Shapes and Arrangement of Bacteria

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The shapes and arrangement of bacteria is called as Bacterial Morphology. The shapes and arrangement of bacteria is used for bacterial classification.

The Bacteria are unicellular and Prokaryotic cells. They lack nucleus and membrane bound organelles. Due to the microscopic size of the cells, we cannot observe them by naked eyes. We need microscopes to study and observe them. Whenever we observe them under microscope, we observe their cell shape, arrangement and size. The study of of bacterial shape, size and arrangements of cells is called as Bacterial Morphology.

The bacterial population can distinguished on the basis of physical appearance and hence it is the primary method used for bacterial classification.  The difference is shape and size may be due to the difference in habitat, ecology and genetic material.

Bacterial Morphology:

Shape and arrangement of the bacteria:

The most common bacterial shapes that have been observed are spherical, rod like, comma, wavy or spiral shape. The scientists have named such shapes as coccus, bacillus, vibrio, spiral and spirochete respectively. 

Spherical Shape:

The bacteria appears in circular shape. it is called as coccus (in singular) or cocci in plural.

Arrangement of Spherical bacteria

ArrangementDiagramExamples
Diplococci – Two cocci in pairDiplococciMoraxella catarrhalis, Neisseria gonorrhpeae
Tetracocci – four cocci arranged in cube like structureTetracocciAerococcus, Pediococcus
Staphylocci – cocci arranged in grapelike clusterStaphylococciStaphylococcus aureus
Sarcina – cubical packets of 8 cell in 3 planesSarcinaSarcina ventruculi, Sarcina ureae
Spherical shapes of Bacteria

Rod Shape:

The Bacteria appear in rod shape

Arrangement of rod shape bacteria –

ArrangementDiagramExamples
Diplobacilli – two bacilli in pairDiplobacilliCoxiella burnetti, Moraxella bovis, Klebsiella rhinoscleromatis
Streptobacilli – Bacilli are arranged in chainsStreptobacilliStreptobacillus moniliformis
Coccobacilli – short and stumpy, appear like ovoidCoccobacilliHaemophilus influenzae, Gardnerella vaginalis and Chlamydia trachomatis
Palisades – fencing like structurePalisadesCorynebacterium diptheriae
Rod shape Bacteria

Other shapes of bacteria:

Bacteria are also found in shapes other than spherical and rod.

ShapesArrangementDiagramExamples
CommaVibriosVibrioVibrio cholerae
Wavy or spiral (flexible)SpirillaSpirillaCampylobacter jejuni, Helicobacter pylori, Spirillum winogradskyi
Wavy or spiral (rigid)SpirochetesSpirochetesLeptospira interrogans, Treponema pallidum, Borrelia recurrentis
Variable shape – cannot define the shapePleomorphicMycoplasma genitalium
Other shapes of Bacteria

Conclusion:

The bacteria are found in different shapes and arrangement. Their physical appearance information is used for bacterial classification.

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