Question

What are the differences in cell envelope structure between gram-negative and gram-positive bacteria? How might these differences become important if you wish to genetically engineer bacteria to excrete proteins into the extracellular fluid?

Answer 1

The main difference in cell envelope structure between gram positive and gram negative bacteria is-

• cell wall of gram positive bacteria is thick ( 20-30 nm) in comparison to gram negative bacteria which is very thin (8-12 nm).
• gram-positive bacteria contains thick peptidoglycan layer, whereas the peptidoglycan layer is very thin in gram.negative bacteria.
• cell wall of gram negative bacteria contains an outer wall which is absent in gram positive bacteria.
• gram negative bacteria contains high amount of lipopolysaccharide ( LPS) in relation to gram.positive bacteria.

when compared for the production of recombinant protein, if gram negative bacteria is used, which contains an outer layer containing lipopolysaccharides that can interfere with the protein secretion into the extracelular medium. Thus resulting in accumulation of secreted protein in periplasm in the form of inclusion bodies. These protein forms are inactive and may remain difficult to recover them back in the active form.

Whereas, in gram-positive bacteria, as they do not have an additional outer layer, the secreted recombinant protein can be released directly into culture medium which makes them more suitable for genetic engeenering.