Question

This is a Microbiology essay question. Please provide detailed answers.

There is no single gene that determines whether a bacterial cell is gram positive or negative.
a. Give examples of two genes that code for parts of the cell wall (gram positive, negative, or both).
b. Some phenotypes, like resistance to a particular antibiotic, are gained and lost by a bacterial lineage frequently. Why don’t we see bacterial lineages changing back and forth between gram positive and negative?

Answer 1

a.
The major component of the bacterial cell wall is peptidoglycan or murein. This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane.
genes that are responsible for peptidoglycan biosynthesis (Fig. 1): MurA, B, C, D, E, and F, and Pbp genes, two genes for d-Ala-d-Ala ligase (Ddl), and dd-carboxypeptidase (Dac)

b.
Certain specific phenotypes like resistance to a particular antibiotic are gained by the genes that are resent on the extra chromosomal circular DNA molecules, called plasmids. Bacteria may gain or lose these plasmids, accordingly, their respective phenotypes also.
Gram positiveness or gram negative ness comes out of the bacterial specific cell wall.
Gram negative bacteria contain thin or single layered peptidoglycan, whereas Gram positive bacteria contain thick or many layered peptidoglycan.
The genes, which are responsible for the peptidoglycan synthesis are located on the bacterial main chromosome but not on the plasmids. Unlike plasmids, these genes do not get lost or gained by the bacteria, so, bacteria don't change back and forth from Gram positive to Gram negative bacteria.