Figure 5.

Histamine can be produced by L. reuteri from L-histidine delivered via DM. Stationary phase WT L. reuteri was incubated for 2 h in either saline with and without 3% maltose or 2% glycerol, or 4 mg/ml L-histidine with and without 3% maltose or 2% glycerol. Histamine production was increased with addition of 3% maltose to 4 mg/ml L-histidine solution (white bar black border) compared to just 4 mg/ml L-histidine (black bar and gray bar black border). When L-histidine at 4 mg/ml was provided via DM the overall levels of histamine produced were significantly lower (middle 3 bars) compared to L-histidine provided in solution (left 4 bars), likely due to less immediate availability of L-histidine to the bacteria. However, when the concentration of L-histidine loaded into DM was increased to 30 mg/ml, significantly more histamine was produced (right 3 bars) despite any caveats related to slower access to L-histidine due to availability only via diffusion out of DM. Error bars represent standard error of the mean. Statistical significance is indicated by the following: ^*P < 0.05, ^**P < 0.01.