Alfredo Martinez: Fuel ethanol production from corn stover with ethanologenic bacteria
Starting the afternoon, Alfredo Martinez from the Institute of Biotechnology at UNAM in Mexico (Department of Cellular Engineering and Biocatalysis) spoke about Fuel ethanol production from corn stover with ethanologenic bacteria.
Regarding the challenge of biofuels Mr Martinez first showed how to generate ethanol (agro-fuels) and (agro-) chemicals from lignocellulose with the use of ethanologenic bacteria. The main objective of these projects is to design microorganisms and processes to transform all sugars contained in lignocellulose (cellulose and hemicellulose: pentoses, hexoses, and disaccharides) into ethanol or other biochemicals, mainly organic acids.
Then Mr Martinez showed ways to generate fermentable sugars from hemicellulose (thermochemical hydrolysis using diluted acid hydrolysis at more than 100 ° Celsius) and cellulose (enzymatical hydrolysis at pH 4.5-5 at 50 ° Celsius).
Two main strategies to convert pentoses into ethanol were shown: a microorganism that already produces ethanol like yeast (extending the range of metabolizable sugars, such as xylose) and microorganism that are not efficient producing ethanol, but consume a wide range of sugars, including xylose and xylose (complementing the pathways to produce ethanol and eliminating the formation of other fermentation products, i.e. in Escherichia coli). The theoretical yield from this pathway is 0.64 liters of ethanol per kg of sugar.
Mr Martinez then showed specialized ethanologenic E. coli strains that has been continuously developed and improved, using metabolic engineering, to produce ethanol from a wide array of sugars and conditions.
The new generations of ethanologenic E. coli, produces ethanol as the sole fermentation metabolite, and yields above 90% of the theoretical can be obtained from pentose or hexose sugars.
Mr Martinez continued his presentation with examples using sugars obtained from the sequential thermochemical hydrolysis and enzymatic saccharification of corn stover. He shows that all sugars (pentoses and hexoses) were fermented to ethanol with the ethanologenic E. coli strain called MS04 within 36 hours. Based on these results, in Mexico, in the Bajio region, 825 million liters of ethanol can be produced from corn stover, and in the Tequila region, 72 million liters of ethanol from blue agave bagasse residues.
At the end of the presentation Mr Martinez explained new developments with ethanologenic E. coli derivative strains having the ability to secrete β-glucosidases to produce ethanol from cellobiose.