title: Short communication: Conversion of lactose and whey into lactic acid by engineered yeast.
abstract: Lactose is often considered an unwanted and wasted byproduct, particularly lactose trapped in acid whey from yogurt production. But using specialized microbial fermentation, the surplus wasted acid whey could be converted into value-added chemicals. The baker's yeast Saccharomyces cerevisiae, which is commonly used for industrial fermentation, cannot natively ferment lactose. The present study describes how an engineered S. cerevisiae yeast was constructed to produce lactic acid from purified lactose, whey, or dairy milk. Lactic acid is an excellent proof-of-concept chemical to produce from lactose, because lactic acid has many food, pharmaceutical, and industrial uses, and over 250,000 t are produced for industrial use annually. To ferment the milk sugar lactose, a cellodextrin transporter (CDT-1, which also transports lactose) and a β-glucosidase (GH1-1, which also acts as a β-galactosidase) from Neurospora crassa were expressed in a S. cerevisiae strain. A heterologous lactate dehydrogenase (encoded by ldhA) from the fungus Rhizopus oryzae was integrated into the CDT-1/GH1-1-expressing strain of S. cerevisiae. As a result, the engineered strain was able to produce lactic acid from purified lactose, whey, and store-bought milk. A lactic acid yield of 0.358g/g of lactose was achieved from whey fermentation, providing an initial proof of concept for the production of value-added chemicals from excess industrial whey using engineered yeast.
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana 61801; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana 61801.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Turner
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana 61801.
authors.forename: Eunbee
authors.initials: E
authors.lastname: Kim
authors.affiliation: Department of Food Science Technology, Chungnam National University, Daejeon 34134, South Korea.
authors.forename: ChangHoon
authors.initials: C
authors.lastname: Hwang
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana 61801; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana 61801.
authors.forename: Guo-Chang
authors.initials: GC
authors.lastname: Zhang
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana 61801; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana 61801.
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Liu
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana 61801; Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana 61801. Electronic address: ysjin@illinois.edu.
authors.forename: Yong-Su
authors.initials: YS
authors.lastname: Jin
mesh_terms: D000818:Animals; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism*; D008892:Milk / Q000382:microbiology; D030781:Organisms, Genetically Modified / Q000235:genetics / Q000378:metabolism; D012233:Rhizopus / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D000067796:Whey / Q000378:metabolism* / Q000382:microbiology
chemical_list: D005656:Fungal Proteins; D019344:Lactic Acid; D007770:L-Lactate Dehydrogenase; D007785:Lactose
keywords: lactic acid; lactose; whey; yeast