1. The Natural Habitat Of Microbes

Microbial cells in nature live as:  

2. Laboratory Studies Of Microbes

Knowledge on microbial structures, physiology, biochemistry and genetics can be better understood from homogenous populations rather than form mixed populations. Homogenous populations can be obtained in the laboratory by using microbiological procedures. A. Microscopes and Microscopy Techniques Bright Field Microscope: Staining: Dyes are organic compounds that have affinity for specific cellular material and increase contrast.
    Cationic Dyes (positively charged): Cell walls are negatively charged and hence positively charged chromophores (chroma = color) can bind (methylene blue, crystal violet, safrarnin). Dyes can be simple (cationic or anionic) or differential types. A smear is prepared air dried, heat fixed and flooded with the dye for a minute, washed, blotted, dried and observed using an oil immersion lens.

    Anionic Dyes (negatively charged): Negative staining with India Ink or Nigrosine. Negatively charged dyes are repelled by the negative charges on the cell wall of bacteria and hence the background is colored but not the cell. Used to demonstrate capsulated microbes.

    Differential Dyes: Gram staining (the thick cell walls of Gram-positive bacteria do not allow the alcohol to penetrate into the cell and hence are not destained whereas the thin Gram-negative cells are), flagella staining and spore staining are examples of this.

Phase Contrast Microscope:

Fluorescence Microscope:

Electron Microscope:

Transmission Electron Microscope (TEM):
Cells are too thick to be seen thro' a TEM and thin sections are prepared (using an ultramicrotome) following a special protocol (cells are dehydratedfixed The sections are stained with heavy metals such as Osmium tetraoxide, Uranyl acetate or phosphotungstic acid which scatter electrons.

Scanning Electron Micoscope (SEM):
External rather than internal structures are observed by a Scanning Electron Microscope (SEM). Gold is used as a stain for scattering electrons.

B. Culturing Microbes

Author and HTML'd by: Dr Bharat Patel <>

[Created 20 Sept 1995]
[Modified 2 Aug 1997]