Identification and characterization of putative xylose and cellobiose transporters in Aspergillus nidulans. Issue 1 (December 2016)

• Record Type: Journal Article
• Authors: Reis, Thaila; Lima, Pollyne; Parachin, Nádia; Mingossi, Fabiana; Castro Oliveira, Juliana; Ries, Laure; Goldman, Gustavo
• Is Part Of: Biotechnology for biofuels. Volume 9:Issue 1(2016)
• Page Start: 1
• Page End: 19
• Publication Date: 2016-12
• Subjects: Aspergillus nidulans -- Saccharomyces cerevisiae -- Xylose -- Cellobiose -- Sugar transport; Biotechnology -- Periodicals; Biomass energy -- Periodicals; Energy-Generating Resources -- Periodicals; 662.88
• DOI: 10.1186/s13068-016-0611-1
• Languages: English
• ISSNs: 1754-6834

Abstract

Abstract Background The conversion of lignocellulosic biomass to biofuels (second-generation biofuel production) is an environmentally friendlier alternative to petroleum-based energy sources. Enzymatic deconstruction of lignocellulose, catalyzed by filamentous fungi such asAspergillus nidulans, releases a mixture of mono- and polysaccharides, including hexose (glucose) and pentose (xylose) sugars, cellodextrins (cellobiose), and xylooligosaccharides (xylobiose). These sugars can subsequently be fermented by yeast cells to ethanol. One of the major drawbacks in this process lies in the inability of yeast, such asSaccharomyces cerevisiae, to successfully internalize sugars other than glucose. The aim of this study was, therefore, to screen the genome ofA. nidulans, which encodes a multitude of sugar transporters, for transporters able to internalize non-glucose sugars and characterize them when introduced intoS. cerevisiae . Results This work identified two proteins inA. nidulans, CltA and CltB, with roles in cellobiose transport and cellulose signaling, respectively. CltA, when introduced intoS. cerevisiae, conferred growth on low and high concentrations of cellobiose. Deletion ofcltB resulted in reduced growth and extracellular cellulase activity inA. nidulans in the presence of cellobiose. CltB, when introduced intoS. cerevisiae, was not able to confer growth on cellobiose, suggesting that this protein is a sensor rather than a transporter. However, we have shown that the introduction of additional functional copies of CltB increases the growth in the presence of low concentrations of cellobiose, strongly indicating CltB is able to transport cellobiose. Furthermore, a previously identified glucose transporter, HxtB, was also found to be a major xylose transporter inA. nidulans . InS. cerevisiae, HxtB conferred growth on xylose which was accompanied by ethanol production. Conclusions This work identified a cellobiose transporter, a xylose transporter, and a putative cellulose transceptor inA. nidulans . This is the first time that a sensor role for a protein inA. nidulans has been proposed. Both transporters are also able to transport glucose, highlighting the preference ofA. nidulans for this carbon source. This work provides a basis for future studies which aim at characterizing and/or genetically engineeringAspergillus spp. transporters, which, in addition to glucose, can also internalize other carbon sources, to improve transport and fermentation of non-glucose sugars inS. cerevisiae .