The same PET operon used in engineering of KO11 has also been used to construct a series of ethanologenic K12-derivatives, designated FBR for the Fermentation Biochemistry Research Unit. These strains were engineered with the goal of maximizing strain stability [43,44]. The most recent strain in this line, FBR5, produced ethanol from a variety of substrates at 86-92% of the theoretical yield [44]. Long-term stability of this strain was demonstrated by the maintenance of ethanol yields over 26 days of continuous culture on glucose or xylose [45]. However, the final ethanol concentration and yield from FBR5 in LB xylose are lower than LY168 in minimal medium (Table 2); additionally, these strains have the disadvantage of rich media dependence and contain plasmids.

2.4