A High-Fiber Diet

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Science  13 Apr 2007:
Vol. 316, Issue 5822, pp. 175
DOI: 10.1126/science.316.5822.175b

In the race to replace fossil fuels with biofuels, microbial fermentation may become a key technology. However, microbes can do only so much and balk when their food contains too much lignin. This is not uncommon because the fibrous tangle of lignin and cellulose, called lignocellulose but better known as wood, is ubiquitous. To add to the problem, the enzymatic breakdown of cellulose is not as rapid as the enzymatic breakdown of starches. Jeffries et al. present the genome sequence of the yeast Pichia stipitis Pignal, which can digest lignocellulose and can transform xylose, a component of lignocellulose, into ethanol. The yeast sequenced was isolated from insect larvae and is related to yeasts found in the gut of beetles that frequent rotting wood. The 15.4-Mb genome is divided into eight chromosomes and includes 5841 predicted genes, including a group of cellulases and xylanases and a number of genes encoding putative xylose transporters. Further analysis showed which genes in which metabolic pathways respond to changes in xylose, glucose, or oxygen. Unlike Saccharomyces cerevisiae, which regulates fermentation according to glucose availability, P. stipitis regulates fermentation according to oxygen levels, which is reflected in how the genes respond to oxygen. — PJH

Nat. Biotechnol. 25, 319 (2007).

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