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Bacteria Kingdom / Monera

Domain bacteria have only one kingdom, kingdom Bacteria are also known as kingdom Monera. Organisms that are classified under the bacteria kingdom are single-celled prokaryotic organisms.

Covering the cytoplasm there is a cell membrane, cell wall, and cell capsule. The cell wall is made of “Murine”.  Cell capsule is usually a polysaccharide structure. Bacteria contain two types of DNA; Bacterial chromosomes and Plasmids. Both are circular, double-stranded DNA molecules. Plasmids are small circular DNA molecules that are separate from bacterial chromosomes.

Bacteria Cell Structure
Figure 01: Bacteria Cell Structure

Plasmids can replicate independently.  Bacterial chromosomes are larger than plasmids, and it has all the information needed for the cell to survive. Reproduction of bacteria is by binary fission.

Classification of bacteria

Bacteria show different respiration types, different nutrition types, different shapes, etc. some bacteria have flagella which is a protein core. There is also a difference between bacteria in flagellation.

01. Classification of bacteria depend on the respiration

Bacteria are classified into four categories depending on their oxygen requirement for respiration.

Aerobic bacteriaBacteria grow only in oxygenated environments. They require oxygen for survival.Acetobacter

Gluconobacter
Anaerobic bacteriaAnaerobic bacteria grow only in oxygen-free environments. Oxygen is toxic for anaerobes.Clostridium
Facultative anaerobic bacteriaBacteria can grow both presence and absence of oxygen. When the presence of oxygen they use oxygen for respiration. With the absence of oxygen, they switch into fermentation.Lactobacillus

Escherichia coli
MicroaerophileMicroaerophiles need oxygen to survive but they grow at very lower concentrations of oxygen. typically, 2–10% O2Campylobacter
Classification of bacteria depends on the respiration

02.Classification of bacteria depend on nutrition

Bacteria can be divided into two main groups according to the source of the carbon used for nutrition.

I. Autotrophic bacteria

Autotrophic bacteria can produce their own food inside the cell. They use inorganic carbon / CO2 as the source of carbon. Autotrophic bacteria can be divided into two categories depending on the energy source that they use to produce food.

a. Photoautotrophic bacteria – they synthesize their own organic food by using CO2 and photo energy.

E.g.:  cyanobacteria, purple sulfur bacteria

b. Chemoautotrophic bacteria - They synthesize their own organic food by using CO2 and chemical energy.

E.g., Nitrosomonas, Nitrobacter

II. Heterotrophic bacteria

Heterotrophic bacteria cannot produce their own food. So, they use organic nutrition. (organic carbon). The heterotrophic bacteria can also be divided into two categories depending on their energy source.

a. Photoheterotrophic bacteria – bacteria that feed on organic compounds as the carbon source and the photo energy as the energy source.

E.g., purple non-sulfur bacteria

b. Chemoheterotrophic bacteria - bacteria that feed on organic compounds as the carbon source and chemical energy as the energy source.

E.g., Sulfur-oxidizing bacteria, Nitrogen-fixing bacteria, Iron-oxidizing bacteria.

03.Classification depends on the shape of bacteria

Bacteria are classified into five categories depending on their shape.

  1. Cocci – spherical shape bacteria.
  2. Bacilli – rod shaped bacteria.
  3. Spirilla – spiral bacteria
  4. Comma – comma shaped bacteria
  5. Spirochaetes – long helically coiled cells. They show wavy motions along the axis.
The classification depends on the shape of the bacteria
Figure 02: The classification depends on the shape of the bacteria

04.Classification depends on the type of cell wall

Depend on the type of the cell wall bacteria can be divided into two categories as gram-positive and gram-negative. Gram-positive bacteria have a thick peptidoglycan layer and no outer lipid membrane. Gram-negative bacteria have a thin layer of peptidoglycan and an outer lipid membrane.

Gram-positive bacteria give a positive result on a Gram-positive test and appear purple when seen through an optical microscope. Gram-positive bacteria retain the crystal violet stain while gram-negative bacteria do not retain the crystal violet stain used in the gram-gram staining method.

The classification depends on the type of cell wall
Figure 03: The classification depends on the type of cell wall


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References and Attributes

Sciencelearn.org - Bacterial DNA – the role of plasmids
Technologynetworks.com - Gram Positive vs Gram-Negative
Serc.carleton.edu - Gram Staining

Figures:

Cover Image was designed using an image by Arek Socha from Pixabay
Figure 01: Image by Clker-Free-Vector-Images from Pixabay
Figure 02: Image by LadyofHats, Public domain, via Wikimedia Commons


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