Saran's Learn Microbiology

  ARCHAEA ·        Prokaryotic in nature. ·     The word Archaea is derived from the Greek word Archaios , meaning “Ancient” or “Primitive,” and indeed some archaea exhibit characteristics worthy of that name. ·        In 1977, Carl Woese and George Fox recognized that the Archaea have a separate line of evolutionary descent from bacteria in phylogenetic tree based on the sequencing of 16S Ribosomal RNA (rRNA), and divided prokaryotes into two evolutionary domains (Bacteria & Archaea), as part of the Three - domain system. ·        Unicellular in nature. ·        Measured in micrometer (µm) and Size was ranged from 0.1 µm to 15 µm. ·     Shape range - Spherical, rod-like, spiral, plates, irregularly shaped, lobed, needle-like filamentous, rectangular rods and flat square shape. ·     Cell wall is made up of Polymers other than Peptidoglycan. Because of this reason, Archaea was differentiated from Bacteria by Carl Woese and George Fox. Therefore, the absence or presenc

  GLYCOCALYX ·     Some bacterial cells have a gelatinous, sticky substance that surrounds the outside of the cell. This substance is known as a Glycocalyx (Plural: Glycocalyces), which literally means “Sweet cup” or “Sugar coat”. ·    Glycocalyx may be composed of Polysaccharides or Polypeptides, or both Polysaccharides and Polypeptides. Its chemical composition varies widely with the species. These chemicals are produced inside the cell and are extruded onto the cell’s surface. ·      When the Glycocalyx of a bacterium is composed of organized repeating units of organic chemicals firmly (strongly) attached to the cell’s surface, the Glycocalyx is called a Capsule. In contrast, a loose, water-soluble Glycocalyx is called a Slime layer. ·    Glycocalyx is the currently accepted term used to refer to all Polysaccharide-containing substances found external to the cell wall, from the thickest Capsules to the thinnest Slime layers. ·        Capsules is not present in all bacteria

  PILI ·        Pili are long hair like tubular microfibers like structure. ·        Pili are present on some Gram negative bacteria only. ·        Based on Hemagglutinating ability and Mannose sensitivity, Pili are classified into four types. They are i.        Type I - Occur in Escherichia coli, Klebsiella, Shigella and Salmonella . They are mannose sensitive. ii.      Type II - Present in Salmonella gallinarum and Salmonella pullorum,  devoid of any hemagglutinating or adhesive properties. iii.    Type III - Present in some strains of Klebsiella, Serratia , etc. They agglutinate RBC only after heating and are mannose resistant. iv.    Type IV - Mannose resistant and occur in Proteus . ·        Pili are made up of protein called Pilin. ·        Comparatively, Pili are longer than Fimbriae and shorter than Flagella. ·        Approximate length of Pili is 0.5 µm – 2.0 µm. ·        Number of Pili per cell is very less. It is usually 1 to 10 per cell. They ar