Question #3: What color would the E. coli cell be following a Gram stain? Explai
ID: 191136 • Letter: Q
Question
Question #3: What color would the E. coli cell be following a Gram stain? Explain why with a clear explanation of the Gram staining process and pertinent cellular components that cause cells to stain a particular color. On the other hand, what color should Cyanobacteria stain (you were given the answer above, don't mess this up)? Explain why, once again drawing from your knowledge of how the Gram staining procedure works to accurately stain cells, might it be challenging to accurately stain Cyanobacteria.
Based on the presence of peptidoglycan, Cyanobacteria are considered prokaryotes. But, due to the likely endosymbiotic relationship that has evolved with algae and plants they also possess chloroplast. Cyanobacteria are very difficult to classify as gram positive or gram negative. This is normally due to the fact that although there is an overall gram negative structure, the peptidoglycan is thicker in Cyanobacteria than what is typically seen in gram negati bacteria. Additionally, it has been found that there is an increase in the peptidoglycan chain cross-linking of Cyanobacteria (Hoiczyk et al. 2000). ve Below is an electron microscopy comparison of the gram-negative cell envelopes of (A) cyanobacterium (Phormidium uncinatum) and (B) Escherichia coli Mp (Hoiczyk E, Hansel A J. Bacteriol. 2000;182:1191-1199) he above comparison, EL represents a serrated External Layer, characteristic of the specific type of Cyanobacteria pictured. OM represents the Outer Membrane, P is the Peptidoglycan layer, and CM is the Cytoplasmic Membrane. You not concerned with the EL for staining purposes; focus on the three primary structures that help distinguish a gram from a gram negative cell n order to answer why Cyanobacteria (A), given the characteristics as shown above, are make the cell challenging to gram stain correctly as GRAM NEGAT VE.Explanation / Answer
1.What color would the E. coli cell be following a Gram stain?
The E. coli cell would appear pink following a Gram stain.
2. Explain why with a clear explanation of the Gram staining process and pertinent cellular components that cause cells to stain a particular color.
Gram staining procedure:
When the bacteria is stained with primary stain Crystal Violet and fixed by the mordant, some of the bacteria are able to retain the primary stain and some are decolorized by alcohol. The cell walls of gram positive bacteria have a thick layer of protein-sugar complexes called peptidoglycan and lipid content is low. Decolorizing the cell causes this thick cell wall to dehydrate and shrink, which closes the pores in the cell wall and prevents the stain from exiting the cell. So the ethanol cannot remove the Crystal Violet-Iodine complex that is bound to the thick layer of peptidoglycan of gram positive bacteria and appears blue or purple in colour.
In case of gram negative bacteria, cell wall also takes up the CV-Iodine complex but due to the thin layer of peptidoglycan and thick outer layer which is formed of lipids, CV-Iodine complex gets washed off. When they are exposed to alcohol, decolorizer dissolves the lipids in the cell walls, which allows the crystal violet-iodine complex to leach out of the cells. Then when again stained with safranin, they take the stain and appears pink in color.
3. On the other hand, what color should Cyanobacteria stain (you were given the answer above, don't mess this up)? Explain why, once again drawing from your knowledge of how the Gram staining procedure works to accurately stain cells, might it be challenging to accurately stain Cyanobacteria.
Being Gram-negative bacteria, E. coli have an additional outer membrane that is composed of phospholipids and lipopolysaccharides. The presence lipopolysaccharides on the outer membrane of bacteria gives it an overall negative charge to the cell wall. Because of these properties, E. coli does not retain crystal violet during the Gram staining process.