What about the hydolases ? How do they work and where do they come from ? Why do we use hydrolases ?

These enzymes have features that make them attractive as reporters. They are known to be relatively stable, exhibit activity under different conditions (e.g. pH and temperature), and various colorimetric and fluorescent substrates are available (Kiernan, 2007).

LacZ : beta-galactosidase

PhoA : Alkaline phosphatase

Aes : Carboxyl esterase

Nagz : Glycoside hydrolase

GusA : beta-glucuronidase

The E. coli β-glucuronidase is a tetrameric enzyme that hydrolyzes a wide variety of β-glucuronides.