Gram-positive Bacteria - Characteristics

Characteristics

The following characteristics are generally present in a Gram-positive bacterium:

1. cytoplasmic lipid membrane
2. thick peptidoglycan layer
   • teichoic acids and lipoids are present, forming lipoteichoic acids, which serve to act as chelating agents, and also for certain types of adherence.
3. capsule polysaccharides (only in some species)
4. flagellum (only in some species)
   • if present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer.
5. The individual peptidoglycan molecules are cross-linked by pentaglycine chains by a DD-transpeptidase enzyme. In gram-negative bacteria, the transpeptidase creates a covalent bond directly between peptidoglycan molecules, with no intervening bridge.

Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer. In Gram-negative bacteria, the S-layer is attached directly to the outer membrane. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acids in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.