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

Les microbes évoluent rapidement en raison de temps de génération courts et de grandes tailles de population, ce qui les rend idéaux pour étudier l’évolution en laboratoire.La sélection naturelle agit sur les variantes allèles existantes dans la population, rendant les groupes aux variantes favorables plus abondants dans des environnements changeants.Par exemple, dans des conditions anaérobies, Rhodobacter utilise la lumière pour effectuer la photosynthèse, en utilisant les pigments bactériochlorophylle et caroténoïdes.Pendant une obscurité prolongée, les pigments de Rhodobacter ont peu d’avantages, favorisant les mutants dépourvus de pigment dans la population. Mais le type sauvage domine une fois la lumière revenue.Un autre exemple est l'« Expérience d’évolution à long terme » en cours. Elle a été créée en 1988 avec 12 populations identiques d’E. coli se développant dans un environnement limité en glucose.Depuis, cette expérience a suivi plus de 80 000 générations.Au fil du temps, une population d’E. coli a développé une mutation rare. Et cela a permis à cette population de métaboliser le citrate dans des conditions riches en oxygène.Cette mutation a donné accès à une nouvelle source de nutriments et un avantage concurrentiel sur leurs ancêtres.

Évolution de nouveaux traits chez les microbes

Les micro-organismes évoluent rapidement en raison de leur grande taille de population et de leurs temps de génération courts, présentant souvent des changements mesurables en quelques jours en conditions de laboratoire. La sélection naturelle agit sur la variation génétique permanente, permettant la conservation et l’amplification de traits bénéfiques qui confèrent des avantages en matière de fitness dans des environnements changeants.<h3>Régulation adaptative des pigments chez Rhodobacter</h3>Chez Rhodobacter, un genre de bactéries violettes non sulfurées, des pigments capteurs de lumière tels que la bactériochlorophylle et les caroténoïdes permettent la photosynthèse dans des conditions anaérobies et éclairées. L’expression de ces pigments est strictement régulée par l’oxygène et les niveaux lumineux de l’environnement afin de s’aligner sur l’activité photosynthétique.Cependant, dans l’obscurité, les pigments n’offrent aucun bénéfice fonctionnel et imposent plutôt un fardeau énergétique. En conséquence, des mutants dépourvus de ces pigments apparaissent et sont privilégiés dans des conditions sombres en raison de la réduction des coûts métaboliques. Néanmoins, lorsque la lumière redevient disponible, ces mutants déficients en pigment sont surpassés par des cellules sauvages capables de photosynthèse.Ce schéma de sélection réversible présente un compromis adaptatif, où les fluctuations environnementales déplacent l’équilibre entre efficacité métabolique et acquisition d’énergie.<h3>Expérience d’évolution à long terme chez E. coli</h3>Un autre exemple emblématique d’évolution microbienne est l’Expérience d’évolution à long terme (LTEE), initiée par Richard Lenski en 1988. Cette étude en cours a suivi des populations d’Escherichia coli cultivées dans un milieu limité en glucose pendant plus de 80 000 générations. Au fil du temps, ces lignées ont évolué diverses adaptations, notamment une augmentation de la taille cellulaire, des taux de croissance plus rapides et des voies métaboliques optimisées.<h3>Évolution de l’utilisation du citrate</h3>Plus particulièrement, une lignée a développé la capacité de métaboliser le citrate dans des conditions aérobies — un trait généralement absent chez E. coli de type sauvage, qui ne peut pas importer de citrate en présence d’oxygène. Cette innovation a permis à la souche mutante d’exploiter une ressource autrement inaccessible, obtenant ainsi un avantage sélectif significatif.Les analyses génétiques ont révélé que ce trait est apparu par une série de mutations — établissant initialement le potentiel d’utilisation du citrate (potentialisation), suivi de mutations permettant son expression et son transport réel (actualisation). Cette découverte met en lumière l’interaction entre la contingence, la mutation et la sélection naturelle dans l’innovation évolutive.Ensemble, ces études illustrent comment les systèmes microbiens servent de modèles dynamiques pour observer les processus évolutifs en temps réel. Ils mettent en avant à la fois des forces déterministes et des événements stochastiques qui stimulent la diversité biologique et l’innovation.

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

https://cloudfront.jove.com/files/ftp_upload/40722/40722_article_thumb_40722.jpg

Education

Enseignement

JoVE Core

Microbiology

Microbiologie

Unit

Unité

Microbial Evolution

Évolution microbienne

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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

Description

Transcript

Tags