Expression levels of genes regulated by Fur. The log10-transformed expression levels of Fur regulon genes which were successfully quantified (57 genes in total) in strain P (0% or 5% ethanol) and in tolerant strains A-F (5%) are presented. The expression levels were sorted in the decreasing order of the expression levels in strain P without ethanol stress. Black dot lines represent the expression levels in strain P without ethanol stress for the reference. A list of Fur regulon member genes in the same order is presented in Additional file 4.