All sourdough starters out there are made up by different yeast cultures. This means that it is very hard to say with certainty which yeast or bacteria that lives in your sourdough starter. There are several things that will contribute to this. First the ingredient the water and the flour that is used, but also the place where the starter started and by whom.The combination of the bacteria from the kitchen, the water, the flour makes every starter unique.
Having said that, the microorganisms in sourdough starters do contain a combination of both wild yeast and lactic acid bacteria.These two “eats” or ferment the sugar in the flour that results in bubbles and its the bubbles that makes your dough rise to a bigger size.
What happens next is that the bacteria break down the left over products from the fermentation process which produces lactic and acetic acid and these two are what gives the characteristic sour flavour of sourdough bread.
They also lower the pH of the bread which works as a preservative, and that prevents the bread from going bad as fast as bread made without it
Both yeast and bacteria live in sourdough starters and are needed and normal. The yeast and bacteria are the good guys and we need them to make our delicious sourdough bread!