Tolerance assay of lignocellulose pretreatment’s toxins. Toxin tolerance assays were conducted with different concentrations of (a.) furfural, (b.) hydroxymethylfurfural, and (c.) nickel. The OD600 values of engineered E. coli strains cultured in PYG medium were also measured. The relative growth rates were compared with the strain controls cultured in PYG medium without toxins.