Classification of Microorganism CHAPTER 10

The study of the evolutiona ry history of organisms

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The science of classi fying organisms – Provides universal names for organisms – Provides a reference for identifying organisms

Archea and Bacteria

Ribotyping involves the fingerprinting of genomic DNA restriction fragments that contain all or part of the genes coding for the 16S and 23S rRNA. By digesting the genes with a specific restriction enzyme, fragments of different lengths are generated. By performing a Gel electrophoresis with the digested samples, the fragments can be visualised as lines on the gel, where larger fragments are close to the start of the gel, and smaller fragments further down. After blotting onto a matrix and probing, these lines form a unique pattern for each species and can be used to identify the origin of the DNA, almost like a barcode can identify a product. Conceptually, ribotyping is similar to probing restriction fragments of chromosomal DNA with cloned probes (randomly cloned probes or probes derived from a specific coding sequence such as that of a virulence factor).^[1]

The endosymbiotic theory states that several key organelles of eukaryotes originated as symbioses between separate single-celled organisms. According to this theory, mitochondria and plastids (e.g. chloroplasts), and possibly other organelles, represent formerly free-living bacteria that were taken inside another cell as an endosymbiont. Molecular and biochemical evidence suggest that the mitochondrion developed from proteobacteria (in particular, Rickettsiales, the SAR11 clade,^[1][2] or close relatives) and the chloroplast from cyanobacteria.

Each species retains some characteristics of its ancestor  Grouping organisms according to common properties implies that a group of organisms evolved from a common ancestor – Anatomy – Fossils – rRNA

-No peptidoglycan in cell wall -Not sensitive to antibiotics -Extreme environments -Methanogens -Extreme halophiles -Hyperthermophiles -May have histones

-Peptidoglycan in cell wall -Sensitive to antibiotics -All pathogenic and non- pathogenic bacteria -No histones

Eukaryotic species: A group of closely related organisms that breed among themselves

Prokaryotic species: A population of cells
with similar characteristics

Strain: A population of cells that genetically differs from other members of th e species. (identified by numbers, letters or names after the specific epithet.) – Clone: Population of cells derived from a single cell

Viral species: Population of viruses with similar characteristics that occupies a particular ecological niche [Species have at least 97% similarity in rRNA se q uence. ]

A genus is a taxon comprised of one or more species and below family. Greater than 93% similarity in 16S rRNA share a genus

Common names – Vary with languages – Vary with geography  Binomial Nomenclature (genus + specific epithet) – Used worldwide Escherichia coli Homo sapiens

Classification: to determine the taxonomic category of a newly isolated organism. Applies to newly discovered organisms. Identification: to identify an isolated organism by comparing its characteristics. Applies to organisms already known and classified