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

Uma árvore filogenética representa relações evolutivas entre microrganismos e frequentemente depende de DNA, RNA ou sequências de proteínas.Nos filogramas, espécies aparecem nas pontas, e o comprimento dos galhos reflete a quantidade de mudança na sequência.Árvores enraizadas marcam ancestrais comuns e pontos de divergência, enquanto árvores sem raízes apresentam vínculos sem direção evolutiva.Árvores filogenéticas usam sequências homólogas, especialmente ortólogos, que são genes homólogos separados por especiação.Genes de subunidade rRNA pequena altamente conservada, como o gene 16S rRNA, servem como marcadores universais para comparações microbianas.O DNA desses genes marcadores nas amostras é sequenciado.As sequências são alinhadas para identificar descompassos e lacunas causadas por inserções ou deleções.Então, a distância evolutiva é medida como a razão entre as diferenças de nucleotídeos e o número total de posições alinhadas.Árvores filogenéticas às vezes podem ser enganosas quando características semelhantes evoluem independentemente ou quando a transferência horizontal de genes introduz genes através de linhagens não relacionadas, produzindo histórias genéticas que não refletem a história evolutiva real dos organismos.

filogenia microbiana

Compreender as relações evolutivas entre microrganismos é fundamental para a ecologia microbiana e a taxonomia. Árvores filogenéticas são ferramentas essenciais para inferir essas relações, baseando-se principalmente em análises comparativas de sequências moleculares como DNA, RNA ou proteínas. Em estudos microbianos, essas árvores normalmente representam os caminhos evolutivos de diversas espécies bacterianas e arqueias ao mapear diferenças genéticas acumuladas ao longo do tempo.Árvores filogenéticas são compostas por pontas, galhos e nós. As pontas representam espécies atuais ou amostradas, enquanto os ramos traçam trajetórias evolutivas. Os comprimentos dos ramos são proporcionais ao número de alterações genéticas inferidas entre os nós. Árvores enraizadas destacam um ancestral comum e divergência direcional, enquanto árvores sem raízes apenas mostram a parentesco sem assumir um ponto de origem. Nós internos representam formas ancestrais hipotéticas e podem marcar eventos de especiação ou divergência.Na filogenética microbiana, genes altamente conservados — particularmente o RNA ribossomal subunitário pequeno (RNA SSU) — são comumente usados devido à sua presença em todos os domínios da vida e à lenta taxa evolutiva. Esses marcadores genéticos universais permitem comparações entre amplas distâncias filogenéticas. Genes homólogos, e preferencialmente ortologos, são selecionados para a construção em árvores, garantindo que as sequências compartilhem uma ancestralidade e função comuns. Os ortólogos são tipicamente identificados usando buscas recíprocas de best-hit (por exemplo, BLAST) ou pipelines ortológicos, e então amplificados por meio de primers específicos do locus (ou enriquecimento direcionado) entre táxons. Os amplicões ou fragmentos enriquecidos resultantes são então sequenciados (frequentemente usando plataformas de alta produtividade) e filtrados pela qualidade. Essas sequências são alinhadas para detectar substituições, inserções ou deleções em posições homólogas. As distâncias evolutivas são quantificadas pelo grau de divergência de sequência.Embora as árvores filogenéticas ofereçam insights críticos, elas podem nem sempre refletir histórias evolutivas verdadeiras. Transferências horizontais de genes podem levar a semelhanças enganosas. Para resolver isso, métodos como a parcimônia máxima avaliam alinhamentos de sequência para inferir árvores que exigem menos mudanças evolutivas. Outras abordagens, como a máxima verosimilhança e a inferência bayesiana, também são comumente usadas para a construção de árvores e frequentemente fornecem modelos de evolução estatisticamente mais robustos.

Filogenia microbiana

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

Microbiologia

Unit

Unidade

Microbial Evolution

Evolução Microbiana

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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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