The cultures can vary. There is always a range of different bacteria and yeasts.
The following bacteria are commonly included:
Acetobacter xylinum, Acetobacter pasteurianus, Acetobacter aceti, Acetobacter nitrogenifigens sp. nov., Gluconobacter oxydans, Gluconacetobacter A4 (G. sp. A4), Gluconacetobacter kombuchae nov..
Of the yeasts, the following species are usually included: Saccharomyces/mycoides, Zygosaccharomyces, Brettanomyces, Candida...and a lot more :)