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Phylogenetic and ecological analysis of novel marine stramenopiles.

ABSTRACT: Culture-independent molecular analyses of open-sea microorganisms have revealed the existence and apparent abundance of novel eukaryotic lineages, opening new avenues for phylogenetic, evolutionary, and ecological research. Novel marine stramenopiles, identified by 18S ribosomal DNA sequences within the basal part of the stramenopile radiation but unrelated to any previously known group, constituted one of the most important novel lineages in these open-sea samples. Here we carry out a comparative analysis of novel stramenopiles, including new sequences from coastal genetic libraries presented here and sequences from recent reports from the open ocean and marine anoxic sites. Novel stramenopiles were found in all major habitats, generally accounting for a significant proportion of clones in genetic libraries. Phylogenetic analyses indicated the existence of 12 independent clusters. Some of these were restricted to anoxic or deep-sea environments, but the majority were typical components of coastal and open-sea waters. We specifically identified four clusters that were well represented in most marine surface waters (together they accounted for 74% of the novel stramenopile clones) and are the obvious targets for future research. Many sequences were retrieved from geographically distant regions, indicating that some organisms were cosmopolitan. Our study expands our knowledge on the phylogenetic diversity and distribution of novel marine stramenopiles and confirms that they are fundamental members of the marine eukaryotic picoplankton.

SUBMITTER: Massana R

PROVIDER: S-EPMC427732 | biostudies-literature | 2004 Jun

REPOSITORIES: biostudies-literature

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Phylogenetic and ecological analysis of novel marine stramenopiles.

Massana Ramon R Castresana Jose J Balagué Vanessa V Guillou Laure L Romari Khadidja K Groisillier Agnès A Valentin Klaus K Pedrós-Alió Carlos C

Applied and environmental microbiology 20040601 6

Culture-independent molecular analyses of open-sea microorganisms have revealed the existence and apparent abundance of novel eukaryotic lineages, opening new avenues for phylogenetic, evolutionary, and ecological research. Novel marine stramenopiles, identified by 18S ribosomal DNA sequences within the basal part of the stramenopile radiation but unrelated to any previously known group, constituted one of the most important novel lineages in these open-sea samples. Here we carry out a comparati ...[more]

PMID: 15184153

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Project description:The Heterokonta or Stramenopile phylum comprises clades of unicellular photosynthetic species, which are promising for a broad range of biotechnological applications, based on their capacity to capture atmospheric CO2 via photosynthesis and produce biomolecules of interest. These molecules include triacylglycerol (TAG) loaded inside specific cytosolic bodies, called the lipid droplets (LDs). Understanding TAG production and LD biogenesis and function in photosynthetic stramenopiles is therefore essential, and is mostly based on the study of a few emerging models, such as the pennate diatom Phaeodactylum tricornutum and eustigmatophytes, such as Nannochloropsis and Microchloropsis species. The biogenesis of cytosolic LD usually occurs at the level of the endoplasmic reticulum. However, stramenopile cells contain a complex plastid deriving from a secondary endosymbiosis, limited by four membranes, the outermost one being connected to the endomembrane system. Recent cell imaging and proteomic studies suggest that at least some cytosolic LDs might be associated to the surface of the complex plastid, via still uncharacterized contact sites. The carbon length and number of double bonds of the acyl groups contained in the TAG molecules depend on their origin. De novo synthesis produces long-chain saturated or monounsaturated fatty acids (SFA, MUFA), whereas subsequent maturation processes lead to very long-chain polyunsaturated FA (VLC-PUFA). TAG composition in SFA, MUFA, and VLC-PUFA reflects therefore the metabolic context that gave rise to the formation of the LD, either via an early partitioning of carbon following FA de novo synthesis and/or a recycling of FA from membrane lipids, e.g., plastid galactolipids or endomembrane phosphor- or betaine lipids. In this review, we address the relationship between cytosolic LDs and the complex membrane compartmentalization within stramenopile cells, the metabolic routes leading to TAG accumulation, and the physiological conditions that trigger LD production, in response to various environmental factors.

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Phylogenetic and ecological analysis of novel marine stramenopiles.

Publications

Phylogenetic and ecological analysis of novel marine stramenopiles.

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