Figure 1
The bioethanol-producing yeast strain Ethanol Red cross-feeds Lactobacillus fermentum. (A) Schematic representation of the co-culture system. The yeast cell suspension is placed in the well and the insert prefilled with the L. fermentum cell suspension is placed on top of it. The arrows represent solute diffusion across the membrane separating the two cultures. (B) The density of yeast cells in cultures of the wild-type laboratory strain 23344c or the industrial strain Ethanol Red (E⋅RED) were monitored by counting colony-forming units (CFUs) just after inoculation (0 h) and after 48 h of co-culture. (C) L. fermentum cell density was monitored by counting CFUs in co-cultures with the 23344c wild-type or the Ethanol Red (E⋅RED) yeast strain, just after inoculation (0 h) and after 48 h of co-culture. In a control experiment, L. fermentum cell density was assessed after cultivation, in the absence of yeast, in the presence or absence of all 20 amino acids. (D) The values presented in (B and C) were used to calculate the cell propagation ratio of L. fermentum co-cultivated with 23344c or E⋅RED. Bars represent averages of minimum three independent experiments ± standard deviation (SD). * indicates a statistically significant difference as determined with the unpaired t test. * P < 0.034; *** P < 0.0002; **** P < 0.0001.
