Production of renewable chemicals for industrial, energy and consumer applications represents an important economic and societal challenge. Metabolic engineering is a promising route for producing chemicals by environmentally-friendly, sustainable fermentations using modified microbial biocatalysts. However, feedstock costs (usually refined sugar) drive which products can be economically produced by fermentation. Pectin-rich agricultural byproducts from fruit and vegetable processing represent plant biomass not currently utilized in fermentations, but are attractive due to their ease of hydrolysis to component monosaccharides and low current market value. Furthermore, these byproducts are produced consistently each year at high volumes, with over 10 million tons of citrus peel and 70 million tons of sugar beet pulp produced worldwide from the citrus juice and sugar industries, respectively. This thesis describes the use of D-galacturonic acid (D-galUA) present in these byproducts for microbial fermentations and renewable chemical production. The identification of a novel eukaryotic D-galUA transporter, GAT-1, from N. crassa is described. GAT-1 and related transporter from A. niger, GatA, demonstrate utility in S. cerevisiae for bioconversions to L-galactonate and meso-galactarate. Importantly, GatA allows for co-consumption of D-galUA and D-glucose in S. cerevisiae, which are present in high concentration in pectin-rich hydrolysates. We additionally characterize the D-galUA catabolic elements of the basidiomycete yeast, R. toruloidies, a highly efficient D-galUA utilizing organism and potential host for D-galUA bioconversions. Lastly, the commercial potential for meso-galactaric acid fermentations by S. cerevisiae is discussed.