A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations（〈 10–500 μg/L P） and environmentally realistic concentrations of arsenate（As（Ⅴ））（5–50 μg/L As）. A...A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations（〈 10–500 μg/L P） and environmentally realistic concentrations of arsenate（As（Ⅴ））（5–50 μg/L As）. Arsenic speciation in the culture medium and total cellular arsenic were measured using AEC-ICP-MS and ICP-DRC-MS, respectively, to determine arsenic biotransformation and uptake in the various phosphorus scenarios. At high phosphate concentration in the culture medium, 〉 100 μg/L P, the uptake and biotransformation of As（Ⅴ） was minimal and dimethylarsonate（DMAs（Ⅴ）） was the dominant metabolite excreted by C. vulgaris, albeit at relatively low concentrations. At common environmental P concentrations, 0–50 μg/L P, the uptake and biotransformation of As（Ⅴ） increased. At these higher As-uptake levels, arsenite（As（Ⅲ）） was the predominant metabolite excreted from the cell. The concentrations of As（Ⅲ） in these low P conditions were much higher than the concentrations of methylated arsenicals observed at the various P concentrations studied. The switchover threshold between the（small） methylation and（large） reduction of As（Ⅴ） occurred around a cellular As concentration of 1 fg/cell. The observed nearly quantitative conversion of As（Ⅴ） to As（Ⅲ） under low phosphate conditions indicates the importance of As（Ⅴ） bio-reduction at common freshwater P concentrations. These findings on the influence of phosphorus on arsenic uptake, accumulation and excretion are discussed in relation to previously published research. The impact that the two scenarios of As（Ⅴ） metabolism, As（Ⅲ） excretion at high As（Ⅴ）-uptake and methylarsenical excretion at low As（Ⅴ）-uptake, have on freshwater arsenic speciation is discussed.展开更多
Three new species of Batrachospermum Roth (Batrachospermales, Rhodophyta) from China are described in this paper. B. yunnanense sp. nov. has long-cylindrical trichogynes with long stalks and is diagnostic of section V...Three new species of Batrachospermum Roth (Batrachospermales, Rhodophyta) from China are described in this paper. B. yunnanense sp. nov. has long-cylindrical trichogynes with long stalks and is diagnostic of section Virescentia. Within this section, B. yunnanense is similar to B. helminthosum Bory emend. Sheath et al., but it is dioecious and has curved carpogonial branches, while the latter is monoecious and has straight carpogonial branches. It is also similar to B. transtaganum Reis, but it differs from the latter in long carpogonia, big carposporophytes and carposporangia. It is considered that B. nothocladoideum sp. nov. is assigned to section Contorta, subsection Kushiroense, because its carpogonial branches are twisted and gonimoblast filaments are loosely agglomerated. This new species similar to B. iriomotense Kumano, but with short fascicles, long-ovoid or subpyriform cells, numerous terminal hairs, long-ellipsoid trichogynes, big carposporophytes and small carpo- sporangia. The plant is quite tough and cartilaginous and similar to Nothocladus in gross morphology, but its carposporophytes are compact instead of diffuse. This shows that it may be a transitional species between section Contorta and genus Nothocladus. So, B. transitorium sp. nov. should belong to section Contorta, subsection Kushiroense, because of its curved or twisted carpogonial branches and loosely agglomerated gonimoblast filaments, with globose or subglobose cells in fascicles similar to B. spermatiophorum Vis et Sheath, but no colourless spermatiophores. In terms of small and numerous carposporophytes, B. transitorium sp. nov. is similar to some species of section Batrachospermum. However, their other features are unique, indicating its transitional nature between section Contorta and Batrachospermum.展开更多
Freshwater brown algae have been acknowledged as the least diverse of all groups of freshwater algae. Morphological and molecular investigation were conducted on a freshwater brown alga collected in this study. Morpho...Freshwater brown algae have been acknowledged as the least diverse of all groups of freshwater algae. Morphological and molecular investigation were conducted on a freshwater brown alga collected in this study. Morphological characterization and phylogenetic tree based on the rbcL gene confirmed its attribution to Heribaudiella fluviatilis. The complete organelle genomes of H. fluviatilis were determined and assembled from high-throughput sequencing. A circular tetrad structure of 128,880 bp was identified for the chloroplast, and the mitochondrial genome was assembled as a circle with 43,657 bp in length. This study provides the first and only record of organelle genomic information of the freshwater Phaeophyceae, which are important for understanding the endosymbiosis theories. Concatenated (Bayesian inference, maximum likelihood under MFP and GHOST models) and coalescent methods were used to construct the phylogenetic relationship among secondary plastid-bearing lineages based on organelle genomes. Obvious conflicts were observed in grouping relationships of chloroplast and mitochondrial genomes, even among different evolutionary models and tree-constructing methods. The transcriptome of H. fluviatilis was sequenced and used to construct the phylogenetic relationship among secondary plastid-bearing lineages. The phylogenetic relationships in nuclear and mitochondrial genomes were consistent in grouping CHSR taxa (cryptophytes, haptophytes, stramenopiles and rhizarians) in an independent branch. The phylogenetic relationship constructed from nuclear transcriptomes was highly reliable by owning robust supporting values on each node and was consistent with the serial endosymbiosis theory on evolution of red secondary plastid-derived lineages.展开更多
基金provided by the Ontario Ministry of the Environment's ‘Best in Science’ program
文摘A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations（〈 10–500 μg/L P） and environmentally realistic concentrations of arsenate（As（Ⅴ））（5–50 μg/L As）. Arsenic speciation in the culture medium and total cellular arsenic were measured using AEC-ICP-MS and ICP-DRC-MS, respectively, to determine arsenic biotransformation and uptake in the various phosphorus scenarios. At high phosphate concentration in the culture medium, 〉 100 μg/L P, the uptake and biotransformation of As（Ⅴ） was minimal and dimethylarsonate（DMAs（Ⅴ）） was the dominant metabolite excreted by C. vulgaris, albeit at relatively low concentrations. At common environmental P concentrations, 0–50 μg/L P, the uptake and biotransformation of As（Ⅴ） increased. At these higher As-uptake levels, arsenite（As（Ⅲ）） was the predominant metabolite excreted from the cell. The concentrations of As（Ⅲ） in these low P conditions were much higher than the concentrations of methylated arsenicals observed at the various P concentrations studied. The switchover threshold between the（small） methylation and（large） reduction of As（Ⅴ） occurred around a cellular As concentration of 1 fg/cell. The observed nearly quantitative conversion of As（Ⅴ） to As（Ⅲ） under low phosphate conditions indicates the importance of As（Ⅴ） bio-reduction at common freshwater P concentrations. These findings on the influence of phosphorus on arsenic uptake, accumulation and excretion are discussed in relation to previously published research. The impact that the two scenarios of As（Ⅴ） metabolism, As（Ⅲ） excretion at high As（Ⅴ）-uptake and methylarsenical excretion at low As（Ⅴ）-uptake, have on freshwater arsenic speciation is discussed.
基金Project No. 30270119 and 39899400 supported by the National Nature Science Foundation of China.
文摘Three new species of Batrachospermum Roth (Batrachospermales, Rhodophyta) from China are described in this paper. B. yunnanense sp. nov. has long-cylindrical trichogynes with long stalks and is diagnostic of section Virescentia. Within this section, B. yunnanense is similar to B. helminthosum Bory emend. Sheath et al., but it is dioecious and has curved carpogonial branches, while the latter is monoecious and has straight carpogonial branches. It is also similar to B. transtaganum Reis, but it differs from the latter in long carpogonia, big carposporophytes and carposporangia. It is considered that B. nothocladoideum sp. nov. is assigned to section Contorta, subsection Kushiroense, because its carpogonial branches are twisted and gonimoblast filaments are loosely agglomerated. This new species similar to B. iriomotense Kumano, but with short fascicles, long-ovoid or subpyriform cells, numerous terminal hairs, long-ellipsoid trichogynes, big carposporophytes and small carpo- sporangia. The plant is quite tough and cartilaginous and similar to Nothocladus in gross morphology, but its carposporophytes are compact instead of diffuse. This shows that it may be a transitional species between section Contorta and genus Nothocladus. So, B. transitorium sp. nov. should belong to section Contorta, subsection Kushiroense, because of its curved or twisted carpogonial branches and loosely agglomerated gonimoblast filaments, with globose or subglobose cells in fascicles similar to B. spermatiophorum Vis et Sheath, but no colourless spermatiophores. In terms of small and numerous carposporophytes, B. transitorium sp. nov. is similar to some species of section Batrachospermum. However, their other features are unique, indicating its transitional nature between section Contorta and Batrachospermum.
基金funded by the National Natural Science Foundation of China(No.31800172 to F.R.Nan,No.32170204 to S.L.Xie,No.32270220 and U22A20445 to J.Feng)the Excellent Achievement Cultivation Project of Higher education in Shanxi(No.2020KJ029).
文摘Freshwater brown algae have been acknowledged as the least diverse of all groups of freshwater algae. Morphological and molecular investigation were conducted on a freshwater brown alga collected in this study. Morphological characterization and phylogenetic tree based on the rbcL gene confirmed its attribution to Heribaudiella fluviatilis. The complete organelle genomes of H. fluviatilis were determined and assembled from high-throughput sequencing. A circular tetrad structure of 128,880 bp was identified for the chloroplast, and the mitochondrial genome was assembled as a circle with 43,657 bp in length. This study provides the first and only record of organelle genomic information of the freshwater Phaeophyceae, which are important for understanding the endosymbiosis theories. Concatenated (Bayesian inference, maximum likelihood under MFP and GHOST models) and coalescent methods were used to construct the phylogenetic relationship among secondary plastid-bearing lineages based on organelle genomes. Obvious conflicts were observed in grouping relationships of chloroplast and mitochondrial genomes, even among different evolutionary models and tree-constructing methods. The transcriptome of H. fluviatilis was sequenced and used to construct the phylogenetic relationship among secondary plastid-bearing lineages. The phylogenetic relationships in nuclear and mitochondrial genomes were consistent in grouping CHSR taxa (cryptophytes, haptophytes, stramenopiles and rhizarians) in an independent branch. The phylogenetic relationship constructed from nuclear transcriptomes was highly reliable by owning robust supporting values on each node and was consistent with the serial endosymbiosis theory on evolution of red secondary plastid-derived lineages.
