Name: microbial adaptation in changing environments
Uploaded: 2026-03-12T13:57:34.000Z
Duration: 1 min 24 s
Channel: JoVE

微生物は短い世代と大きな個体群のため急速に進化し、実験室での進化研究に理想的です。自然選択は集団内の既存の対立遺伝子変異に作用し、変化する環境の中で有益な変異を持つグループをより多く見せます。例えば、嫌気性条件下では、 ロドバクテrは光を利用して光合成を行い、色素のバクテリオクロロフィルとカロテノイドを用います。長時間の暗闇の間、 ロドバクターの 色素はほとんど効果がなく、個体群の色素を欠く変異体を有利に働きます。しかし、光が戻ると野生型が支配的になります。もう一つの例は、現在進行中の「長期進化実験」です。1988年に、グルコース制限環境で同一の 大腸菌 12個体群が成長して始まりました。それ以来、この実験は8万世代以上を追跡しています。時が経つにつれ、ある 大腸菌 集団は珍しい変異を得ました。そして、この集団は酸素豊富な環境でクエン酸塩を代謝することができました。この突然変異は新たな栄養源へのアクセスと祖先に対する競争優位をもたらしました。

微生物における新しい形質の進化

微生物は個体群が大きく、世代が短いため急速に進化し、実験室条件下で数日以内に測定可能な変化を示すことが多いです。自然選択は既存の遺伝的変異に作用し、変化する環境下での適応度の利点をもたらす有益な形質を保持・増幅させることを可能にします。<h3> ロドバクターにおける適応的色素調節</h3>紫色の非硫黄細菌の属である ロドバクターでは、バクテリオクロロフィルやカロテノイドなどの光収集色素が嫌気性の照明条件下での光合成を可能にします。これらの色素の発現は、環境の酸素や光のレベルによって厳密に調節され、光合成活動と整合します。しかし暗闇では、顔料は機能的な効果をもたらさず、むしろエネルギー的な負担となります。その結果、これらの色素を欠く変異体が出現し、代謝コストが低い暗い環境で好まれます。しかし、光が再び現れると、これらの色素欠乏変異体は光合成能力を持つ野生型細胞に圧倒されます。この可逆的選択のパターンは、環境の変動によって代謝効率とエネルギー獲得のバランスが変わる適応的なトレードオフを示しています。<h3>大腸菌の長期進化実験 </h3>微生物進化のもう一つの代表的な例は、1988年にリチャード・レンスキーによって開始された長期進化実験(LTEE)です。この進行中の研究では、グルコース制限培地で培養された 大腸菌 集団を8万世代以上追跡しています。これらの系統は時間とともに、細胞サイズの増加、成長速度の加速、代謝経路の最適化など、さまざまな適応を進化させてきました。<h3>シトレート利用の進化</h3>特に、ある系統は好気条件下でクエン酸を代謝する能力を進化させました。これは、酸素が存在する場合クエン酸を運べない野生型大 腸菌には通常存在しない特徴です。この革新により、変異株は通常アクセス困難な資源を利用でき、大きな選択的優位性を得ました。遺伝学的解析により、この形質は一連の突然変異によって生じることが明らかになりました。最初はシトレート利用(増強)の可能性が確立され、その後、その発現と輸送(実現)を可能にする突然変異が続きました。この発見は、偶然性、突然変異、自然選択が進化の革新における相互作用を浮き彫りにしています。これらの研究は、微生物システムが進化過程をリアルタイムで観察する動的モデルとして機能していることを示しています。それらは決定論的な力と、生物多様性とイノベーションを推進する確率的な出来事の両方を示しています。

Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under ...

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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

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 without waiting for brand-new mutations.

One example is Rhodobacter, a group of purple non-sulfur bacteria. These cells use light-harvesting pigments such as bacteriochlorophyll and carotenoids to support photosynthesis when oxygen is low and light is available. Their pigment production is tightly controlled by oxygen and light levels.

In darkness, those pigments no longer help the cells. They also cost energy to make and maintain. Because of that cost, mutants that lose the pigments can be favored in the dark. When light returns, wild-type cells that can photosynthesize again outcompete the pigment-deficient mutants. This is a reversible selection pattern that shows a trade-off between saving energy and capturing light.

A second major example is the Long-Term Evolution Experiment, or LTEE, started by Richard Lenski in 1988. The study has followed Escherichia coli grown in a glucose-limited medium for more than 80,000 generations. Over time, these lineages evolved changes such as larger cell size, faster growth, and better metabolic pathways.

The best-known LTEE result is one lineage that gained the ability to use citrate under aerobic conditions. Wild-type E. coli usually cannot import citrate when oxygen is present, so this trait opened access to a new food source. Genetic analysis showed that the trait appeared through a series of mutations. First came potentiation, which created the potential for citrate use. Then later mutations enabled actualization, or the real expression and transport of citrate.

Together, these microbial studies show evolution in real time. They highlight how mutation, natural selection, chance, and environmental change can work together to create new traits and shape biological diversity.

Microbial Adaptation in Changing Environments

microbial-adaptation-in-changing-environments

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 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

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

See how microbes adapt through natural selection, pigment changes in Rhodobacter, and the E. coli LTEE, including the evolution of citrate use.

Microbial Adaptation in Changing Environments | 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

Microbial Adaptation in Changing Environments

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