ased on the presence of peptidoglycan, Cyanobacteria are considered prokaryotes.

Question

ased on the presence of peptidoglycan, Cyanobacteria are considered prokaryotes. But, due to the likely ndosymbiotic 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 overal gram negative structure, the peptidoglycan is thicker in Cyanobacteria than what is typically seen in gram ne bacteria. Additionally, it has been found that there is an increase in the peptidoglycan chain cross-linking of Cyanobacteria (Hoiczyk et al. 2000). Below is an electron microscopy comparison of the gram-negative cell envelopes of (A) cyanobacterium (Phormidium uncinatum) and (B) Escherichia col. CM (Hoiczyk E, Hansel A J. Bacteriol. 2000;182:1191-1199) In the above comparison, EL represents a serrated External Layer, characteristic of the specific type of Cyanobacteria d. OM represents the Outer Membrane, P is the Peptidoglycan layer, and CM is the Cytoplasmic Membrane. You picture are not concerned with the EL for staining purposes; focus on the three primary structures that help distinguish a gram tive from a gram negative cell in order to answer why Cyanobacteria (A), given the characteristics as shown above, posi make the cell challenging to gram stain correctly as GRAM NEGATIVE. What structurels) in the cyanobacteria cell, (A) pictured above, make the cell gram negative? What characteristics might make the cell appear gram positive following staining? (2 points) outer membran Pepidoglycan Ct Generally, how does the peptidoglycan differ between a Gram negative and Gram positive cell? In the specific case of Cyanobacteria, what effect might the 'increase in peptidoglycan chain cross-linking have on the 1. 2. oföram staining? (4 points) CV (If you have thick pep loyer wnat will get dthaEeoli cell he following a Gram stain? Explain why with a clear explanation of the Gram

Explanation / Answer

1. The thick EL(external layer) makes it gram negative.Thick, multi layered peptidoglycan layer would make it gram positive.

2.Thin, single layered peptidoglycan layer in gram negative and thick multi layered peptidoglycan layer in gram positive. In his test, if peptidoglycan layer becomes more cross linked, bacteria will retain the crystal violet dye because of a thick layer of peptidoglycan and thus become gram positive. In contrast, Gram negative bacteria do not retain the violet dye and are colored red or pink. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall.

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