Name: reading microbial family trees
Uploaded: 2026-03-12T13:57:34.000Z
Duration: 1 min 28 s
Channel: JoVE

系統樹は微生物間の進化的関係を表し、多くの場合DNA、RNA、またはタンパク質配列に依存します。系統図では、種は先端に現れ、枝の長さは配列の変化の量を反映しています。根のある木は共通の祖先や分岐点を示し、根のない木は進化的な方向性のないつながりを示します。系統樹は特にホモログ配列を用い、これは種分化によって分離された相同遺伝子です。16S rRNA遺伝子のような高度に保存された小型サブユニットrRNA遺伝子は、微生物比較の普遍的なマーカーとして機能します。サンプル中のこれらのマーカー遺伝子のDNAはシーケンスされます。配列は、挿入や欠失による不一致やギャップを特定するためにアラインメントされます。次に、進化距離は塩基差と整列位置の総数の比率として測定されます。系統樹は、類似した形質が独立して進化する場合や、水平的な遺伝子移動によって無関係な系統間で遺伝子が導入され、実際の進化史を反映しない遺伝子履歴が生じる場合、誤解を招くことがあります。

微生物系統発生

微生物間の進化的関係を理解することは、微生物生態学および分類学において不可欠です。系統樹はこれらの関係を推測する重要なツールであり、主にDNA、RNA、タンパク質などの分子配列の比較解析に依存しています。微生物学の研究では、これらの樹木は通常、時間をかけて蓄積された遺伝的差異をマッピングすることで、多様な細菌や古細菌種の進化経路を描写します。系統樹は先端、枝、節で構成されています。先端は現存またはサンプル化された種を表し、枝は進化の軌跡をたどっています。枝の長さは、ノード間で推定される遺伝的変化の数に比例します。根のある木は共通の祖先と方向の発散を強調し、根のない木は原点を仮定せずに単に関連性を示します。内部ノードは仮想的な祖先形態を表し、種分化や分岐の出来事を示すことができます。微生物系統学において、特に小サブユニットリボソームRNA(SSU rRNA)など、高度に保存された遺伝子が一般的に用いられます。これは、生命のすべての領域に存在し、進化速度が遅いためです。これらの普遍的な遺伝マーカーにより、広範な系統学的距離を超えた比較が可能になります。系統樹構築には、配列が共通の祖先と機能を持つことを確実にするために、相同、できれば直系遺伝子が選択されます。オルソログは通常、相互ベストヒット検索(例:BLAST)や正書学パイプラインを用いて同定され、その後、遺伝子座特異的プライマー(または標的的濃縮)によって分類群全体で増幅されます。得られた増幅コンまたは濃縮された断片は、(多くの場合高スループットプラットフォームを用いて)シーケンスされ、品質フィルタリングされます。これらの配列は、相同位置での置換、挿入、欠失を検出するために整列されます。進化距離は配列の分岐度によって定量化されます。系統樹は重要な洞察を提供しますが、必ずしも真の進化の歴史を反映しているとは限りません。水平遺伝子移転は誤解を招く類似性を生むことがあります。これに対処するために、マキシマム・パシモニーのような手法は、最も進化的変化を最小限に必要とする系統樹を推定するために配列アライメントを評価します。最尤法やベイズ推論などの他の手法も木構造に一般的に用いられ、より統計的に堅牢な進化モデルを提供することが多いです。

Understanding the evolutionary relationships among microorganisms is fundamental to microbial ecology and taxonomy. Phylogenetic trees are essential tools ...

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Education

JoVE Core

Microbiology

微生物学

Unit

ユニット

Microbial Evolution

微生物の進化

KEY TERMS AND CONCEPTS

主要用語と概念

Microbial Phylogeny

reading microbial family trees

Reading microbial family trees helps scientists study how microorganisms are related. These trees are important in microbial ecology and taxonomy. They use molecular sequences such as DNA, RNA, or proteins to compare bacteria and archaea and trace genetic changes over time.

A phylogenetic tree has tips, branches, and nodes. The tips are the species that are sampled or still alive. The branches show evolutionary paths, and branch length reflects the number of genetic changes between nodes. Rooted trees show a common ancestor and a direction of divergence, while unrooted trees show relatedness without naming an origin point. Internal nodes stand for hypothetical ancestors and can represent speciation or other divergence events.

Microbial phylogenetics often relies on highly conserved genes. Small subunit ribosomal RNA, or SSU rRNA, is a common marker because it is found across all domains of life and changes slowly. These universal markers make it possible to compare organisms that are very far apart on the evolutionary tree. Researchers choose homologous genes, and preferably orthologous genes, so the sequences share common ancestry and function.

To build a tree, scientists first identify orthologs with reciprocal best-hit searches such as BLAST or with orthology pipelines. They then use locus-specific primers or targeted enrichment to amplify the genes across taxa. The resulting amplicons or enriched fragments are sequenced, often with high-throughput platforms, and quality-filtered before analysis.

Next, the sequences are aligned so scientists can spot substitutions, insertions, and deletions at matching positions. Evolutionary distance is estimated from how much the sequences differ. Even so, a tree may not always show the true history of a group, because horizontal gene transfer can create misleading similarities. To reduce that problem, scientists may use maximum parsimony, which chooses the tree with the fewest changes. Maximum likelihood and Bayesian inference are also common methods, and they often give more statistically robust models of evolution.

Reading Microbial Family Trees

origin of cellular life

How Early Cells Got Their Start

Early cellular life began under the harsh conditions of early Earth, where simple chemicals could form more complex organic molecules. Experimental evidence supports the idea that RNA nucleotides, amino acids, and lipids could arise spontaneously in this environment. Volcanic activity, strong UV radiation, and an atmosphere with little or no free oxygen likely helped drive these reactions. Hydrothermal vents on the ocean floor are considered one likely setting for the first life forms. These...

origin of photosynthesis

How Photosynthesis Changed Earth

Photosynthesis changed Earth’s atmosphere and made complex life possible. It began about 3.4 to 3.8 billion years ago, when the first photosynthetic organisms used light energy to build organic compounds. These early organisms were anoxygenic phototrophs, which means they made food from light but did not release oxygen. Early photosynthesis used hydrogen sulfide (H2S) or ferrous iron (Fe2+) as electron donors instead of water. Because of that, it did not produce molecular oxygen (O2) as a...

evolutionary processes in microbes

How Microbes Gain New Traits

Microbes gain new traits through fast genetic change. Their short generation times help evolution happen quickly. Mutation, horizontal gene transfer, recombination, and genetic drift all contribute to this process. Together, these mechanisms help microbial populations adjust to changing environments. Horizontal gene transfer, or HGT, moves genes between different species. It happens in three main ways: conjugation, transformation, and transduction. Conjugation requires direct cell-to-cell...

evolution of new traits in microbes

Microbial Adaptation in Changing Environments

Microbial adaptation in changing environments can happen very quickly. Microorganisms often evolve fast because they have large population sizes and short generation times. In the lab, these changes can sometimes be measured within days. Natural selection acts on standing genetic variation, which is the genetic diversity already present in a population. When conditions change, helpful traits can be kept and increased because they improve fitness. This lets microbes respond to new pressures...

evolution of microbial genome

Microbial Core and Pan-Genome Changes

Microbial genomes change through gene gain and gene loss. These changes help microbes adapt to new environments and to other organisms they live with. In many species, genome evolution is fast and ongoing. A key idea is the difference between the core genome and the pan-genome. The core genome is the set of genes shared by all sampled strains of a species. These genes support basic cell functions. For example, Salmonella enterica has about 2,800 core genes, although the exact number can change...

microbial phylogeny

Reading microbial family trees helps scientists study how microorganisms are related. These trees are important in microbial ecology and taxonomy. They use molecular sequences such as DNA, RNA, or proteins to compare bacteria and archaea and trace genetic changes over time. A phylogenetic tree has tips, branches, and nodes. The tips are the species that are sampled or still alive. The branches show evolutionary paths, and branch length reflects the number of genetic changes between nodes.

phylogenetic species concept in microbiology

phylogenetic-species-concept-in-microbiology

How DNA Defines Microbial Species

The phylogenetic species concept helps define microbial species by looking at DNA and evolutionary relatedness. It focuses on shared ancestry and genetic traits that can be diagnosed in different organisms. This approach is especially useful in microbiology, where other species concepts often do not work well. Traditional morphological and biological species concepts rely on body form or reproduction. Those methods can fall short for microbes because many reproduce asexually, show little...

key terms and concepts

Learn how microbial phylogenetic trees use DNA, RNA, and protein sequences to show relationships among bacteria and archaea, and how scientists build them.

Reading Microbial Family Trees | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Reading Microbial Family Trees

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