Question #4: Now expanding on the thought process that the more cellular layers
ID: 191138 • Letter: Q
Question
Question #4: Now expanding on the thought process that the more cellular layers involved, the less likely the Gram stain will stain negative...you are now focused on the External Layer (EL) of P, uncinatum. Turns out that the EL is the junctional pore location of electron-dense "slime" extrusion, as well as the location of fibril attachment (both the slime and active fibril activity allow for "gliding" locomotion). on-motile stains of P. uncinatum have locations for fibrils along the EL, but empty pore channels (meaning no "slime" production). This is contrasted with highly motile, gliding stains that have BOTH the production of "slim" as well as active fibrils. Which is more likely to stain gram-negative, a motile or non-motile strain? Why?
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
The motile strain is more likely to stain gram neagtive as the continous slime production and the active fibrils restrict the movement of the dye to the peptidoglycan layer. The non-motile strains have empty strains,i.e, no slime production which makes it easier for the stain to travels through the pores and stain the peptidoglycan layer making it stain like a gram positive organism.