Production of extracellular indole in P. alvei. Cell growth and extracellular indole accumulation in LB (A) and extracellular indole accumulation in LB supplemented with different carbon sources (B) at 37°C at 250 rpm. Cell growth (closed circle) was determined via the optical density at 600 nm (OD600). Glucose (Glu), glycerol (Gly), and lactose (Lac) in 0.5% (w/v) were added at the beginning of the culture and cells were cultured for 36 h and indole production was measured. Experiments were performed in triplicate and one standard deviation is shown.