Cytoplasmic Granules in Bacteria

Last updated on June 17th, 2021

Concentrated deposits of certain substances which are presented/located in the cytoplasm of certain bacteria are known as cytoplasmic granules or inclusion bodies. They serve as storage areas for nutrients, e.g. volutin granules are reserves of high energy stored in the form of polymerized metaphosphate.

The number and nature of the inclusions vary depending on the bacterial species and the nutritional state of the organism’s environment. Common types of granules that are microscopically visible in certain bacteria stained with specific dyes are:

Metachromatic granules of Corynebacterium spp
Metachromatic granules of Corynebacterium spp
  • Polysaccharide granules (glycogen): a storage form of glucose and
  • polyphosphate granules: a storage form for inorganic phosphates (volutin granules, also known as metachromatic granules, are composed of polyphosphate)
  • poly-β-hydroxybutyrate (PHB) granules: a reserve carbon and energy source.
  • Elemental sulfur: Intracellular globules of elemental sulfur may be seen accumulated in certain bacteria growing in environments rich in hydrogen sulfide.

Cytoplasmic granules/inclusion bodies stain characteristically with certain dyes;

  1. Volutin granules appear as “metachromatic” granules, stains intense reddish-purple color with methylene blue dye (instead of blue, as one would expect), and can be observed by light microscopy.
  2. Poly-β-hydroxybutyrate (PHB) granules can be stained with lipid-soluble dyes such as Nile blue.
  3. Glycogen can be stained brown with iodine.

Metachromatic granules are characteristics of Corynebacterium diphtheriae

About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

1 Comment

  1. Hi, i am basically working on bacterial diversity in cold environments specially Himalayan glaciers.
    My question is that if there is any major changes in cytoplasmic granules composition of cold adapted bacteria and direct relation with their metabolic enzymes such as lipase?

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