Project description:Glycerol is an attractive feedstock for biofuels since it accumulates as a byproduct during biodiesel operations; hence, it is interesting to consider converting glycerol to hydrogen using the formate hydrogen lyase system of Escherichia coli which converts pyruvate to hydrogen. Starting with Escherichia coli BW25113 frdC that lacks fumarate reductase to eliminate the negative effect of accumulated hydrogen on glycerol fermentation and by using both adaptive evolution and chemical mutagenesis combined with a selection method based on increased growth on glycerol, we obtained an improved strain, HW2, that produces 20-fold more hydrogen in glycerol medium (0.68 mmol/L/h) compared to that of frdC mutant. HW2 also grows 5-fold faster (0.25 1/h) than BW25113 frdC on glycerol, so it achieves a reasonable growth rate. Corroborating the increase in hydrogen production, glycerol dehydrogenase activity in HW2 increased 4-fold compared to BW25113 frdC. In addition, a whole-transcriptome study revealed that several pathways that would decrease hydrogen yields were repressed in HW2 (fbp, focA, and gatYZ) while a beneficial pathway, eno which encodes enolase was induced.
Project description:The goal of the study is to use Next generation sequencing (RNA-seq) and 13C based flux analysis to study the underlying regulation of citric acid metabolism in mixed culture fermentation (glucose and glycerl) of Yarrowia lipolytica. We sequenced the RNA from 4 different samples in the mixed culture (glucose and glycerol) under oxygen excess and limited conditions with 2 replicates each . Transcriptional profiles showed that under oxygen limited conditions, due to deficient mitochondrial activity, citric acid is being consumed back after glycerol exhaustion eventhough glucose is present in excess. Transcriptome and fluxome profiles showed that glucose is mainly directed towards the Pentose phosphate pathway in the dual substrate fermentations.
Project description:The goal of the study is to use Next generation sequencing (RNA-seq) to study the underlying regulation of glycerol metabolism in mixed culture fermentation (glucose and glycerol) of Rhodosporidium toruloides. We sequenced the RNA from 4 different samples in the mixed culture (glucose and glycerol) with 2 replicates each. Transcriptional profiles showed that glycerol might be produced intracellularly and glycerol kinase (GUT1) and glycerol 3–phosphate dehydrogenase (GUT2) enzymes were not down-regulated in the presence of glucose at the transcriptional level. It also showed that this yeast has a different regulation compared to S.cerevisiae. Certain insights into lipid biosynthesis on these mixed cultures are provided at systems level. This analysis provides interesting targets for metabolic engineering in this organism growing on glucose and glycerol.