Structure, Classification And Reproduction of Eubacteria

Eubacteria are also known as “True bacteria,” are among the oldest and most diverse organisms on our planet. Eubacteria are prokaryotic organisms, lacking a nucleus and membrane-bound organelles. Eubacteria differ from another group of prokaryotes called Archaea due to differences in their biochemical characteristics. Eubacteria can be found in various environments, including soil, water, the human gut, and even in extreme conditions. They belongs to the kingdom Monera.

Characteristics of Eubacteria

1. Eubacteria are single-celled or unicellular prokaryotic organisms.
2. Eubacteria have rigid cell wall made of peptidoglycans, which maintain the cell integrity and shape.
3. The cell membrane composed of a bilayer of phospholipids together with proteins.
4. They have flagella which help in locomotion.
5. They lack mitochondria and chloroplast.
6. Numerous eubacteria produce spores.
7. Eubacteria mostly reproduce asexually by binary fission.
8. Eubacteria can be photosynthetic autotophic produce food through photosynthesis or chemosynthentic autotophic oxidise inorganic subsatnces, or heterotrophic .
9. They vary in forms such as spirillia, bacilli, or cocci.

Structure of bacteria

• Cell Wall: It is made of peptidoglycan, which provides rigidity and shape. It determines whether the bacterium is Gram-positive or Gram-negative.
• Cell Membrane: Lies beneath the cell wall and controls the movement of substances in and out.
• Cytoplasm: A gel-like matrix composed of water, enzymes, nutrients, and other molecules. It contains ribosomes (70S type) for protein synthesis and also houses cytoskeletal elements that help maintain shape and aid in cell division.
• Genetic material: It contains a single, circular DNA molecule( chromosome) in a dense, irregularly shaped region called nucleoid.
• Ribosomes: Small structures for protein synthesis.
• Capsule (optional):It surrounds some eubacterial cells, that are made up of polypeptides or polysaccharides. Capsule helps in causing disease in some bacteria, capsule protects bacteria from phagocytosis.
• Flagella: Long, whip-like structures used for locomotion.
• Pili (Fimbriae): Short, hair-like projections used for attachment and sometimes for DNA transfer during conjugation.

Classification of bacteria

Based on their shapes, bacteria is classified into four types:

• Coccus: These bacteria have spherical or nearly spherical shaped. Eg: Staphylococcus, Pneumococcus.
• Bacillus: These are rod-shaped bacteria.eg.  Lactobacillus
• Vibrio: These are comma-shaped bacteria. eg: V. cholera
• Spirillum: These are spiral-shaped bacteria. eg: Spirochaete

Based on gram’s stain, bacteria is classified into two types:

Gram- positive bacteria

• The cell wall of gram-positive bacteria is single layered and 150-200A0 thick and  consist of a high amount (about 80%) of peptidoglycan.
• The cell wall is very rigid due to high proportion of peptidoglycan.
• They retain blue or violet, or purple color in gram staining.
• The lipid content in gram-positive bacteria is low.
• Examples : Staphylococcus, Streptococcus, etc.

Gram-negative bacteria

• The cell wall is thin and contains a low amount (about 3-12%) of peptidoglycan.
• The Cell wall is elastic due to plastic nature of lipoprotein- polysaccharide mixture.
• They do not retain blue but retain pink color in gram staining.
• The amount of lipid content is high.
• Example: Salmonella, E.coli.

Reproduction in Eubacteria

• Eubacteria typically reproduce asexually through processes like binary fission and budding. During binary fission, the parent cell replicates its genetic material before dividing into two daughter cells.
• In unfavorable conditions such as a lack of nutrients, radiation exposure, chemical contamination, or extreme temperatures, certain bacteria form spores. These spores are highly resistant to heat, chemicals, toxins, and desiccation but are incapable of reproducing. Once conditions improve, the spores germinate and resume the reproductive cycle.
• Although eubacteria do not engage in true sexual reproduction, they can exchange genetic material through processes known as conjugation, transformation, and transduction.