LY168 produced 0.5 g ethanol per gram of xylose during growth in min­eral salts medium with betaine, a value close to the theoretical maximum of

LB yeast extract + tryptone

Min minerals + 1 mM betaine

YE yeast extract supplemented with phosphate

YEP supplemented with yeast extract and peptone

Synth minerals supplemented with a mixture of vitamins

5 G 8 g of glucose added per liter

a Yomano et al. 2007

0.51 (Yomano et al., submitted). As described in detail below, osmolyte stress in mineral salts media limits biocatalyst performance and betaine supple­mentation combats this stress [42]. The amount of ethanol produced by LY168 during 24-h fermentations in mineral salts medium with betaine or LB were equivalent. Thus, strain LY168 fulfills the goal of constructing a microbial biocatalyst that produces ethanol without dependence on costly nutritional supplements. As presented in Table 2, the LY168 ethanol yield from xylose is higher than any previously reported ethanologenic biocatalyst.

2.3