Cellobionic acid utilization: from Neurospora crassa to Saccharomyces cerevisiae.
BACKGROUND
Economical production of fuels and chemicals from plant biomass requires the efficient use of sugars derived from the plant cell wall. Neurospora crassa, a model lignocellulosic degrading fungus, is capable of breaking down the complex structure of the plant cell wall. In addition to cellulases and hemicellulases, N. crassa secretes lytic polysaccharide monooxygenases (LPMOs), which cleave cellulose by generating oxidized sugars-particularly aldonic acids. However, the strategies N. crassa employs to utilize these sugars are unknown.


RESULTS
We identified an aldonic acid utilization pathway in N. crassa, comprised of an extracellular hydrolase (NCU08755), cellobionic acid transporter (CBT-1, NCU05853) and cellobionic acid phosphorylase (CAP, NCU09425). Extracellular cellobionic acid could be imported directly by CBT-1 or cleaved to gluconic acid and glucose by a β-glucosidase (NCU08755) outside the cells. Intracellular cellobionic acid was further cleaved to glucose 1-phosphate and gluconic acid by CAP. However, it remains unclear how N. crassa utilizes extracellular gluconic acid. The aldonic acid pathway was successfully implemented in Saccharomyces cerevisiae when N. crassa gluconokinase was co-expressed, resulting in cellobionic acid consumption in both aerobic and anaerobic conditions.


CONCLUSIONS
We successfully identified a branched aldonic acid utilization pathway in N. crassa and transferred its essential components into S. cerevisiae, a robust industrial microorganism.
Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.
Xin
X
Li
Department of Plant and Microbial Biology, University of California, Berkeley, CA USA.
Kulika
K
Chomvong
Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.
Vivian Yaci
VY
Yu
Department of Chemistry, University of California, Berkeley, CA USA.
Julie M
JM
Liang
Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.
Yuping
Y
Lin
Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.|Department of Chemistry, University of California, Berkeley, CA USA.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA.
Jamie H D
JHD
Cate
AA9; Aldonic acid; Biofuels; Cellobionic acid; LPMO; Metabolic engineering; Phosphorylase; Transporter; β-glucosidase