Microorganisms in ginger root

If you put some ginger is water with sugar it will start fermenting. What are microorganisms in the ginger, probably several yeasts, but are there some bacterias or other things that might consume sugar or the alcohol produced by the yeast?

it's hard to say what would be there. There are literally thousands of microorganisms (bacteria, fungi including yeast, and protists) in a gram of soil. In addition, the root will have been exposed to numerous others between the time it was harvested and you got it. Most of these will be washed off when you clean the root, but not all. I would not count on getting a reliable fermentation from the native flora on the root. Pasteurize your extract and add back a quality yeast strain that fits your goals.