Sunday, August 11, 2013
Pavilion (Sheraton San Diego)
Xylose is a 5 atoms sugar that is widely present in the hemicellulosic fraction of plant cell walls. Xylose is rarely present as soluble sugar in nature, and most of the fermenting microorganisms do not efficiently convert it to products. The previously homolactic engineered Escherichia coli strain CL3 (MG1655 ΔpflB ΔadhE ΔfrdA) showed a poor lactate productivity using xylose when compared to glucose. The slow growth of homolactic strains in xylose has been attributed to the low ATP yield in this carbon source. By deleting the ATP dependent xylose transport xylFGH and using adaptive evolution a new strain was isolated, which displayed high productivity of lactate in xylose mineral media. Genome sequence revealed several changes, including a point mutation in the gatC gene. The mutation is a change of a serine for a leucine in the 184 amino acid of the GatC protein. The mutation is located in the PTSIIC domain in a predicted transmembranal region. Previous analyses have indicated that Gat IIC proteins could have promiscuous functions and may act as secondary carriers. By knocking out the gatC gene and introducing the mutation in a non-evolved strain the participation of gatCS184L as a xylose transporter was confirmed. Its function as a xylose transporter was previously unknown. Quantitative proteomics revealed major changes in central metabolism as a result of the higher xylose consumption. The newly found transporter can be used to engineer strains for converting syrups from lingo-cellulosic feed-stocks into valuable chemicals such as D-Lactate, L-Lactate or ethanol.