RESUMO
To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.
Assuntos
Diatomáceas , Diatomáceas/química , Plâncton , Oceanos e Mares , DNA Ribossômico , ChileRESUMO
The vertical distribution of phytoplankton is of fundamental importance in the structure, dynamic, and biogeochemical pathways in marine ecosystems. Nevertheless, what are the main factors determining this distribution remains as an open question. Here, we evaluated the relative influence of environmental factors that might control the coexistence and vertical distribution of pico-nanoplankton associated with the OMZ off northern Chile. Our results showed that in the upper layer Synechococcus-like cells were numerically important at all sampling stations. Pico-nano eukaryotes and phototrophic nanoflagellates (PNF) also showed high abundances in the upper layer decreasing in abundance down to the upper oxycline, while only Prochlorococcus showed high abundances under oxycline and within the oxygen-depleted layer. Statistical analyses evidenced that temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton. Additionally, we experimentally-evaluated the combined effect of low pH/low O2 conditions on a nanophytoplankton species, the haptophyte Imantonia sp. Under control conditions (pH = 8.1; O2 = 287.5 µM, light = 169.6 µEm-2s-1), Imantonia sp. in vivo fluorescence increased over fifty times, inducing supersaturated O2 conditions (900 µM) and an increasing pH (8.5), whereas upon an experimental treatment mimicking OMZ conditions (pH = 7.5; O2 = 55.6 µM; light = 169.6 µEm-2s-1), in vivo fluorescence declined dramatically, suggesting that Imantonia sp. did not survive. Although preliminary, our study provides evidence about the role of low pH/low O2 conditions on the vertical distribution of nanophytoplankton, which deserve future attention through both fieldwork and more extended experimental experiences.
Assuntos
Oxigênio , Água do Mar , Chile , Ecossistema , Concentração de Íons de Hidrogênio , Oxigênio/metabolismo , Água do Mar/químicaRESUMO
Anoxic marine zones (AMZs) impact biogeochemical cycles at the global scale, particularly the nitrogen cycle. Key microbial players from AMZs have been identified, but the majority remains unrecognized or uncharacterized. Thirty-one single-cell amplified genomes (SAGs) from the eastern tropical North and South Pacific AMZs were sequenced to gain insight into the distribution, metabolic potential and contribution to the community transcriptional profile of these uncharacterized bacterial and archaeal groups. Detailed analyses focused on SAG-bins assigned to three of these groups that presented 79%-100% estimated genome completeness: the putative sulphur-oxidizing Gamaproteobacteria EOSA II clade, a Marinimicrobia member of the recently recognized PN262000N21 clade found to be abundant in AMZ anoxic cores, and a representative of the Marine Benthic Group A Thaumarchaeota. Community-based analyses revealed that these three groups are significantly more abundant and transcriptionally more active in the AMZ microbial communities than previously described phylogenetically related microbial groups. Collectively, these groups have the potential to link biogeochemically relevant processes by coupling the carbon, nitrogen and sulfur cycles. Together, these results increase our understanding of key microbial components inhabiting AMZs and other oxygen-deficient marine environments, enhancing our capacity to predict the impact of the expansion of these ecosystems due to climate change.
Assuntos
Archaea/metabolismo , Bactérias/metabolismo , Carbono/metabolismo , Nitrogênio/metabolismo , Enxofre/metabolismo , Archaea/classificação , Archaea/genética , Bactérias/classificação , Bactérias/genética , Gammaproteobacteria/genética , Gammaproteobacteria/metabolismo , Microbiota , Filogenia , Água do Mar/microbiologia , TranscriptomaRESUMO
The coccolithophore genus Gephyrocapsa contains a cosmopolitan assemblage of pelagic species, including the bloom-forming Gephyrocapsa oceanica, and is closely related to the emblematic coccolithophore Emiliania huxleyi within the Noëlaerhabdaceae. These two species have been extensively studied and are well represented in culture collections, whereas cultures of other species of this family are lacking. We report on three new strains of Gephyrocapsa isolated into culture from samples from the Chilean coastal upwelling zone using a novel flow cytometric single-cell sorting technique. The strains were characterized by morphological analysis using scanning electron microscopy and phylogenetic analysis of 6 genes (nuclear 18S and 28S rDNA, plastidial 16S and tufA, and mitochondrial cox1 and cox3 genes). Morphometric features of the coccoliths indicate that these isolates are distinct from G. oceanica and best correspond to G. muellerae. Surprisingly, both plastidial and mitochondrial gene phylogenies placed these strains within the E. huxleyi clade and well separated from G. oceanica isolates, making Emiliania appear polyphyletic. The only nuclear sequence difference, 1bp in the 28S rDNA region, also grouped E. huxleyi with the new Gephyrocapsa isolates and apart from G. oceanica. Specifically, the G. muellerae morphotype strains clustered with the mitochondrial ß clade of E. huxleyi, which, like G. muellerae, has been associated with cold (temperate and sub-polar) waters. Among putative evolutionary scenarios that could explain these results we discuss the possibility that E. huxleyi is not a valid taxonomic unit, or, alternatively the possibility of past hybridization and introgression between each E. huxleyi clade and older Gephyrocapsa clades. In either case, the results support the transfer of Emiliania to Gephyrocapsa. These results have important implications for relating morphological species concepts to ecological and evolutionary units of diversity.
Assuntos
Haptófitas/classificação , Haptófitas/ultraestrutura , Filogenia , Biodiversidade , Chile , Genes de Protozoários/genética , Haptófitas/genética , Haptófitas/isolamento & purificação , Oceano Pacífico , Especificidade da EspécieRESUMO
Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells. We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells. Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales. This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability. Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton. Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers.
Assuntos
Haptófitas/genética , Oceanos e Mares , Fitoplâncton/genética , Animais , Biomassa , Clorofila/química , Biologia Computacional , Diploide , Ecologia , Flagelos/metabolismo , Perfilação da Expressão Gênica , Marcadores Genéticos/genética , Genoma , Genômica , Genótipo , Estágios do Ciclo de VidaRESUMO
Cáhuil Lagoon in central Chile harbors distinct microbial communities in various solar salterns that are arranged as interconnected ponds with increasing salt concentrations. Here, we report the metagenome of the 3.0- to 0.2-µm fraction of the microbial community present in a crystallizer pond with 34% salinity.