FIGURE 5.

Acid stress mainly affected microbial riboflavin utilization and thereby MAIT cell activation. (A) The relative species abundances of SIHUMIx on day 1, day 5, and day 14 observed by metaproteomics was similar. (B) We stimulated MAIT cell with SIHUMIx communities on days 1, 5, and 14 cultivated in the bioreactor (BR) and (C) with mix communities based on the relative species abundances observed by metaproteomics. These were prepared from individual cultures on days 1, 5, and 14. (D) The unstressed bioreactor communities (BR) on day 1 and day 14 had a similar MAIT cell activating potential as their corresponding mix communities (mix), whereas on day 5 the BR community under acid stress significantly lost its MAIT cell activating potential (mean ± sd, n = 3, unpaired t-test). Quantitation of (E) riboflavin and (F) folate in the culture supernatant of SIHUMIx after bioreactor cultivation [ng/mL]. Bars represent mean ± sd, n = 3. Positive changes indicate vitamin secretion, negative values indicate vitamin uptake.