A new marine prasinophyte genus alternates between a flagellate and a dominant benthic stage with microrhizoids for adhesion

Bringloe

Costa

et al. 2020

Journal of Phycology

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Pelagophytes (Heterokonta) are a morphologically diverse class of marine algae historically united only by DNA sequences. We established clonal cultures of sand‐dwelling pelagophytes collected from intertidal pools around Australia. Phylogenetic trees based on nuclear 18S rDNA and plastid rbcL, psaA, psaB, psbA, and psbC sequences revealed two new genera, Gazia and Glomerochrysis, related to Aureoumbra in a distinct lineage within the Sarcinochrysidaceae (Pelagophyceae). The three new species (Gazia saundersii, Gazia australica, and Glomerochrysis psammophila), along with an Australian strain of Aureoumbra geitleri, are characterized by dominant benthic stages that differ significantly from one another, while occasionally producing classic heterokont zoospores. The benthic stage of Ga. saundersii has a novel development not observed in any other colonial alga, consisting of large, spherical colonies (up to 140 μm in diameter) containing c. 2,500 cells that eventually differentiate and segregate into a large number of daughter colonies that are subsequently liberated. Alternatively, colonies may differentiate into a mass of zoospores that escape and settle to develop into new colonies. In Gl. psammophila, cubic packets of cells form large sticky clusters that bind sand together, while Ga. australica and A. geitleri are unicellular species. Using fixation by high‐pressure freezing, a distinctive perforated theca was observed by TEM in all genera of this lineage, and we hypothesize this unique covering may be the first morphological feature to characterize most, if not all, pelagophytes. This study substantiates the diverse nature of sand‐dwelling pelagophytes as well as their mechanisms for thriving in a dynamic habitat.

mentioning

confidence: 77%

New pelagophytes show a novel mode of algal colony development and reveal a perforated theca that may define the class

Bringloe

Costa

et al. 2020

Journal of Phycology

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“…Algal strains were isolated from marine sand ( Microrhizoidea pickettheapsiorum [ 36 ]; Kraftionema allantoideum [ 37 ]; Chlorarachnion reptans and Lotharella sp. from the Wye River, Victoria, Australia) or coral skeletons ( Ostreobium sp.…”

Section: Methodsmentioning

confidence: 99%

Metatranscriptomic Identification of Diverse and Divergent RNA Viruses in Green and Chlorarachniophyte Algae Cultures

Charon

Marcelino

et al. 2020

Viruses

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Our knowledge of the diversity and evolution of the virosphere will likely increase dramatically with the study of microbial eukaryotes, including the microalgae within which few RNA viruses have been documented. By combining total RNA sequencing with sequence and structural-based homology detection, we identified 18 novel RNA viruses in cultured samples from two major groups of microbial algae: the chlorophytes and the chlorarachniophytes. Most of the RNA viruses identified in the green algae class Ulvophyceae were related to the Tombusviridae and Amalgaviridae viral families commonly associated with land plants. This suggests that the evolutionary history of these viruses extends to divergence events between algae and land plants. Seven Ostreobium sp-associated viruses exhibited sequence similarity to the mitoviruses most commonly found in fungi, compatible with horizontal virus transfer between algae and fungi. We also document, for the first time, RNA viruses associated with chlorarachniophytes, including the first negative-sense (bunya-like) RNA virus in microalgae, as well as a distant homolog of the plant virus Virgaviridae, potentially signifying viral inheritance from the secondary chloroplast endosymbiosis that marked the origin of the chlorarachniophytes. More broadly, these data suggest that the scarcity of RNA viruses in algae results from limited investigation rather than their absence.

“…Algal strains were isolated from marine sand (Microrhizoidea pickettheapsiorum 59 ; (Table S1), due to the low amount of input RNAs in these libraries. The resulting libraries were sequenced on an Illumina HiSeq2500 (paired-end, 100bp) at the AGRF.…”

Section: Algal Culturesmentioning

confidence: 99%

Meta-transcriptomic detection of diverse and divergent RNA viruses in green and chlorarachniophyte algae

Charon

et al. 2020

Preprint

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24Our knowledge of the diversity and evolution of the virosphere will likely increase 25 dramatically with the study of microbial eukaryotes, including the microalgae in few RNA 26 viruses have been documented to date. By combining meta-transcriptomic approaches 27 with sequence and structural-based homology detection, followed by PCR confirmation, we 28 identified 18 novel RNA viruses in two major groups of microbial algae -the chlorophytes 29 and the chlorarachniophytes. Most of the RNA viruses identified in the green algae class 30 Ulvophyceae were related to those from the families Tombusviridae and Amalgaviridae that 31 have previously been associated with plants, suggesting that these viruses have an 32 evolutionary history that extends to when their host groups shared a common ancestor. In 33 contrast, seven ulvophyte associated viruses exhibited clear similarity with the mitoviruses 34 that are most commonly found in fungi. This is compatible with horizontal virus transfer 35 between algae and fungi, although mitoviruses have recently been documented in plants. 36 We also document, for the first time, RNA viruses in the chlorarachniophytes, including the 37 first observation of a negative-sense (bunya-like) RNA virus in microalgae. The other virus-38 like sequence detected in chlorarachniophytes is distantly related to those from the plant 39 virus family Virgaviridae, suggesting that they may have been inherited from the secondary 40 chloroplast endosymbiosis event that marked the origin of the chlorarachniophytes. More 41 broadly, this work suggests that the scarcity of RNA viruses in algae most likely results from 42 limited investigation rather than their absence. Greater effort is needed to characterize the 43 RNA viromes of unicellular eukaryotes, including through structure-based methods that are 44 able to detect distant homologies, and with the inclusion of a wider range of eukaryotic 45 microorganisms. 46 47 Author summary 48 3 RNA viruses are expected to infect all living organisms on Earth. Despite recent 49 developments in and the deployment of large-scale sequencing technologies, our 50 understanding of the RNA virosphere remains anthropocentric and largely restricted to 51 human, livestock, cultivated plants and vectors for viral disease. However, a broader 52 investigation of the diversity of RNA viruses, especially in protists, is expected to answer 53 fundamental questions about their origin and long-term evolution. This study first 54 investigates the RNA virus diversity in unicellular algae taxa from the phylogenetically 55 distinct ulvophytes and chlorarachniophytes taxa. Despite very high levels of sequence 56 divergence, we were able to identify 18 new RNA viruses, largely related to plant and fungi 57 viruses, and likely illustrating a past history of horizontal transfer events that have occurred 58 during RNA virus evolution. We also hypothesise that the sequence similarity between a 59 chlorarachniophyte-associated virga-like virus and members of Virgaviridae...