The toxic dinoflagellate Karenia mikimotoi has been well‐known for causing large‐scale and dense harmful algal blooms (HABs) in coastal waters worldwide and serious economic loss in aquaculture and ...fisheries and other adverse effects on marine ecosystems. Whether K. mikimotoi forms resting cysts has been a puzzling issue regarding to the mechanisms of bloom initiation and geographic expansion of this species. We provide morphological and molecular confirmation of sexually produced thin‐walled resting cysts by K. mikimotoi based on observations of laboratory cultures and their direct detection in marine sediments. Light and scanning electron microscopy evidences for sexual reproduction include attraction and pairing of gametes, gamete fusion, formation of planozygote and thin‐walled cyst, and the documentation of the thin‐walled cyst germination processes. Evidence for cysts in marine sediments was in three aspects: positive PCR detection of cysts using species‐specific primers in the DNA extracted from whole sediments; fluorescence in situ hybridization detection of cysts using FISH probes; and single‐cell PCR sequencing for cysts positively labeled with FISH probes. The existence of sexually produced, thin‐walled resting cysts by K. mikimotoi provides a possible mechanism accounting for the initiation of annually recurring blooms at certain regions and global expansion of the species during the past decades.
In numerous studies, researchers have explored the interactions between fungi and their hosting biota in terrestrial systems, while much less attention has been paid to the counterpart interactions ...in aquatic, and particularly marine, ecosystems. Despite the growing recognition of the potential functions of fungi in structuring phytoplankton communities, the current insights were mostly derived from phytoplankton hosts, such as diatoms, green microalgae, and cyanobacteria. Dinoflagellates are the second most abundant group of phytoplankton in coastal marine ecosystems, and they are notorious for causing harmful algal blooms (HABs). In this study, we used high-throughput amplicon sequencing to capture global snapshots of specific fungal assemblages associated with laboratory-cultured marine dinoflagellate. We investigated a total of 13 clonal cultures of the dinoflagellate
that were previously isolated from 5 geographic origins and have been maintained in our laboratory from several months to more than 14 years. The total recovered fungal microbiome, which consisted of 349 ASVs (amplicon sequencing variants, sequences clustered at a 100% sequence identity), could be assigned to 4 phyla, 18 classes, 37 orders, 65 families, 97 genera, and 131 species. The fungal consortium displayed high diversity and was dominated by filamentous fungi and ascomycetous and basidiomycetous yeasts. A core set of three genera among all the detected fungi was constitutively present in the
strains isolated from geographically distant regions, with the top two most abundant genera,
and
, capable of using hydrocarbons as the sole or major source of carbon and energy. In addition, fungal taxa previously documented as endophytes in other hosts were also found in all tested strains of
. Because host-endophyte interactions are highly variable and strongly case-dependent, these fungal taxa were not necessarily genuine endosymbionts of
; instead, it raised the possibility that dinoflagellates could potentially serve as an alternative ecological niche for the colonization of fungal endophytes. Our findings lay the foundation for further investigations into the potential roles or functions of fungi in the regulation of the growth dynamics and HABs of marine dinoflagellates in the field.
Many studies have demonstrated that some macroalgae (including the widely cultivated red alga
Gracilaria lemaneiformis
) can inhibit the growth of microalgae via allelopathy and resource competition, ...with the former as the major contributor. However, little is known currently about whether or not and how microalgae react as a feedback to the inhibitory effects or, more generally, the interactions between seaweed and microalgae in their co-culturing system. Here, we report a laboratory-based study on the interactions between the seaweed
Gracilaria lemaneiformis
and the common harmful algal blooms (HABs)-forming dinoflagellate
Akashiwo sanguinea
. We found that while both the fresh thalli of
G. lemaneiformis
and the extracts of fresh and dried
G. lemaneiformis
could significantly inhibit the growth of
A. sanguinea
, the dead cells of
A. sanguinea
“revenged”
G. lemaneiformis
via promoting the growth of bacteria and consequently slowed the growth of
G. lemaneiformis
, which was evidenced by the lowered pH, slowed nutrients consumption in the cultures, the elevated counts of bacteria, and the reduced biomass of
G. lemaneiformis
. Collectively, our results showed that while
G. lemaneiformis
could inhibit the growth of microalgae with allelopathy as a major contributor, the death of allelopathy-affected microalgae could promote bacterial growth, which sequentially inhibits the growth of
G. lemaneiformis
as a feedback.
Identification of a core microbiome (a group of taxa commonly present and consistently abundant in most samples of host populations) is important to capture the key microbes closely associated with a ...host population, as this process may potentially contribute to further revealing their spatial distribution, temporal stability, ecological influence, and even impacts on their host’s functions and fitness. The naked dinoflagellate
Karlodinium veneficum
is a cosmopolitan and toxic species, which is also notorious in forming harmful algal blooms (HABs) and causing massive fish-kills. Here we reported the core microbiome tightly associated with 19 strains of
K. veneficum
that were originally isolated from 6 geographic locations along the coast of China and from an estuary of Chesapeake Bay, United States, and have been maintained in the laboratory for several months to over 14 years. Using high-throughput metabarcoding of the partial 16S rRNA gene amplicons, a total of 1,417 prokaryotic features were detected in the entire bacterial microbiome, which were assigned to 17 phyla, 35 classes, 90 orders, 273 families, and 716 genera. Although the bacterial communities associated with
K. veneficum
cultures displayed heterogeneity in feature (sequences clustered at 100% sequence similarity) composition among strains, a core set of 6 genera were found persistent in their phycospheres, which could contribute up to 74.54% of the whole bacterial microbiome. Three γ-proteobacteria members of the “core,” namely,
Alteromonas
,
Marinobacter
, and
Methylophaga
, were the predominant core genera and made up 83.25% of the core bacterial microbiome. The other 3 core genera,
Alcanivorax
,
Thalassospira
, and
Ponticoccus
, are reported to preferably utilize hydrocarbons as sole or major source of carbon and energy, and two of which (
Alcanivorax
and
Ponticoccus
) are recognized as obligate hydrocarbonoclastic bacteria (OHCB). Since OHCB generally present in extremely low abundance in marine water and elevate their abundance mostly in petroleum-impacted water, our detection in
K. veneficum
cultures suggests that the occurrence of obligate and generalist hydrocarbon-degrading bacteria living with dinoflagellates may be more frequent in nature. Our work identified a core microbiome with stable association with the harmful alga
K. veneficum
and opened a window for further characterization of the physiological mechanisms and ecological implications for the dinoflagellate-bacteria association.
"It takes a village to finish (marine) science these days" Paraphrased from Curtis Huttenhower (the Human Microbiome project) The rapidity and complexity of climate change and its potential effects ...on ocean biota are challenging how ocean scientists conduct research. One way in which we can begin to better tackle these challenges is to conduct community-wide scientific studies. This study provides physiological datasets fundamental to understanding functional responses of phytoplankton growth rates to temperature. While physiological experiments are not new, our experiments were conducted in many laboratories using agreed upon protocols and 25 strains of eukaryotic and prokaryotic phytoplankton isolated across a wide range of marine environments from polar to tropical, and from nearshore waters to the open ocean. This community-wide approach provides both comprehensive and internally consistent datasets produced over considerably shorter time scales than conventional individual and often uncoordinated lab efforts. Such datasets can be used to parameterise global ocean model projections of environmental change and to provide initial insights into the magnitude of regional biogeographic change in ocean biota in the coming decades. Here, we compare our datasets with a compilation of literature data on phytoplankton growth responses to temperature. A comparison with prior published data suggests that the optimal temperatures of individual species and, to a lesser degree, thermal niches were similar across studies. However, a comparison of the maximum growth rate across studies revealed significant departures between this and previously collected datasets, which may be due to differences in the cultured isolates, temporal changes in the clonal isolates in cultures, and/or differences in culture conditions. Such methodological differences mean that using particular trait measurements from the prior literature might introduce unknown errors and bias into modelling projections. Using our community-wide approach we can reduce such protocol-driven variability in culture studies, and can begin to address more complex issues such as the effect of multiple environmental drivers on ocean biota.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In order to investigate the effects of various nitrogen (ammonium) concentrations on the epibiotic bacterial community associated with Oocystis borgei, a metabarcoding sequencing method was employed. ...The 16S rDNA sequencing and bioinformatic analysis were conducted on cultures of O. borgei that were grown on four different nitrogen element concentrations (2.5, 10, 50, and 100 mg/L), and the differences in the epibiotic bacterial community and functions of O. borgei among different nitrogen concentrations were compared. The results showed that the chlorophyll a content of O. borgei increased with increasing nitrogen concentrations. A total of 43 operational taxonomic units (OTUs) were obtained from the four groups, which were categorized into 7 phyla, 9 classes, 18 orders, 21 families, and 26 genera. Winogradskyella was the dominant genus in the groups with 2.5 and 100 mg/L nitrogen, while Marinobacter and Winogradskyella were relatively abundant in the groups with 50 and 100 mg/L nitrogen. Functional analysis using PICRUST2 showed that the three most abundant gene functions were carbohydrate metabolism, amino acid transport and metabolism, ribosomal structure and biogenesis, and energy production and conversion. BugBase phenotypic analysis revealed that there were no significant differences in phenotypes between the groups with 2.5 and 10 mg/L nitrogen, while the group with 50 mg/L nitrogen exhibited higher abundance in aerobicity, biofilm formation, mobile genetic elements, and stress tolerance phenotypes. Most of the bacteria in this work belonged to the aerobic types. A redundancy analysis (RDA) of environmental factors demonstrated that nitrogen concentration showed a positive correlation with species changes in the groups with 10 and 50 mg/L nitrogen; chlorophyll a exhibited a positive correlation with species changes in the groups with 50 and 100 mg/L nitrogen. Nitrogen concentration significantly influenced the epibiotic bacterial community associated with O. borgei, leading to changes in dominant species and community structure. This study provides important references for understanding the functional characteristics of the epiphytic microbial community of O. borgei and the exploration of specific microorganisms.
The ever-increasing applications of metabarcoding analyses for environmental samples demand a well-designed assessment of the stability of DNA and RNA contained in cells that are deposited or buried ...in marine sediments. We thus conducted a qPCR quantification of the DNA and RNA in the vegetative cells of three microalgae entrapped in facsimile marine sediments and found that >90% of DNA and up to 99% of RNA for all microalgal species were degraded within 60 days at 4 °C. A further examination of the potential interference of the relic DNA of the vegetative cells with resting cyst detection in sediments was performed via a metabarcoding analysis in artificial marine sediments spiked with the vegetative cells of two Kareniaceae dinoflagellates and the resting cysts of another three dinoflagellates. The results demonstrated a dramatic decrease in the relative abundances of the two Kareniaceae dinoflagellates in 120 days, while those of the three resting cysts increased dramatically. Together, our results suggest that a positive detection of microalgae via metabarcoding analysis in DNA or RNA extracted from marine sediments strongly indicates the presence of intact or viable cysts or spores due to the rapid decay of relic DNA/RNA. This study provides a solid basis for the data interpretation of metabarcoding surveys, particularly in resting cyst detection.
Alexandrium pacificum
(
A. pacificum
) is a typical paralytic shellfish poisonous dinoflagellate. Harmful algal blooms (HABs) caused by this species can bring serious environmental problems and ...economic losses to the aquaculture industry. In this study, transcriptome sequencing and analyses were performed on the neural tissue of
Litopenaeus vannamei
(
L. vannamei
) after acute exposure to
A. pacificum
disrupted solution for 72 h, and differentially expressed genes (DEGs) were identified. The results showed that, compared with the control samples, 300 DEGs were identified in the experimental group, of which 194 were up-regulated, and 106 down-regulated. The gene ontology (GO) functional enrichment analysis showed that DEGs were significantly enriched in the cortical cytoskeleton organization, troponin complex, amylo-alpha-1,6-glucosidase and thymidine phosphorylase. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis found that DEGs were mainly enriched in the oxidative phosphorylation process, intercellular tight junctions and mitophagy. The results showed that the proteoglycans, signaling pathways, and various metabolic processes that regulate cell proliferation, differentiation, and apoptosis all played an essential role in the response of
L. vannamei
to
A. pacificum
toxins.
Energetic metabolism is essential in maintaining the viability of all organisms. Resting cysts play important roles in the ecology of dinoflagellates, particularly for harmful algal blooms ...(HABs)-causative species. However, the energetic metabolism underlying the germination potency maintenance of resting cysts of dinoflagellate have been extremely scarce in studies from physiological and, particularly, molecular perspectives. Therefore, we used the cosmopolitan
as a representative of HABs-forming and cyst-producing dinoflagellates in this work to obtain novel insights into the molecular mechanisms, regulating the energetic metabolism in dinoflagellate resting cysts, under different physical condition. As the starting step, we established a cDNA subtractive library via suppression subtractive hybridization (SSH) technology, from which we screened an incomplete sequence for the
subunit of ATP synthase gene (
), a key indicator for the status of cell's energetic metabolism. The full-length cDNA of
gene from
(
) was then obtained via rapid amplification of cDNA ends (RACE) (Accession: MZ343333). Our real-time qPCR detections, in vegetative cells and resting cysts treated with different physical conditions, revealed that (1) the expression of
in resting cysts was generally much lower than that in vegetative cells, and (2) the
expressions in the resting cysts under darkness, lowered temperature, and anoxia, and during an extended duration of dormancy, were significantly lower than that in cysts under the condition normally used for culture-maintaining (a 12 h light:12 h dark cycle, 21 °C, aerobic, and newly harvested). Our detections of the viability (via Neutral Red staining) and cellular ATP content of resting cysts, at the conditions corresponding to the abovementioned treatments, showed that both the viability and ATP content decreased rapidly within 12 h and then maintained at low levels within the 4-day experimentation under all the three conditions applied (4 °C, darkness, and anoxia), which are well in accordance with the measurements of the transcription of
. These results demonstrated that the energy consumption of resting cysts reaches a low, but somehow stable, level within a short time period and is lower at low temperature, darkness, and anoxia than that at ambient temperature. Our work provides an important basis for explaining that resting cysts survive long-term darkness and low temperature in marine sediments from molecular and physiological levels.
Due to the vital importance of resting cysts in the biology and ecology of many dinoflagellates, a transcriptomic investigation on
was conducted with the aim to reveal the molecular processes and ...relevant functional genes regulating encystment and dormancy in dinoflagellates. We identified via RNA-seq 3,874 (out of 166,575) differentially expressed genes (DEGs) between resting cysts and vegetative cells; a pause of photosynthesis (confirmed via direct measurement of photosynthetic efficiency); an active catabolism including β-oxidation, glycolysis, glyoxylate pathway, and TCA in resting cysts (tested via measurements of respiration rate); 12 DEGs encoding meiotic recombination proteins and members of MEI2-like family potentially involved in sexual reproduction and encystment; elevated expressions in genes encoding enzymes responding to pathogens (chitin deacetylase) and ROS stress in cysts; and 134 unigenes specifically expressed in cysts. We paid particular attention to genes pertaining to phytohormone signaling and identified 4 key genes regulating abscisic acid (ABA) biosynthesis and catabolism, with further characterization based on their full-length cDNA obtained via RACE-PCR. The qPCR results demonstrated elevated biosynthesis and repressed catabolism of ABA during the courses of encystment and cyst dormancy, which was significantly enhanced by lower temperature (4 ± 1°C) and darkness. Direct measurements of ABA using UHPLC-MS/MS and ELISA in vegetative cells and cysts both fully supported qPCR results. These results collectively suggest a vital role of ABA in regulating encystment and maintenance of dormancy, akin to its function in seed dormancy of higher plants. Our results provided a critical advancement in understanding molecular processes in resting cysts of dinoflagellates.
PDF
