Topic 1 - BACTERIAL CLASSIFICATION SCHEMES

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Topic contentCharacterisation of speciesBinomial systemProblems of classificationPhylogenetic classification

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Characterisation Why?..Great number and diversity of

organisms.Classification: Grouping of related organism together.Many m/o look alike to be classified

according to the structureLiterally hundreds of bacterial species are

small rods or small cocci.

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Figures 4.1a, 4.2a, 4.2d, 4.4a, 4.4b, 4.4c

Basic ShapesBacillus (rod-shaped) Coccus (spherical)Spiral

SpirillumVibrioSpirochete

Arrangements

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Figure 4.7a

Prokaryotic Cells: ShapesAverage size: 0.2 –1.0 µm 2 – 8 µmMost bacteria are monomorphicA few are pleomorphic

Figure 4.6

The Cell WallPrevents osmotic lysisMade of peptidoglycan (in bacteria)

Gram-Positive Bacterial Cell Wall

Figure 4.13b

Gram-Negative Bacterial Cell Wall

Figure 4.13c

Thick peptidoglycanTeichoic acids

Gram-positiveCell Wall

Figure 4.13b–c

Thin peptidoglycan Outer membrane Periplasmic space

Gram-positiveCell Wall

Motile CellsRotate flagella to run or tumbleMove toward or away from stimuli (taxis)Flagella proteins are H antigens

(e.g., E. coli O157:H7)

Figure 4.7

Arrangements of Bacterial Flagella

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History of Binomial NomenclatureFather of taxonomy?Two name system,Latin scientific name.Formal system of naming organismsOrganizing,classifying and naming organisms

into groups-according to the specific criteria.How to write these names??Vibrio choleraeStaphylococcus spE.coli

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Genus and species Genus - capitalized species – specific epithet.

Example: Escherichia coli,E.coli

• Information gained: shape,who discovered,where it is found,what disease they cause.

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General problemsEstablishing a standard names for organisms

so that we can communicate about themUsually classified according to their

phylogenetic or evolutionary, but not always easy

Leads to introduction of a dichotomous key

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Dichotomous keyHas paired statements describing

characteristic of organismsPaired statement can only have one

statement trueEach paired statement relate to each other

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Figure 10.8

Dichotomous Key

Reasons causing problems1. Deciding what constitutes a species –

because of some bacteria have the similar characteristics so taxonomist try to tolerate the organism within species

2. Deciding what constitutes a kingdom – because most of organism having sexually reproduction so have very factors affecting the variable of the characteristics

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Focusing on bacterial classificationOther organism categorized from domain to

species, but for prokaryotic cell, start from strain to genus

However facing problems reaching the classes and orders level

Wide range of studies needed on identification and building up taxonomy of bacteria

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Phylogenetic hierarchyGrouping organism according to common properties that implies that a group of organisms evolved from common ancestors.

Each species retains some characteristics of the ancestor.

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Hierarchy domain – Bacteriakingdom – none assign for bacteriaphylum – Proteobacteriaclass – Gamma-proteobacteriaorder – Enterobacterialesfamily – Enterobacteriaceagenus – EschericiaSpecies – E.coli

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start

Three domain system classification

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Terminologies (answer)Taxa – subdivisions used to classify organism:

domain, kingdom, phylumPhylogeny / sytematic – the evolutionary

history of a group of organism; phylogenetic relationships are evolutionary relationship

Taxonomy – the science of the classification of organism

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The enD

Short lecture ,but!!!MAKE MORE revision on it….

TQ

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