Bacteria are a large group of microscopic, unicellular organisms and have been grouped into prokaryotic, which means the absence of the nucleus and they have a simple internal structure, including capsule, cell wall, DNA, Flagellum, Pilli, Cytoplasm, and Ribosomes. They exist in every place around us and are present in communities of millions. In length, the complete bacteria measure only a few micrometers.
A bacterium is a singular word for bacteria. The study of bacteria is known as bacteriology and it’s a branch of microbiology.
Types Of Bacteria
There are several different types of bacteria and are mainly classified by their:
- Shapes: coccus, Bacillus, Vibrio, spirillum or spirochete.
- Cell wall composition: Gram-positive and Gram-negative.
- Nutritional Patterns: Autotrophic or heterotrophic.
- Mode of Respiration: Aerobic or Anaerobic.
Here, let us explore more information about the difference between Gram-positive and Gram-negative bacteria.
Difference between Gram-positive and Gram-negative Bacteria
|Gram-positive bacteria||Gram-negative bacteria|
|Cell Wall||Their cell wall is smooth and single layered||They have a wavy and double layered cell-wall|
|Cell Wall thickness||The thickness of the cell wall is 20 to 80 nanometres||The thickness of the cell wall is 8 to 10 nanometres|
|Peptidoglycan Layer||It is a thick layer||It is a thin layer|
|Teichoic acids||Presence of teichoic acids||Absence of teichoic acids|
|Outer membrane||The outer membrane is absent||The outer membrane is present|
|Porins||Absent||Occurs in Outer Membrane|
|Mesosome||It is more prominent.||It is less prominent.|
|Morphology||Cocci or spore-forming rods||Non-spore forming rods.|
|Flagella Structure||2 rings in basal body||4 rings in basal body|
|Lipid content||Very low||20 to 30%|
|Toxin Produced||Exotoxins||Endotoxins or Exotoxins|
|Resistance to Antibiotic||More susceptible||More resistant|
|Examples-||Staphylococcus, Streptococcus, etc.||Escherichia, Salmonella, etc.|
|Gram staining characteristics||
These bacteria retain the crystal violet color even after they are washed with acetone or alcohol and appear as purple colored when examined under the microscope after gram staining.
These bacteria do not retain the stain color even after they are washed with acetone or alcohol and appear as pink colored when examined under the microscope after gram staining.
Gram-positive And Gram-negative Bacteria
Gram-positive and gram-negative bacteria are categorized on the basis of the ability to hold the gram stain. The gram-negative bacteria are stained by a counterstain such as safranin and they are destained because of the alcohol wash. Hence under a microscope, they are noticeably pink in color. Gram-positive bacteria, on the other hand, retains the gram stain and show a visible violet color upon the application of mordant(iodine) and ethanol(alcohol).
Gram-positive bacteria have a cell wall composed of multiple layers of peptidoglycan that forms a rigid and thick structure. Its cell wall additionally has teichoic acids and phosphate. The teichoic acids present in the gram-positive bacteria are of two types – the lipoteichoic acid and the teichoic wall acid. The cell wall is known as murein.
In gram-negative bacteria, the cell wall is made up of an outer membrane and several layers of peptidoglycan. The outer membrane is composed of lipoproteins, phospholipids, and LPS. The peptidoglycan stays intact to lipoproteins of the outer membrane that is located in the fluid-like periplasm between the plasma membrane and the outer membrane. The periplasm is contained with proteins and degrading enzymes which assist in transporting molecules. The cell walls of the gram-negative bacteria unlike the gram-positive lacks the teichoic acid. Due to the presence of porins, the outer membrane is permeable to nutrition, water, food, iron, etc.
Gram Stain Test
Gram stain or Gram’s method is a method of staining that is used to discriminate and for the classification of bacterial species into two broad groups – the Gram-positive and Gram-negative. This process distinguishes bacteria on the basis of physical and chemical properties of their cell walls through the identification of peptidoglycan that is found in the cell wall of the gram-positive bacteria. A very small layer of peptidoglycan is dissolved in gram-negative bacteria when alcohol is added.
For more information on various topics like Bacteria and Bacterial Diseases, visit BYJU’S.