Fig. 2

Lactic acid production by Caldicellulosiruptor DIB 104C cultures generated during adaptive evolution. A Strain DIB 104C was applied in sequential repeated batch transfers using media containing microcrystalline cellulose as substrate and with or without externally added lactic acid as stress factor. The transfers in flasks without externally added lactic acid (referred to as “w/o LA”) and in fermenters with externally added lactic acid (referred to as “with LA”) were not continued (indicated by the symbol “x”) because the improvement in lactic acid production was lower as compared to the transfers in fermenters without externally added lactic acid. The numbers of sequential transfers in fermenters are shown in dotted line boxes. Occasionally during the repeated batch transfers, a significant increase in lactic acid production was observed (referred to as “steps”) and an aliquot of the respective cultures was stored for preservation and isolation of single-cell colonies (referred to as “SCC”). Culture names with an asterisk represent pure, isogenic strains; culture names without an asterisk represent mixed populations. B The mixed populations and isogenic strains with significantly improved lactic acid production (referred to as steps 1 to 7) were grown in fermenters on up to 200 g/l microcrystalline cellulose at 70 °C with pH stabilized at 6.4. Lactic acid production with cultures from evolution steps 1 to 7 are presented