Related Experiment Video
Updated: Aug 1, 2026
06:03
Procedure for Adaptive Laboratory Evolution of Microorganisms Using a Chemostat
Published on: September 20, 2016
Evolution of microbial genomes: sequence acquisition and loss.
1Department of Molecular Evolution, Uppsala University EBC, Norbyvagen 18C, SE-75236 Uppsala, Sweden. otto.berg@ebc.uu.se
Molecular Biology and Evolution
|November 26, 2002
Summary
Most novel microbial sequences are neutral and transient due to large population sizes. Only strongly selected sequences persist, influencing microbial genome evolution and speciation.
Area of Science:
- Microbial population genetics
- Evolutionary biology
- Genomics
Background:
- Understanding the dynamics of novel sequence acquisition and deletion is crucial for microbial evolution.
- Most novel sequences are inferred to be neutral, meaning they do not confer a selective advantage or disadvantage.
Purpose of the Study:
- To model the acquisition and deletion of novel sequences in microbial populations.
- To investigate the factors influencing the fixation and persistence of neutral and near-neutral sequences.
- To explore the mechanisms maintaining microbial genome size and driving speciation.
Main Methods:
- Development of models for homogeneous and island population structures.
- Application of a Moran model with overlapping generations to derive gene frequency distributions.
- Analysis of factors such as population size, mutation rates, and selection pressures.
Main Results:
- Novel, neutral sequences are unlikely to become globally fixed in large microbial populations.
- Microbial populations exhibit a high diversity of transient neutral gene content.
- Only sequences under strong selection are expected to persist long-term.
- Genome size may be maintained by a quasi-steady state of acquisition and deletion rates.
- Sequence loss plays a significant role in the divergence and speciation of microbial populations.
Conclusions:
- Microbial genome evolution is shaped by the interplay of neutral processes, selection, and population structure.
- Transient neutral sequences contribute to microbial diversity but do not drive long-term adaptation.
- Strong selection is the primary driver for the persistence of genetic elements.
- Mechanisms of gene gain and loss are key to genome size regulation and the emergence of new microbial lineages.
Related Concept Videos
03:21Genome Size and the Evolution of New Genes
While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.
03:21Genome Size and the Evolution of New Genes
While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.
01:26Evolutionary Processes in Microbes
Microbial evolution occurs rapidly due to short generation times and a variety of genetic processes, including horizontal gene transfer, mutation, recombination, and genetic drift. These mechanisms collectively enable microbes to adapt swiftly to changing environments.Horizontal gene transfer (HGT) allows genes to move between different species and occurs through three main mechanisms: conjugation, transformation, and transduction. Conjugation involves direct cell-to-cell contact for DNA...
01:24Evolution of New Traits in Microbes
Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...
01:08Evolution of Microbial Genome
Microbial genome evolution is a highly dynamic process shaped by continual gene gain and loss across species and strains. This genomic flexibility allows microorganisms to adapt rapidly to environmental pressures and interactions with other organisms. Central to understanding this diversity is the distinction between the core and pan genomes.The core genome comprises the genes shared by all sampled strains of a species, representing essential functions needed for fundamental cellular processes.
01:28Microbial Phylogeny
Understanding the evolutionary relationships among microorganisms is fundamental to microbial ecology and taxonomy. Phylogenetic trees are essential tools for inferring these relationships, relying primarily on comparative analyses of molecular sequences such as DNA, RNA, or proteins. In microbial studies, these trees typically depict the evolutionary paths of diverse bacterial and archaeal species by mapping genetic differences accumulated over time.Phylogenetic trees are composed of tips,...