Around the world, people have been drinking fermented tea for many hundreds of years, calling it by various names and praising its probiotic benefits as well as its refreshing flavor.
Many people are familiar with that leathery pancake called a SCOBY. That stands for Symbiotic Colony of Bacteria and Yeast. “Symbiotic” means that the bacteria and yeast strains live together in a complex, mutually supportive community, supporting and depending on each other.  The SCOBY is sometimes called the mushroom because it resembles the smooth, thick body of a mushroom.
The specific bacteria and yeast strains in the kombucha are what make it act the way it does, and what produce the fizz and flavor of kombucha. Not all kombucha cultures will contain the exact same strains, but these are some that have been recorded in studies:
- Acetobacter  is an aerobic (requiring oxygen) bacteria strain that produces acetic acid and gluconic acid. It is always found in kombucha. Acetobacter strains also build the scoby mushroom. Acetobacter xylinoides and acetobacter ketogenum are two strains that you might find in kombucha.
- Saccharomyces  includes a number of yeast strains that produce alcohol and are the most common types of yeast found in kombucha. They can be aerobic or anaerobic (requires an oxygen-free environment). They include Saccharomycodes ludwigii, Saccharomycodes apiculatus, Schizosaccharomyces pombe, Zygosaccharomyes, and Saccharomyces cerevisiae.
- Brettanomyces  is another type of yeast strain, either aerobic or anaerobic, that are commonly found in kombucha and produce alcohol or acetic acid.
- Lactobacillus : A type of aerobic bacteria that is sometimes, but not always, found in kombucha. It produces lactic acid and slime.
- Pediococcus : These anaerobic bacteria produce lactic acid and slime. They are sometimes, but not always, found in kombucha.
- Gluconacetobacter kombuchae  is an anaerobic bacteria that is unique to kombucha. It feeds on nitrogen that is found in tea and produces acetic acid and gluconic acid, as well as building the scoby.
- Zygosaccharomyces kombuchaensis  is a yeast strain that is unique to kombucha. It produces alcohol and carbonation as well as contributing to the mushroom body.
Kombucha also contains a variety of other nutrients, particularly various acids and esters that give the drink its characteristic tang and fizz. Included in these components is gluconic acid, which is the primary difference between the makeup of kombucha and the makeup of apple cider vinegar.
The actual bacteria, sugar, and acid content of kombucha depend on many factors, including the initial culture, the type of tea used, the type of sugar used, the strength of the tea, the type of water, the brewing time, the culturing temperature, and more. Due to the nature of kombucha, it is not possible to state an exact microbial composition for Kombucha. 
While different SCOBYs may vary in their exact makeup, what is common to all kombuchas is gluconic acid, acetic acid, and fructose. 
1. Ai Leng Teoha,, Gillian Heard, Julian Cox.(2044). Yeast ecology of Kombucha fermentation. International Journal of Food Microbiology, 95(2), 119-126. doi:10.1016/j.ijfoodmicro.2003.12.020
2. Jayabalan, R., Malini, K., Sathishkumar, M., Swaminathan, K., & Yun, S. E. (2010). Biochemical characteristics of tea fungus produced during kombucha fermentation. Food Science and Biotechnology, 19(3), 843-847.
3. Kurtzman, C. P., Robnett, C. J. and Basehoar-Powers, E. (2001), Zygosaccharomyces kombuchaensis, a new ascosporogenous yeast from ‘Kombucha tea’. FEMS Yeast Research, 1: 133–138. doi: 10.1111/j.1567-1364.2001.tb00024.x