When observing two different prokaryotic organisms that are both stained using the same staining procedure...?

Question

...,what characteristics of the cells can allow someone to identify them as different species?

Answer 1

You can differentiate in part by morphology.  You determine if the cells are bacilli (rods), cocci (spheres) or spirilla.  This will differentiate to a small degree (different shapes must be different species).  However, many different species share the same basic morphology.

Answer 2

In the most common and useful staining method:  gram staining, the organisms can almost universally classified into two groups.  Gram + organisms stain purple and have thicker cell walls than the pink gram - orgs with thinner cell walls.  This staining method does distinguish that two orgs are different species given their gram natures are different, it does not determine what species the org actually is.  Other things to consider in concert with the gram nature of the organism is its morphology (shape), size (both on a plate and under the microscope, edge features, color, optical quality, and smell.  The most accurate way to determine prokaryotic species is to subject them to a battery of biochemical tests.  Gram nature is also relevant here because you would only do certain biochemical tests on G- and a different set on G+.

There are plenty of other staining methods that select for certain characteristics.  I would check a microbiology text or lab text if you want a deeper understanding.

Answer 3

You can also observe whether any of them contain spores. If so, you'll know that they are either Bacillus or Clostridium. (In a simple or Gram stain, they'll show up just as colorless circles in the middle of the cell.  In a spore stain, they will clearly show up as your primary dye).