Fig. 1

Phylogenetic tree of the AdhA proteins and ethanol yield for 11 C. thermocellum strains expressing adhA genes from different organisms. a The distance-based phylogenetic tree generated from the alignments of the AdhA proteins. b Ethanol yield for all of the adhA-expressing strains. Strains were cultured in MTC-5 medium containing 4.7 g/l cellobiose and 6 μg/ml thiamphenicol at 55 °C for 72 h. The maximum theoretical yield is 4 mol of ethanol per mole of cellobiose consumed. Data were collected from triplicate experiments. Error bars represent one standard deviation. Wild-type C. thermocellum expressing the empty vector pDGO144 (LL1535) was used as negative control (indicated in red), and the strain expressing T. saccharolyticum adhA was used as positive control (indicated in green). All of the other 10 strains were shown as the experimental group (indicated in gray). Ethanol yields of experimental group strains were compared to the positive control using a two-tailed unpaired t test, and p values are reported where significant