What properties allow for bacteria to survive inside of the stomach?Are gastrointestinal bacteria tolerant to low PH or do they posses other qualities that allow for them to tolerate stomach acids?

Question 1:

What properties allow for bacteria to survive inside of the stomach?

Are gastrointestinal bacteria tolerant to low PH or do they posses other qualities that allow for them to tolerate stomach acids?

Are there any coupled reactions that are useful to make products that we use for technology?