface of both thecal plates is smooth and covered by randomly scattered kidney-shaped pores (n = 102-149), rounder towards the center, absent in the central part, and surrounded by a conspicuous marginal ring of about 69-92 evenly spaced pores. Broad V-shaped periflagellar area exhibiting flagellar and accessory pores. The molecular phylogenetic position of P. porosum sp. nov. was inferred using partial LSU rRNA gene (rDNA) and rDNA ITS sequences. This new species branched with high support in a Prorocentrum clade including P. caipirignum, P. hoffmannianum and P. cf. lima (P. lima morphotype 5 sensuZhang et al., 2015). Pairwise comparison of ITS1 and ITS2 transcripts with these closest relatives revealed the presence of compensatory base changes (CBCs), with the exception of P. cf. lima (P. lima morphotype 5), which only showed in ITS2 a hemi-CBC (HCBC) and two base changes that possibly induce a structural modification. Toxin analyses performed in two Colombian and Brazilian strains in the present study detected the presence of low amounts of okadaic acid.

Six marine thecate Heterocapsa (Dinophyceae) from Malaysia, including the description of three novel species and their cytotoxicity potential

Thirty-four strains of Heterocapsa were established from Malaysian waters and their morphologies were examined by light, scanning, and transmission electron microscopy. Three species, H. bohaiensis, H. huensis, and H. rotundata, and three new species, H. borneoensis sp. nov., H. limii sp. nov., and H. iwatakii sp. nov. were described in this study. The three species were differentiated morphologically by unique characteristics of cell size, shape, displacement of the cingulum, shape and position of nucleus, the number and position of pyrenoids, and body scale ultrastructure. The species delimitations were robustly supported by the molecular data. A light-microscopy-based key to species of Heterocapsa is established, with two major groups, i.e., species with a single pyrenoid, and species with multiple pyrenoids. Bioassays were conducted by exposing Artemia nauplii to Heterocapsa densities of 1-5 × 10⁵ cells mL^-1, and treatments exposed to H. borneoensis showed naupliar mortality, while no naupliar death was observed in the treatments exposed to cells of H. bohaiensis, H. huensis, H. limii, and H. iwatakii. Naupliar death was observed during the initial 24 h for both tested H. borneoensis strains, and mortality rates increased up to 50% after 72-h exposure. This study documented for the first time the diversity and cytotoxic potency of Heterocapsa species from Malaysian waters.

Description of two new species Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov. (Raphidophyceae) from South China Sea, with a report of wild fish mortality

Fisheries damage caused by Chattonella red tide has been recorded in Southeast Asia. Molecular studies have clarified the presence of two species, Chattonella marina complex and Chattonella subsalsa in the region, unlike East Asia that had only C. marina complex. To elucidate the phylogeography of Chattonella in Asia, further phylogenetic and morphological examinations were carried out with 33 additional culture strains, including the strains isolated during a bloom of Chattonella sp. (up to 142 cells mL^-1) that was associated with a wild fish mortality along the northeastern coast of Peninsular Malaysia in 2016, and those from Yellow Sea, where the Chattonella genotypes have not been determined. LSU rDNA and ITS2 trees showed five intrageneric clades in the genus Chattonella, which were clades I and II (C. subsalsa), clade III (C. marina complex) and two new clades, namely clade IV from Thailand and Malaysia, and clade V from Peninsular Malaysia. The positions of the two new clades were different in LSU rDNA and ITS2 trees. LSU rDNA divergences of clades IV and V from the other clades were ≥ 4.01% and ≥ 5.70%, while their ITS2 divergences were ≥ 7.44% and ≥ 16.43%, respectively. Three and five compensatory base changes (CBCs) were observed in the clades IV and V, respectively, when compared to each of their closest clade. Cells from clades IV and V showed similar morphology to C. marina complex and C. subsalsa clade II, including the presence of button-like granules on cell surface and oboe-shaped mucocysts. However, cell size, the number and shape of chloroplasts in Chattonella clades IV and V, and the non-stacked thylakoids penetrated the pyrenoid in C. subsalsa clade II, were distinctive. Based on the diagnostic chloroplast shape, we proposed the designation of clades IV and V to two new species, Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov.

Taxonomy and okadaic acid production of a strain of Prorocentrum lima (Dinophyceae) isolated from the Bay of Bengal, North Indian Ocean

Prorocentrum lima (CSIRCSMCRI005) was isolated from the coastal seawater of Thonithurai, Tamil Nadu, India. Morphology of the isolate was studied using light microscopy (LM) and scanning electron microscopy (SEM) while phylogenetic analyses of the internal transcribed spacer region (ITS1-5.8s-ITS2), 18S rDNA, and large subunit (LSU) rDNA were also carried out. Growth of the isolate was studied, and okadaic acid (OA) production was examined using liquid chromatography with electrospray ionization and quadrupole time of flight mass spectroscopy (LC-ESI-Q-ToF-MS). Morphological features observed including oval cell shape with a broad middle region, narrow anterior and round posterior end, large central pyrenoid with starch sheath, smooth thecal surface, and V-shaped periflagellar area consisting of eight platelets matched with the description of the type species and those reported elsewhere. The ITS, 18S, and LSU sequence phylogenetic analysis revealed that the isolate was closely related to other strains reported from the pacific. The growth rate (μ) was 0.05 div. day^-1. P. lima CSIRCSMCRI005 produced okadaic acid and related esters. The production of free and total OA was 20.12 ± 4.77 and 22.30 fg cell^-1, respectively. The findings of this study contribute useful information concerning the regional risk of diarrheic shellfish poisoning in the North East Indian Ocean and the global distribution and toxic potential of Prorocentrum lima. Further studies on the ecophysiology of this strain will be helpful. This manuscript reports the detailed morphological, phylogenetic, and toxicological characterization of this species from the Bay of Bengal and the North Indian Ocean as a whole.

Over 30 years of HABs in the Philippines and Malaysia: What have we learned?

In the Southeast Asian region, the Philippines and Malaysia are two of the most affected by Harmful Algal Blooms (HABs). Using long-term observations of HAB events, we determined if these are increasing in frequency and duration, and expanding across space in each country. Blooms of Paralytic Shellfish Toxin (PST)-producing species in the Philippines did increase in frequency and duration during the early to mid-1990s, but have stabilized since then. However, the number of sites affected by these blooms continue to expand though at a slower rate than in the 1990s. Furthermore, the type of HABs and causative species have diversified for both toxic blooms and fish kill events. In contrast, Malaysia showed no increasing trend in the frequency of toxic blooms over the past three decades since Pyrodinium bahamense was reported in 1976. However, similar to the Philippines, other PST producers such as Alexandrium minutum and Alexandrium tamiyavanichii have become a concern. No amnesic shellfish poisoning (ASP) has been confirmed in either Philippines or Malaysia thus far, while ciguatera fish poisoning cases are known from the Philippines and Malaysia but the causative organisms remain poorly studied. Since the 1990s and early 2000s, recognition of the distribution of other PST-producing species such as species of Alexandrium and Gymnodinium catenatum in Southeast Asia has grown, though there has been no significant expansion in the known distributions within the last decade. A major more recent problem in the two countries and for Southeast Asia in general are the frequent fish-killing algal blooms of various species such as Prorocentrum cordatum, Margalefidinium polykrikoides, Chattonella spp., and unarmored dinoflagellates (e.g., Karlodinium australe and Takayama sp.). These new sites affected and the increase in types of HABs and causative species could be attributed to various factors such as introduction through mariculture and eutrophication, and partly because of increased scientific awareness. These connections still need to be more concretely investigated. The link to the El Niño Southern Oscillation (ENSO) should also be better understood if we want to discern how climate change plays a role in these patterns of HAB occurrences.

Nontarget Screening and Toxicity Evaluation of Diol Esters of Okadaic Acid and Dinophysistoxins Reveal Intraspecies Difference of Prorocentrum lima

High-resolution mass spectrometry (HRMS) analysis with the assistance of molecular networking was used to investigate intracellular toxin profiles of five Prorocentrum lima (P. lima) strains sampled from the north Yellow Sea and South China Sea. Mice were used as a model species for testing the acute toxicity of intracellular okadaic acid (OA) and dinophysistoxins (DTXs) in free and esterified states. Results showed that OA and DTX1 esterified derivatives were detected in all P. lima samples, accounting for 55%-96% of total toxins in five strains. A total of 24 esters and 1 stereoisomer of DTX1 (35S DTX1) were identified based on molecular networking and MS data analysis, 15 esters of which have been reported first. All P. lima strains displayed specific toxin profiles, and preliminary analysis suggested that toxin profiles of the five P. lima strains might be region-related. Moreover, acute toxicity in mice suggested higher toxicity of esters compared with free toxins, which highlights the importance and urgency of attention to esterified toxins in P. lima.

The first benthic harmful dinoflagellate bloom in China: Morphology and toxicology of Prorocentrum concavum

More frequent events and geographic expansion of benthic harmful algal blooms have been reported in recent years. An unexpected bloom of benthic P. concavum occurred in Xincun Bay, Hainan Island, the South China Sea was monitored in August 2018. Species identification, toxin analysis and toxicity test were conducted in the study. Quantitative study revealed that P. concavum had a high cell density on the surface of substrates and in water column. The bloom forming species was identified based on the morphology and phylogeny. Toxin analysis indicated that there were no detectable DSP toxins either in algae or in shellfish samples. The result of toxicity test revealed that the extracts of P. concavum caused the mortality of brine shrimp larvae (Artemia salina). The results from this study may provide more insight into the rising threats of harmful dinoflagellate blooms to marine benthic ecosystems.

Effects of substratum and depth on benthic harmful dinoflagellate assemblages

Microhabitats influence the distribution and abundance of benthic harmful dinoflagellate (BHAB) species. Currently, much of the information on the relationships between BHABs and microhabitat preferences is based on non-quantitative anecdotal observations, many of which are contradictory. The goal of this study was to better quantify BHAB and microhabitat relationships using a statistically rigorous approach. Between April 2016 to May 2017, a total of 243 artificial substrate samplers were deployed at five locations in the Perhentian Islands, Malaysia while simultaneous photo-quadrat surveys were performed to characterize the benthic substrates present at each sampling site. The screen samplers were retrieved 24 h later and the abundances of five BHAB genera, Gambierdiscus, Ostreopsis, Coolia, Amphidinium, and Prorocentrum were determined. Substrate data were then analyzed using a Bray–Curtis dissimilarity matrix to statistically identify distinct microhabitat types. Although BHABs were associated with a variety of biotic and abiotic substrates, the results of this study demonstrated differing degrees of microhabitat preference. Analysis of the survey results using canonical correspondence analysis explained 70.5% (horizontal first axis) and 21.6% (vertical second axis) of the constrained variation in the distribution of various genera among microhabitat types. Prorocentrum and Coolia appear to have the greatest range being broadly distributed among a wide variety of microhabitats. Amphidinium was always found in low abundances and was widely distributed among microhabitats dominated by hard coral, turf algae, sand and silt, and fleshy algae and reached the highest abundances there. Gambierdiscus and Ostreopsis had more restricted distributions. Gambierdiscus were found preferentially associated with turf algae, hard coral and, to a lesser extent, fleshy macroalgae microhabitats. Ostreopsis, almost always more abundant than Gambierdiscus, preferred the same microhabitats as Gambierdiscus and were found in microbial mats as well. With similar habitat preferences Ostreopsis may serve as an indicator organism for the presence of Gambierdiscus. This study provides insight into how BHAB-specific microhabitat preferences can affect toxicity risks.

Abundance of the benthic dinoflagellate Prorocentrum and the diversity, distribution, and diarrhetic shellfish toxin production of Prorocentrum lima complex and P. caipirignum in Japan

In the present study, the abundance of Prorocentrum and the molecular phylogeny, distribution, and DST production of P. lima complex and P. caipirignum in Japan were investigated. First, the cell densities of Prorocentrum were assessed from the temperate to subtropical zones in Japan between 2014 and 2018. The cell density in the subtropical zone [19.0 ± 40.2 cells/g wet weight (ww) algae] was significantly higher than that in the temperate zone (1.4 ± 3.4 cells/g ww algae). A total of 244 clonal strains were established from the temperate and subtropical zones. Phylogenetic analyses based on the large-subunit ribosomal DNA D1/D2 revealed that the strains were separated into four species/species complex/phylotypes (P. lima complex, P. caipirignum, and new phylotypes Prorocentrum spp. types 1 and 2). The strains of P. lima complex could be separated into two clades (1 and 3). Furthermore, the strains of clades 1 and 3 could be separated into nine subclades (1a, 1c, 1d, 1e, 1f, 1g, 1h, 1i, and 1j) and three subclades (3a, 3b, and 3c), respectively. The strains of P. caipirignum were separated into two subclades (b and e). Each phylotype/subclade showed a unique distribution pattern in Japan: P. lima complex subclades 1a, 1c, and 3a and P. caipirignum subclades b and e were widespread from the temperate to subtropical zones. On the other hand, P. lima complex subclades 1e and 1i were restricted to the temperate zone, and P. lima complex subclades 1d, 1f, 1g, 1h, 1j, 3b, and 3c and Prorocentrum spp. types 1 and 2 were restricted to the subtropical zone. Furthermore, the DST production of the 243 clonal strains was assessed by LC/MS/MS analysis. The results revealed that all strains produced okadaic acid (OA) and that the OA contents of P. lima complex subclades 1d and 1f, P. caipirignum subclades b and e, and Prorocentrum sp. type 2 tended to be higher than those of the other subclades. While P. lima complex subclades 1a, 1e, 1f, and 1i produced DTX1, the other phylotype/subclades produced either no or low quantities of DTX1. A strain of P. lima complex subclade 1e showed the highest OA and DTX1 contents (55.27 and 70.73 pg/cell, respectively) in the world. These results suggest that there are potential risks for DST accumulation in benthic animals in Japan.

Morphology and Phylogenetics of Benthic Prorocentrum Species (Dinophyceae) from Tropical Northwestern Australia

Approximately 70 species of Prorocentrum are known, of which around 30 species are associated with benthic habitats. Some produce okadaic acid (OA), dinophysistoxin (DTX) and their derivatives, which are involved in diarrhetic shellfish poisoning. In this study, we isolated and characterized Prorocentrum concavum and P. malayense from Broome in north Western Australia using light and scanning electron microscopy as well as molecular sequences of large subunit regions of ribosomal DNA, marking the first record of these species from Australian waters. The morphology of the motile cells of P. malayense was similar to P. concavum in the light microscopy, but differed by the smooth thecal surface, the pore pattern and the production of mucous stalk-like structures and a hyaline sheath around the non-motile cells. P. malayense could also be differentiated from other closely related species, P. leve and P. foraminosum, despite the similarity in thecal surface and pore pattern, by its platelet formula and morphologies. We tested the production of OA and DTXs from both species, but found that they did not produce detectable levels of these toxins in the given culturing conditions. This study aids in establishing more effective monitoring of potential harmful algal taxa in Australian waters for aquaculture and recreational purposes.