Recipes for spontaneous (wild) ginger ale sometimes refer to the starter as the "ginger bug". What is the ginger bug? Is it just an ordinary lactobacillus; is it a type of yeast? Is it something that is all around us, or something that is found specifically on the ginger? What role does the ginger play: is it simply a flavouring agent, does it act as a preservative, or is it something special (for instance, a carrier of important microörganisms that aren't found anywhere else)?
(When I say "ginger ale", I mean a fermented soft-drink that uses a small amount of sugar as the fermentable base. I'm not talking about beer that is flavoured with ginger.)