Biodiversity and environmental distribution of apusozoan Protozoa and the deep phylogeny of bikont eukaryotes

无胞原生动物的生物多样性和环境分布以及双体真核生物的深层系统发育

• 批准号: NE/E004156/1
• 负责人: Thomas Cavalier-Smith
• 金额: $ 43.33万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE004156%2F1
• 关键词: Biodiversity; environmental; distribution; apusozoan; Protozoa

Protozoa are single-celled organisms very abundant in all environments. Unlike bacteria, they possess a nucleus, making them part of eukaryotes, the group of living organisms to which multicellular plants, fungi, and animals belong. Morphological and molecular studies (based on comparing gene sequences from different organisms) allow the division of Protozoa into 11 main groups (phyla). Most of these phyla can be placed in one of 6 major assemblages of eukaryotes, three of which contain only protozoans. The species diversity, abundance and ecological significance of the different protozoan phyla are highly variable but can be difficult to assess directly. In some phyla very many species are known, and as they are abundant and/or easy to distinguish morphologically, their presence or absence can readily be ascertained in different habitats. In other phyla only a few species have been described perhaps because they possess very few distinguishing morphological characters, and virtually nothing is known of their ecology. Are the latter phyla truly species-poor and their members rare? Or is this an artefact due to a lack of interest in the group or the paucity of available characters for distinguishing species? We can now answer these questions using molecular methods to check the presence or absence and diversity of selected groups of organisms in different habitats using group-specific genetic probes based on known gene sequences. Apusozoa is a recently defined phylum that not yet been given much attention because it lacks obvious medical or economic importance and comprises very poorly studied lineages of protozoans. However, they could be considerably more diverse than is currently realised and Amastigomonas is known to be a very ancient cell type, older than the whole animal kingdom, and very widespread in marine sediments as are some other Apusozoa. Few apusozoan species are known, and there is uncertainty about the evolutionary unity of the phylum: 5 or 6 probably equally ancient lineages of protozoans may belong to this phylum. Apusozoa are of particular interest for two reasons. First, they are a perfect model group to test the utility of cultivation-independent, molecular approaches for ecological inferences. The species diversity and ecological importance of Apusozoa are extremely poorly known. We will use specific genetic probes to amplify pieces of the gene encoding ribosomal RNA (widely used for genetic comparisons) to determine (1) how many distinct genetic types can be defined in each lineage, (2) in which habitats the different apusozoan lineages can be found, and (3) whether some lineages or species may be specific to a given habitat. Specific genetic probes matching new genotypes will also be used to try and isolate from the sampled habitat and culture the organisms to which the gene sequences belong. We will obtain large numbers of sequences from protein-coding genes to test whether mutations in these genes are being recombined by sexual reproduction as in higher organisms, or whether instead these Apusozoa are non-sexual like bacteria. We will also use these protein sequences to decide whether each cell has one copy only of the genome or two (like animals) and whether they have acquired novel genes from the DNA of their food. The second and key interest of Apusozoa is their pivotal importance for understanding the evolution of eukaryotes as a whole. Ribosomal RNA comparisons imply that they do not belong to any of the six major assemblages of eukaryotes defined up to now. Rather, they might form an independent group very close to the last common ancestor of all eukaryotes. Using over 100 protein gene sequences, we will also construct a better evolutionary tree independent of that from ribosomal RNA to determine more precisely whether the different lineages that have been suggested to belong to Apusozoa truly form a coherent evolutionary unit, and what their exact relationships are to other eukaryotes.

原生动物是在所有环境中都非常丰富的单细胞生物。与细菌不同，它们拥有细胞核，使它们成为真核生物的一部分，真核生物是多细胞植物、真菌和动物所属的活生物体群体。形态学和分子研究（基于比较不同生物体的基因序列）将原生动物分为 11 个主要类群（门）。这些门中的大多数可以归入真核生物的 6 个主要组合之一，其中三个仅包含原生动物。不同原生动物门的物种多样性、丰度和生态意义差异很大，但很难直接评估。在一些门中，已知有非常多的物种，并且由于它们丰富和/或易于在形态上区分，因此可以在不同的栖息地中容易地确定它们的存在或不存在。在其他门中，只有少数物种被描述，也许是因为它们几乎没有显着的形态特征，而且实际上对其生态学一无所知。后一门真的是物种匮乏且成员稀有吗？或者这是由于对该群体缺乏兴趣或缺乏可用于区分物种的特征而造成的人为现象？我们现在可以使用分子方法来回答这些问题，以使用基于已知基因序列的群体特异性遗传探针来检查不同栖息地中选定生物群体的存在或不存在及其多样性。 Apusozoa 是最近定义的一个门，尚未受到太多关注，因为它缺乏明显的医学或经济重要性，并且包含研究很少的原生动物谱系。然而，它们可能比目前意识到的更加多样化，并且已知无鞭毛虫是一种非常古老的细胞类型，比整个动物界更古老，并且与其他一些无毛虫一样广泛存在于海洋沉积物中。已知的无背动物种类很少，并且该门的进化统一性也存在不确定性：5或6个可能同样古老的原生动物谱系可能属于该门。由于两个原因，Apusozoa 受到特别关注。首先，它们是一个完美的模型组，可以测试独立于培养的分子方法在生态推论中的效用。人们对阿普索动物的物种多样性和生态重要性知之甚少。我们将使用特定的遗传探针来扩增编码核糖体 RNA 的基因片段（广泛用于遗传比较），以确定（1）每个谱系中可以定义多少种不同的遗传类型，（2）可以在哪些栖息地中发现不同的无足动物谱系，以及（3）某些谱系或物种是否可能特定于给定的栖息地。与新基因型相匹配的特定基因探针也将用于尝试从采样的栖息地中分离并培养该基因序列所属的生物体。我们将从蛋白质编码基因中获得大量序列，以测试这些基因的突变是否像高等生物一样通过有性繁殖进行重组，或者这些无性动物是否像细菌一样是无性生殖的。我们还将使用这些蛋白质序列来确定每个细胞是否只有一个基因组副本或两个（如动物），以及它们是否从食物的 DNA 中获得了新基因。 Apusozoa 的第二个也是关键的兴趣是它们对于理解整个真核生物的进化至关重要。核糖体 RNA 比较表明它们不属于迄今为止定义的六种主要真核生物组合中的任何一种。相反，它们可能形成一个非常接近所有真核生物最后共同祖先的独立群体。利用超过100个蛋白质基因序列，我们还将构建一个更好的独立于核糖体RNA的进化树，以更精确地确定被认为属于Apusozoa的不同谱系是否真正形成一个连贯的进化单位，以及它们与其他真核生物的确切关系。

项目成果

Correction to 'Origin of animal multicellularity: precursors, causes, consequences-the choanoflagellate/sponge transition, neurogenesis and the Cambrian explosion'

对“动物多细胞性的起源：前体、原因、后果——领鞭毛虫/海绵转变、神经发生和寒武纪爆发”的更正

• DOI: 10.1098/rstb.2017.0001
• 发表时间: 2017
• 期刊: Biological Sciences
• 作者: Cavalier-Smith T

Vendozoa and selective forces on animal origin and early diversification: reply to Dufour and McIlroy (2017).

• DOI: 10.1098/rstb.2017.0336
• 发表时间: 2018-01-19
• 期刊: Philosophical transactions of the Royal Society of London. Series B, Biological sciences
• 作者: Cavalier-Smith T

Euglenoid pellicle morphogenesis and evolution in light of comparative ultrastructure and trypanosomatid biology: Semi-conservative microtubule/strip duplication, strip shaping and transformation.

根据比较超微结构和锥虫生物学的眼虫膜形态发生和进化：半保守微管/条带复制、条带成形和转化。

• DOI: 10.1016/j.ejop.2017.09.002
• 发表时间: 2017
• 期刊: European journal of protistology
• 影响因子: 2.9
• 作者: Cavalier-Smith T