Microbial Evolution and Systematics - Classification and Nomenclature

7 important questions on Microbial Evolution and Systematics - Classification and Nomenclature

What is the significance of comparative genomics, and what does it reveal about microbial genomes?

Comparative genomics uses whole genome sequencing technologies to analyze differences in gene content and DNA sequence composition across sets of genomes. It reveals that microbial genomes are highly diverse and dynamic, with individual strains within a species differing significantly in gene composition.

Explain the concept of the core genome and pan genome in microbial species, using Salmonella enterica as an example.

he core genome consists of genes shared by all individual strains of a species, while the pan genome includes the core genome plus genes not shared by all strains. In Salmonella enterica, all strains share 2811 core genes, but each strain also has a unique set of strain-specific genes, illustrating the diversity within the pan genome.

How does the dynamic nature of microbial genomes manifest in Escherichia coli, and what is the core genome's role?

The genomes of different Escherichia coli strains vary substantially, with only 39% of genes shared among all strains. E. coli genomes have an average of 4721 genes, but the core genome, consisting of genes present in all strains, is much smaller (1976 genes). The core genome is crucial for defining the species, while the pan genome reflects strain-specific genes acquired through horizontal gene transfer.
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What factors influence the size of the core genome in Escherichia coli?

The size of the core genome in Escherichia coli can be expected to decrease as the evolutionary distance of strains increases. As new strains are sequenced, the number of unique genes and the size of the pan genome continue to increase, highlighting the ongoing acquisition of genes through horizontal gene transfer.

What is the concept of chromosomal islands, and how do they contribute to microbial genome evolution?

Chromosomal islands are clusters of genes for specialized functions acquired through horizontal gene transfer. They are often flanked by inverted repeats, have distinct base composition and codon bias, and belong to the pan genome. Chromosomal islands play a crucial role in microbial genome evolution by allowing the acquisition of entire genetic pathways, including those for virulence factors, symbiosis, or pollutant degradation.

What are pathogenicity islands, and how are they related to chromosomal islands in pathogenic bacteria like Escherichia coli?

Pathogenicity islands are chromosomal islands that encode virulence factors in pathogenic bacteria. In Escherichia coli, uropathogenic strains contain pathogenicity islands associated with adhesins and capsules that facilitate infections. These islands are often transferred between cells by mechanisms like transduction, contributing to the pathogenicity of certain strains.

Provide examples of functions encoded by chromosomal islands other than virulence factors.

Chromosomal islands can encode functions beyond virulence factors. Examples include genes for degrading pollutants such as aromatic hydrocarbons and herbicides. Additionally, genes essential for the symbiotic relationship between nitrogen-fixing bacterium Rhizobium and plant root nodules are carried in chromosomal islands. The magnetosome island of Magnetospirillum is unique, carrying genes for intracellular magnetic particles.

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