title: Identification and characterization of putative xylose and cellobiose transporters inAspergillus nidulans.
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 ofcltBresulted in reduced growth and extracellular cellulase activity inA. nidulansin 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. nidulanshas been proposed. Both transporters are also able to transport glucose, highlighting the preference ofA. nidulansfor this carbon source. This work provides a basis for future studies which aim at characterizing and/or genetically engineeringAspergillusspp. transporters, which, in addition to glucose, can also internalize other carbon sources, to improve transport and fermentation of non-glucose sugars inS. cerevisiae.
authors.affiliation: Departamento de Ciências Farmacêuticas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N, Ribeirão Preto, SP CEP 14040-903 Brazil.
authors.forename: Thaila Fernanda
authors.initials: TF
authors.lastname: Dos Reis
authors.affiliation: Departamento de Biologia Celular, Instituto de Biologia, Universidade de Brasília, Brasília, CEP 70910-900 Brazil.
authors.forename: Pollyne Borborema Almeida
authors.initials: PB
authors.lastname: de Lima
authors.affiliation: Departamento de Biologia Celular, Instituto de Biologia, Universidade de Brasília, Brasília, CEP 70910-900 Brazil.
authors.forename: Nádia Skorupa
authors.initials: NS
authors.lastname: Parachin
authors.affiliation: Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Campinas, Brazil.
authors.forename: Fabiana Bombonato
authors.initials: FB
authors.lastname: Mingossi
authors.affiliation: Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Campinas, Brazil.
authors.forename: Juliana Velasco
authors.initials: JV
authors.lastname: de Castro Oliveira
authors.affiliation: Departamento de Ciências Farmacêuticas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N, Ribeirão Preto, SP CEP 14040-903 Brazil.
authors.forename: Laure Nicolas Annick
authors.initials: LN
authors.lastname: Ries
authors.affiliation: Departamento de Ciências Farmacêuticas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café S/N, Ribeirão Preto, SP CEP 14040-903 Brazil.
authors.forename: Gustavo Henrique
authors.initials: GH
authors.lastname: Goldman
keywords: Aspergillus nidulans; Cellobiose; Saccharomyces cerevisiae; Sugar transport; Xylose