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1.
Nat Commun ; 10(1): 4234, 2019 09 17.
Artigo em Inglês | MEDLINE | ID: mdl-31530807

RESUMO

Phytoplankton account for nearly half of global primary productivity and strongly affect the global carbon cycle, yet little is known about the forces that drive the evolution of these keystone microscopic organisms. Here we combine morphometric data from the fossil record of the ubiquitous coccolithophore genus Gephyrocapsa with genomic analyses of extant species to assess the genetic processes underlying Pleistocene palaeontological patterns. We demonstrate that all modern diversity in Gephyrocapsa (including Emiliania huxleyi) originated in a rapid species radiation during the last 0.6 Ma, coincident with the latest of the three pulses of Gephyrocapsa diversification and extinction documented in the fossil record. Our evolutionary genetic analyses indicate that new species in this genus have formed in sympatry or parapatry, with occasional hybridisation between species. This sheds light on the mode of speciation during evolutionary radiation of marine phytoplankton and provides a model of how new plankton species form.


Assuntos
Evolução Molecular , Haptófitas/genética , Fitoplâncton/genética , Variação Genética , Genoma , Haptófitas/classificação , Biologia Marinha , Filogenia , Fitoplâncton/classificação
2.
Mar Pollut Bull ; 146: 355-365, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31426168

RESUMO

Human-induced eutrophication of coastal water may be a major threat to aquatic life. Here, we investigated the effects of N-rich well amelioration brines (WAB) on coastal phytoplankton population's habitat in the surface oligotrophic waters of the southeastern Mediterranean Sea (SEM). To this end, we added WAB (2 concentrations) to mesocosms (1-m3 bags) to surface SEM water during summer and winter, where changes in phytoplankton biomass, activity and diversity was monitored daily for 8 days. Our results demonstrate that WAB addition triggered a phytoplankton bloom, resulting in elevated algal biomass (maximal +780%), increased primary production rates (maximal +675%) and a decrease in eukaryotic algal α-diversity (ca. -20%). Among the species that bloomed following WAB amendments, we found the potentially toxic dinoflagellate Karlodinium venificum. This study adds valuable perspective to the effect of nutrients discharged into nutrient limited SEM coastal waters, and in particular of N-derived WAB.


Assuntos
Nitrogênio/metabolismo , Fitoplâncton/fisiologia , Água do Mar/química , Biodiversidade , Biomassa , Clorofila A/metabolismo , Cianobactérias/fisiologia , Ecossistema , Eucariotos/fisiologia , Eutrofização , Mar Mediterrâneo , Fitoplâncton/genética , RNA Ribossômico 18S , Estações do Ano
3.
Nat Microbiol ; 4(10): 1706-1715, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31332382

RESUMO

In the surface ocean, phytoplankton transform inorganic substrates into organic matter that fuels the activity of heterotrophic microorganisms, creating intricate metabolic networks that determine the extent of carbon recycling and storage in the ocean. Yet, the diversity of organic molecules and interacting organisms has hindered detection of specific relationships that mediate this large flux of energy and matter. Here, we show that a tightly coupled microbial network based on organic sulfur compounds (sulfonates) exists among key lineages of eukaryotic phytoplankton producers and heterotrophic bacterial consumers in the North Pacific Subtropical Gyre. We find that cultured eukaryotic phytoplankton taxa produce sulfonates, often at millimolar internal concentrations. These same phytoplankton-derived sulfonates support growth requirements of an open-ocean isolate of the SAR11 clade, the most abundant group of marine heterotrophic bacteria. Expression of putative sulfonate biosynthesis genes and sulfonate abundances in natural plankton communities over the diel cycle link sulfonate production to light availability. Contemporaneous expression of sulfonate catabolism genes in heterotrophic bacteria highlights active cycling of sulfonates in situ. Our study provides evidence that sulfonates serve as an ecologically important currency for nutrient and energy exchange between microbial autotrophs and heterotrophs, highlighting the importance of organic sulfur compounds in regulating ecosystem function.


Assuntos
Bactérias/metabolismo , Eucariotos/metabolismo , Consórcios Microbianos , Fitoplâncton/metabolismo , Água do Mar/microbiologia , Ácidos Sulfônicos/metabolismo , Processos Autotróficos , Bactérias/classificação , Bactérias/genética , Bactérias/isolamento & purificação , Ritmo Circadiano , Eucariotos/classificação , Eucariotos/genética , Eucariotos/isolamento & purificação , Processos Heterotróficos , Luz , Redes e Vias Metabólicas/genética , Oceano Pacífico , Fitoplâncton/classificação , Fitoplâncton/genética , Água do Mar/química , Ácidos Sulfônicos/química
4.
J Appl Microbiol ; 127(5): 1291-1304, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30970168

RESUMO

Whole-cell bioreporters are genetically modified micro-organisms designed to sense bioavailable forms of nutrients or toxic compounds in aquatic systems. As they represent the most promising cost-efficient tools available for such purpose, engineering and use of bioreporters is rapidly growing in association with wide applicability. Bioreporters are urgently needed to determine phytoplankton iron (Fe) limitation, which has been reported in up to 30% of the ocean, with consequences affecting Earth's global carbon cycle and climate. This study presents a critical evaluation and optimization of the only Cyanobacteria bioreporter available to sense Fe limitation in marine systems (Synechococcus sp. PCC7002). The nonmonotonic biphasic dose-response curve between the bioreporters' signal and Fe bioavailability impairs an appropriate data interpretation, highlighting the need for new carefully designed bioreporters. Here, limitations under low Fe concentrations were related to cellular energy stress, nonlinear expression of the targeted promoter and siderophore expression. Furthermore, we provide critical standard criteria for the development of new Fe bioreporters. Finally, based on gene expression data under a range of marine Fe concentrations, we propose novel sensor genes for the development of new Cyanobacteria Fe bioreporters for distinct marine regions.


Assuntos
Ferro/metabolismo , Fitoplâncton/metabolismo , Synechococcus/metabolismo , Disponibilidade Biológica , Biomarcadores Ambientais/genética , Regulação Bacteriana da Expressão Gênica , Ferro/análise , Oceanos e Mares , Fitoplâncton/genética , Regiões Promotoras Genéticas , Água do Mar/química , Água do Mar/microbiologia , Sideróforos/genética , Synechococcus/genética
5.
Genome Biol Evol ; 11(4): 1275-1292, 2019 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-30937436

RESUMO

The tiny green algae belonging to the Chloropicophyceae play a key role in marine phytoplankton communities; this newly erected class of prasinophytes comprises two genera (Chloropicon and Chloroparvula) containing each several species. We sequenced the plastomes and mitogenomes of eight Chloropicon and five Chloroparvula species to better delineate the phylogenetic affinities of these taxa and to infer the suite of changes that their organelle genomes sustained during evolution. The relationships resolved in organelle-based phylogenomic trees were essentially congruent with previously reported rRNA trees, and similar evolutionary trends but distinct dynamics were identified for the plastome and mitogenome. Although the plastome sustained considerable changes in gene content and order at the time the two genera split, subsequently it remained stable and maintained a very small size. The mitogenome, however, was remodeled more gradually and showed more fluctuation in size, mainly as a result of expansions/contractions of intergenic regions. Remarkably, the plastome and mitogenome lost a common set of three tRNA genes, with the trnI(cau) and trnL(uaa) losses being accompanied with important variations in codon usage. Unexpectedly, despite the disappearance of trnI(cau) from the plastome in the Chloroparvula lineage, AUA codons (the codons recognized by this gene product) were detected in certain plastid genes. By comparing the sequences of plastid protein-coding genes from chloropicophycean and phylogenetically diverse chlorophyte algae with those of the corresponding predicted proteins, we discovered that the AUA codon was reassigned from isoleucine to methionine in Chloroparvula. This noncanonical genetic code has not previously been uncovered in plastids.


Assuntos
Clorófitas/genética , Genoma Mitocondrial , Genomas de Plastídeos , Filogenia , Fitoplâncton/genética , Sequência de Bases
6.
J Microbiol ; 57(4): 252-262, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30929228

RESUMO

Phytoplankton and bacterioplankton play a key role in carbon cycling of aquatic ecosystems. In this study, we found that co-occurrence patterns between different types of phytoplankton, bacterioplankton, and environmental parameters in Lake Baikal during spring were different over the course of three consecutive years. The composition of phytoplankton and bacterial communities was investigated using microscopy and 16S rRNA gene pyrosequencing, respectively. Non-metric multidimensional scaling (NMDS) revealed a relationship between the structure of phytoplankton and bacterial communities and temperature, location, and sampling year. Associations of bacteria with diatoms, green microalgae, chrysophyte, and cryptophyte were identified using microscopy. Cluster analysis revealed similar correlation patterns between phytoplankton abundance, number of attached bacteria, ratio of bacteria per phytoplankton cell and environmental parameters. Positive and negative correlations between different species of phytoplankton, heterotrophic bacteria and environmental parameters may indicate mutualistic or competitive relationships between microorganisms and their preferences to the environment.


Assuntos
Organismos Aquáticos/isolamento & purificação , Bactérias/isolamento & purificação , Lagos/microbiologia , Lagos/parasitologia , Fitoplâncton/isolamento & purificação , Organismos Aquáticos/classificação , Organismos Aquáticos/genética , Bactérias/classificação , Bactérias/genética , Ecossistema , Lagos/química , Filogenia , Fitoplâncton/classificação , Fitoplâncton/genética , Estações do Ano , Temperatura Ambiente
7.
Microb Ecol ; 78(3): 603-617, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30729265

RESUMO

Lake Dziani Dzaha (Mayotte Island, Indian Ocean) is a tropical thalassohaline lake which geochemical and biological conditions make it a unique aquatic ecosystem considered as a modern analogue of Precambrian environments. In the present study, we focused on the diversity of phytoplanktonic communities, which produce very high and stable biomass (mean2014-2015 = 652 ± 179 µg chlorophyll a L-1). As predicted by classical community ecology paradigms, and as observed in similar environments, a single species is expected to dominate the phytoplanktonic communities. To test this hypothesis, we sampled water column in the deepest part of the lake (18 m) during rainy and dry seasons for two consecutive years. Phytoplanktonic communities were characterized using a combination of metagenomic, microscopy-based and flow cytometry approaches, and we used statistical modeling to identify the environmental factors determining the abundance of dominant organisms. As hypothesized, the overall diversity of the phytoplanktonic communities was very low (15 OTUs), but we observed a co-dominance of two, and not only one, OTUs, viz., Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta). We observed a decrease in the abundance of these co-dominant taxa along the depth profile and identified the adverse environmental factors driving this decline. The functional traits measured on isolated strains of these two taxa (i.e., size, pigment composition, and concentration) are then compared and discussed to explain their capacity to cope with the extreme environmental conditions encountered in the aphotic, anoxic, and sulfidic layers of the water column of Lake Dziani Dzaha.


Assuntos
Clorófitas/crescimento & desenvolvimento , Lagos/microbiologia , Fitoplâncton/crescimento & desenvolvimento , Spirulina/crescimento & desenvolvimento , Biodiversidade , Biomassa , Clorofila A/metabolismo , Clorófitas/metabolismo , Ecossistema , Oceano Índico , Ilhas , Fitoplâncton/genética , Estações do Ano , Spirulina/metabolismo
8.
Microb Ecol ; 77(2): 288-303, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30019110

RESUMO

Two annual Baltic Sea phytoplankton blooms occur in spring and summer. The bloom intensity is determined by nutrient concentrations in the water, while the period depends on weather conditions. During the course of the bloom, dead cells sink to the sediment where their degradation consumes oxygen to create hypoxic zones (< 2 mg/L dissolved oxygen). These zones prevent the establishment of benthic communities and may result in fish mortality. The aim of the study was to determine how the spring and autumn sediment chemistry and microbial community composition changed due to degradation of diatom or cyanobacterial biomass, respectively. Results from incubation of sediment cores showed some typical anaerobic microbial processes after biomass addition such as a decrease in NO2- + NO3- in the sediment surface (0-1 cm) and iron in the underlying layer (1-2 cm). In addition, an increase in NO2- + NO3- was observed in the overlying benthic water in all amended and control incubations. The combination of NO2- + NO3- diffusion plus nitrification could not account for this increase. Based on 16S rRNA gene sequences, the addition of cyanobacterial biomass during autumn caused a large increase in ferrous iron-oxidizing archaea while diatom biomass amendment during spring caused minor changes in the microbial community. Considering that OTUs sharing lineages with acidophilic microorganisms had a high relative abundance during autumn, it was suggested that specific niches developed in sediment microenvironments. These findings highlight the importance of nitrogen cycling and early microbial community changes in the sediment due to sinking phytoplankton before potential hypoxia occurs.


Assuntos
Bactérias/isolamento & purificação , Cianobactérias/crescimento & desenvolvimento , Diatomáceas/crescimento & desenvolvimento , Sedimentos Geológicos/microbiologia , Fitoplâncton/crescimento & desenvolvimento , Bactérias/classificação , Bactérias/genética , Biomassa , Cianobactérias/classificação , Cianobactérias/genética , Cianobactérias/isolamento & purificação , Diatomáceas/classificação , Diatomáceas/genética , Diatomáceas/isolamento & purificação , Eutrofização , Sedimentos Geológicos/química , Nitratos/análise , Nitratos/metabolismo , Nitritos/análise , Nitritos/metabolismo , Filogenia , Fitoplâncton/classificação , Fitoplâncton/genética , Fitoplâncton/isolamento & purificação , Estações do Ano , Água do Mar/química , Água do Mar/microbiologia
9.
Mol Biol Evol ; 36(1): 4-14, 2019 01 01.
Artigo em Inglês | MEDLINE | ID: mdl-30351418

RESUMO

Larger populations are expected to have larger genetic diversity. However, as pointed out by Lewontin in 1974, the range of population sizes exceeds the range of genetic diversity by many orders of magnitude (a.k.a. "Lewontin's paradox," LP). The reasons for LP remain obscure. Here, This paper reports an extreme case of LP in astronomically large populations of the ubiquitous unicellular marine phytoplankton species Emiliania huxleyi (Haptophyta)-the species that accounts for 10-20% of primary productivity in the oceans and its blooms are so extensive that they are visible from space. This study demonstrates that despite the wide distribution and enormous population size, the world-wide sample of E. huxleyi strains with sequenced genomes represents a single cohesive species and contains surprisingly limited genetic diversity (π ∼ 0.006 per silent site). The patterns of polymorphism reveal even larger populations in the past, and frequent recombination (ρ ∼ 0.006) throughout the genome, ruling out demographic history and asexual reproduction as possible causes of low polymorphism in E. huxleyi. Natural selection wiping out genetic diversity at linked sites (a.k.a. "genetic draft") must be strong and frequent to account for low polymorphism in E. huxleyi. This study sheds the first light on poorly understood evolutionary genetic processes in astronomically large populations of marine microplankton.


Assuntos
Variação Genética , Haptófitas/genética , Fitoplâncton/genética , Taxa de Mutação , Densidade Demográfica , Seleção Genética
10.
Mol Ecol ; 28(5): 998-1008, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30592346

RESUMO

Diapause is a feature of the life cycle of many invertebrates by which unfavourable environmental conditions can be outlived. The seasonal timing of diapause allows organisms to adapt to seasonal changes in habitat suitability and thus is key to their fitness. In the planktonic crustacean Daphnia, various cues can induce the production of diapause stages that are resistant to heat, drought or freezing and contain one to two embryos in developmental arrest. Daphnia is a keystone species of many freshwater ecosystems, where it acts as the main link between phytoplankton and higher trophic levels. The correct seasonal timing of diapause termination is essential to maintain trophic interactions and is achieved via a genetically based interpretation of environmental cues like photoperiod and temperature. Field monitoring and modelling studies raised concerns on whether populations can advance their seasonal release from diapause to advances in spring phenology under global change, or if a failure to adapt will cause trophic mismatches negatively affecting ecosystem functioning. Our capacity to understand and predict the evolution of diapause timing requires information about the genetic architecture underlying this trait. In this study, we identified eight quantitative trait loci (QTLs) and four epistatic interactions that together explained 66.5% of the variation in diapause termination in Daphnia magna using QTL mapping. Our results suggest that the most significant QTL is modulating diapause termination dependent on photoperiod and is involved in three of the four detected epistatic interactions. Candidate genes at this QTL could be identified through the integration with genome data and included the presynaptic active zone protein bruchpilot. Our findings contribute to understanding the genomic control of seasonal diapause timing in an ecological relevant species.


Assuntos
Crustáceos/genética , Ecossistema , Plâncton/genética , Animais , Daphnia/genética , Daphnia/fisiologia , Diapausa/genética , Diapausa/fisiologia , Água Doce , Fotoperíodo , Fitoplâncton/genética , Locos de Características Quantitativas/genética , Estações do Ano
11.
PLoS One ; 13(12): e0209857, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30586428

RESUMO

Sydney Harbour is subjected to persistent stress associated with anthropogenic activity and global climate change, but is particularly subjected to pulse stress events associated with stormwater input during episodic periods of high rainfall. Photosynthetic microbes underpin metazoan diversity within estuarine systems and are therefore important bioindicators of ecosystem health; yet how stormwater input affects their occurrence and distribution in Sydney Harbour remains poorly understood. We utilised molecular tools (16S/18S rRNA and petB genes) to examine how the phytoplankton community structure (both prokaryotes and eukaryotes) within Sydney Harbour varies between high and low rainfall periods. The relative proportion of phytoplankton sequences was more abundant during the high rainfall period, comprising mainly of diatoms, an important functional group supporting increased productivity within estuarine systems, together with cyanobacteria. Increased spatial variability in the phytoplankton community composition was observed, potentially driven by the steepened physico-chemical gradients associated with stormwater inflow. Conversely, during a low rainfall period, the proportion of planktonic photosynthetic microbes was significantly lower and the persistent phytoplankton were predominantly represented by chlorophyte and dinoflagellate sequences, with lower overall diversity. Differences in phytoplankton composition between the high and low rainfall periods were correlated with temperature, salinity, total nitrogen and silicate. These results suggest that increased frequency of high-rainfall events may change the composition, productivity and health of the estuary. Our study begins to populate the knowledge gap in the phytoplankton community structure and substantial changes associated with transient environmental perturbations, an essential step towards unravelling the dynamics of primary production in a highly urbanised estuarine ecosystem in response to climate change and other anthropogenic stressors.


Assuntos
Estuários , Fitoplâncton/genética , Austrália , Cianobactérias , Diatomáceas , Monitoramento Ambiental/métodos , Fitoplâncton/classificação , Rios/microbiologia
12.
Protist ; 169(6): 958-975, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30453274

RESUMO

Ocean acidification (OA) and high light was found to negatively affect the Antarctic key species Phaeocystis antarctica, Fragilariopsis kerguelensis and Chaetoceros debilis. To unravel the underlying physiological response at the transcriptomic level, these species were grown under ambient and elevated pCO2 combined with low or high light. RNA sequencing revealed that the haptophyte was much more tolerant towards OA than the two diatoms as only these showed distinct OA-dependent gene regulation patterns. Under ambient pCO2, high light resulted in decreased glycolysis in P. antarctica. Contrastingly, upregulation of genes related to cell division and transcription as well as reduced expression of both cata- and anabolic carbon related pathways were seen in C. debilis. OA in combination with low light led to reduced respiration, but also surprisingly to higher expression of genes involved in light protection, transcription and translation in C. debilis. Though not affecting P. antarctica, OA combined with high light caused also photosensitivity in both diatoms. As additional response reallocation of carbon to lipids was found in C. debilis under these conditions. Overall, we conclude that P. antarctica is better adapted than the two diatoms to OA and high light.


Assuntos
Ácidos/toxicidade , Adaptação Fisiológica , Luz , Fitoplâncton/efeitos dos fármacos , Fitoplâncton/efeitos da radiação , Estresse Fisiológico , Dióxido de Carbono/metabolismo , Diatomáceas/efeitos dos fármacos , Diatomáceas/genética , Diatomáceas/fisiologia , Diatomáceas/efeitos da radiação , Perfilação da Expressão Gênica , Haptófitas/efeitos dos fármacos , Haptófitas/genética , Haptófitas/fisiologia , Haptófitas/efeitos da radiação , Redes e Vias Metabólicas/genética , Oceanos e Mares , Fitoplâncton/genética , Fitoplâncton/fisiologia , Água do Mar/química , Análise de Sequência de RNA
13.
Biotechniques ; 65(4): 219-223, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30284935

RESUMO

Ribosomal RNA analysis is a useful tool for characterization of microbial communities. However, the lack of broad-range primers has hampered the simultaneous analysis of eukaryotic and prokaryotic members by amplicon sequencing. We present a complete workflow for directional, primer-independent sequencing of size-selected small subunit ribosomal RNA fragments. The library preparation protocol includes gel extraction of the target RNA, ligation of an RNA oligo to the 5'-end of the target, and cDNA synthesis with a tailed random-hexamer primer and further barcoding. The sequencing results of a phytoplankton mock community showed a highly similar profile to the biomass indicators. This method has universal potential for microbiome studies, and is compatible for the 5'-end sequencing of other RNA types with minimum library preparation costs.


Assuntos
Biblioteca Gênica , Sequenciamento de Nucleotídeos em Larga Escala/métodos , RNA Ribossômico/genética , Primers do DNA/genética , DNA Complementar/genética , Fitoplâncton/genética , Fluxo de Trabalho
14.
Environ Microbiol ; 20(11): 4157-4169, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30246477

RESUMO

Dimethylsulfide (DMS), a dominant organic sulfur species in the surface ocean, may act as a signalling molecule and contribute to mutualistic interactions between bacteria and marine algae. These proposed functions depend on the DMS concentration in the vicinity of microorganisms. Here, we modelled the DMS enrichment at the surface of DMS-releasing marine algal cells as a function of DMS production rate, algal cell radius and turbulence. Our results show that the DMS concentration at the surface of unstressed phytoplankton with low DMS production rates can be enriched by <1 nM, whereas for mechanically stressed algae with high activities of the enzyme DMSP-lyase (a coccolithophore and a dinoflagellate) DMS cell surface enrichments can reach ~10 nM, and could potentially reach µM levels in large cells. These DMS enrichments are much higher than the median DMS concentration in the surface ocean (1.9 nM), and thus may attract and support the growth of bacteria living in the phycosphere. The bacteria in turn may provide photoactive iron chelators (siderophores) that enhance algal iron uptake and provide algal growth factors such as auxins and vitamins. The present study highlights new insights on the extent and impact of microscale DMS enrichments at algal surfaces, thereby contributing to our understanding of the potential chemoattractant and mutualistic roles of DMS in marine microorganisms.


Assuntos
Haptófitas/metabolismo , Fitoplâncton/metabolismo , Sulfetos/metabolismo , Bactérias/genética , Bactérias/crescimento & desenvolvimento , Bactérias/metabolismo , Liases de Carbono-Enxofre/genética , Liases de Carbono-Enxofre/metabolismo , Diatomáceas/enzimologia , Diatomáceas/genética , Diatomáceas/metabolismo , Dinoflagelados/enzimologia , Dinoflagelados/genética , Dinoflagelados/metabolismo , Ecossistema , Haptófitas/enzimologia , Haptófitas/genética , Ferro/metabolismo , Fitoplâncton/enzimologia , Fitoplâncton/genética , Água do Mar/microbiologia , Água do Mar/parasitologia , Sideróforos/metabolismo , Sulfetos/análise
15.
Protist ; 169(5): 615-631, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30096708

RESUMO

To understand the diversity of the diatom genus Chaetoceros Ehrenberg, the C. lorenzianus complex was previously chosen as a model and three new species were described. In the present study, yet another new species, Chaetoceros pauciramosus sp. nov., was discovered from Chinese tropical waters and the temperate south-eastern Baltic Sea. In the latter locality it has been known since 2003 and identified as C. cf lorenzianus, and now found to comprise a dominating component of the autumn phytoplankton community. Vegetative cells and resting spores were examined by light and electron microscopy. The LSU and SSU of the nuclear rDNA were sequenced. The characters suggesting that C. pauciramosus belongs to C. lorenzianus complex are: 1) the vegetative cells contain four or more chloroplasts, 2) the cells have stiff setae and form regular straight chains, 3) the terminal setae differ in the direction from the intercalary setae. The relationship was well-supported by molecular phylogenetic analyses inferred from both LSU and SSU markers. The primary valve of the resting spore has two conical elevations, each with dichotomously branching processes, similar to other species in the C. lorenzianus complex. Each process forms a tree-like structure with the pointed distal tips which possess one or two thin spikes, that distinguishes C. pauciramosus from allied taxa. In the phylogenetic trees, Chaetoceros pauciramosus clustered with C. elegans, in agreement with their morphologically similar resting spores.


Assuntos
Diatomáceas/isolamento & purificação , Fitoplâncton/isolamento & purificação , Águas Salinas/análise , Água do Mar/parasitologia , China , DNA Ribossômico/genética , Diatomáceas/classificação , Diatomáceas/genética , Diatomáceas/crescimento & desenvolvimento , Filogenia , Fitoplâncton/classificação , Fitoplâncton/genética , Fitoplâncton/crescimento & desenvolvimento , Água do Mar/análise
16.
Environ Microbiol ; 20(8): 3069-3082, 2018 08.
Artigo em Inglês | MEDLINE | ID: mdl-30043484

RESUMO

Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment.


Assuntos
Diatomáceas/classificação , Diatomáceas/genética , Fitoplâncton/classificação , Fitoplâncton/genética , Evolução Biológica , California , Diatomáceas/metabolismo , Ecossistema , Expressão Gênica , Fitoplâncton/metabolismo
17.
ISME J ; 12(11): 2807-2810, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30013161

RESUMO

Metabarcoding has offered unprecedented insights into microbial diversity. In many studies, short DNA sequences are binned into consecutively lower Linnaean ranks, and ranked groups (e.g., genera) are the units of biodiversity analyses. These analyses assume that Linnaean ranks are biologically meaningful and that identically ranked groups are comparable. We used a metabarcode dataset for marine planktonic diatoms to illustrate the limits of this approach. We found that the 20 most abundant marine planktonic diatom genera ranged in age from 4 to 134 million years, indicating the non-equivalence of genera because some have had more time to diversify than others. However, species richness was largely independent of genus age, suggesting that disparities in species richness among genera were better explained by variation in rates of speciation and extinction. Taxonomic classifications often do not reflect phylogeny, so genus-level analyses can include phylogenetically nested genera, further confounding rank-based analyses. These results underscore the indispensable role of phylogeny in understanding patterns of microbial diversity.


Assuntos
Diatomáceas/classificação , Biodiversidade , Código de Barras de DNA Taxonômico , Diatomáceas/genética , Diatomáceas/isolamento & purificação , Filogenia , Fitoplâncton/classificação , Fitoplâncton/genética , Fitoplâncton/isolamento & purificação
18.
Toxicon ; 151: 5-14, 2018 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-29935922

RESUMO

In fjord systems, Harmful Algal Blooms (HABs) not only constitute a serious problem when affecting the wildlife and ecosystems, but also human health and economic activities related to the marine environment. This is mostly due to a broad spectrum of toxic compounds produced by several members of the phytoplankton. Nevertheless, a deep coverage of the taxonomic diversity and composition of phytoplankton species and phycotoxin profiles in HAB prone areas are still lacking and little is known about the relationship between these fundamental elements for fjord ecosystems. In this study, a detailed molecular and microscopic characterization of plankton communities was performed, together with an analysis of the occurrence and spatial patterns of lipophilic toxins in a HAB prone area, located in the Southeastern Pacific fjord region. Microscopy and molecular analyses based on the 18S rRNA gene fragment indicated high diversity and taxonomic homogeneity among stations. Four toxigenic genera were identified: Pseudo-nitzschia, Dinophysis, Prorocentrum, and Alexandrium. In agreement with the detected species, liquid chromatography coupled with mass spectrometry revealed the presence of domoic acid (DA), pectenotoxin-2 (PTX-2), dinophysistoxin-2 (DTX-2), and 13-desmethyl spirolide C (SPX-1). Furthermore, a patchy distribution among DA in different net haul size fractions was found. Our results displayed a complex phytoplankton-phycotoxin pattern and for the first time contribute to the characterization of high-resolution phytoplankton community composition and phycotoxin distribution in fjords of the Southeastern Pacific region.


Assuntos
Biodiversidade , Estuários , Toxinas Marinhas/química , Toxinas Marinhas/metabolismo , Fitoplâncton/genética , Fitoplâncton/metabolismo , Chile , Sequenciamento de Nucleotídeos em Larga Escala
19.
J Phycol ; 54(4): 557-570, 2018 08.
Artigo em Inglês | MEDLINE | ID: mdl-29908074

RESUMO

Some diatoms are able to colonize as epibionts on their potential zooplankton predators. Here, we report Pseudohimantidium pacificum living on the copepod Corycaeus giesbrechti and as a new finding on Oithona nana, Protoraphis atlantica living on the copepod Pontellopsis brevis, Protoraphis hustedtiana on the cypris larvae of barnacles, and Falcula hyalina on the copepod Acartia lilljeborgii. The epizoic diatoms were able to grow as free-living forms under culture conditions. Pseudohimantidium pacificum and P. atlantica appeared as the most derived species from their benthic diatom ancestors. The mucilage pad or stalk of the strains of these species showed important morphological distinction when compared with their epizoic forms. Barnacle larvae explore benthic habitats before settlement, and epibiosis on them is an example where P. hustedtiana profits from the host behavior for dispersal of its benthic populations. Molecular phylogenies based on the SSU rRNA and RuBisCO large subunit (rbcL) gene sequences revealed F. hyalina as an independent lineage within the Fragilariales (Tabularia, Catacombas, and others), consistent with its morphological distinction in the low number of rows (≤6) in the ocellulimbus, among other features. We propose the transfer of F. hyalina to the genus Pseudofalcula gen. nov. Molecular phylogeny suggests a single order for the members of the Cyclophorales and the Protoraphidales, and that the epibioses of araphid diatoms on marine zooplankton have been independently acquired several times. These clades are constituted of both epizoic and epiphytic/epilithic forms that evidence a recent acquisition of the epizoic modus vivendi.


Assuntos
Diatomáceas/classificação , Zooplâncton/classificação , Animais , DNA Ribossômico/análise , Diatomáceas/citologia , Diatomáceas/genética , Diatomáceas/ultraestrutura , Microscopia Eletrônica de Varredura , Filogenia , Fitoplâncton/classificação , Fitoplâncton/citologia , Fitoplâncton/genética , Fitoplâncton/ultraestrutura , Ribulose-Bifosfato Carboxilase/análise , Zooplâncton/citologia , Zooplâncton/genética , Zooplâncton/ultraestrutura
20.
ISME J ; 12(10): 2417-2432, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29899514

RESUMO

Short timescale observations are valuable for understanding microbial ecological processes. We assessed dynamics in relative abundance and potential activities by sequencing the small sub-unit ribosomal RNA gene (rRNA gene) and rRNA molecules (rRNA) of Bacteria, Archaea, and Eukaryota once to twice daily between March 2014 and May 2014 from the surface ocean off Catalina Island, California. Typically Ostreococcus, Braarudosphaera, Teleaulax, and Synechococcus dominated phytoplankton sequences (including chloroplasts) while SAR11, Sulfitobacter, and Fluviicola dominated non-phytoplankton Bacteria and Archaea. We observed short-lived increases of diatoms, mostly Pseudo-nitzschia and Chaetoceros, with quickly responding Bacteria and Archaea including Flavobacteriaceae (Polaribacter & Formosa), Roseovarius, and Euryarchaeota (MGII), notably the exact amplicon sequence variants we observed responding similarly to another diatom bloom nearby, 3 years prior. We observed correlations representing known interactions among abundant phytoplankton rRNA sequences, demonstrating the biogeochemical and ecological relevance of such interactions: (1) The kleptochloroplastidic ciliate Mesodinium 18S rRNA gene sequences and a single Teleaulax taxon (via 16S rRNA gene sequences) were correlated (Spearman r = 0.83) yet uncorrelated to a Teleaulax 18S rRNA gene OTU, or any other taxon (consistent with a kleptochloroplastidic or karyokleptic relationship) and (2) the photosynthetic prymnesiophyte Braarudosphaera bigelowii and two strains of diazotrophic cyanobacterium UCYN-A were correlated and each taxon was also correlated to other taxa, including B. bigelowii to a verrucomicrobium and a dictyochophyte phytoplankter (all r > 0.8). We also report strong correlations (r > 0.7) between various ciliates, bacteria, and phytoplankton, suggesting interactions via currently unknown mechanisms. These data reiterate the utility of high-frequency time series to show rapid microbial reactions to stimuli, and provide new information about in situ dynamics of previously recognized and hypothesized interactions.


Assuntos
Archaea/genética , Bactérias/genética , Haptófitas/genética , Fitoplâncton/genética , Plâncton/classificação , Plâncton/fisiologia , Diatomáceas/genética , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico 18S/genética , Água do Mar/microbiologia
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