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Background  Galactofuranose (Gal f )-containing glycoconjugates are present in numerous microbes, including filamentous fungi where they are important for morphology, virulence and maintaining cell wall integrity. The incorporation of Gal f -residues into galactomannan, galactomannoproteins and glycolipids is carried out by Golgi-localized Gal f  transferases. The nucleotide sugar donor used by these transferases (UDP-Gal f ) is produced in the cytoplasm and has to be transported to the lumen of the Golgi by a dedicated nucleotide sugar transporter.    Methods  Based on homology with recently identified UDP-Gal f -transporters in  A. fumigatus  and  A. nidulans , two putative UDP-Gal f -transporters in  A. niger  were found. Their function and localization was determined by gene deletions and GFP-tagging studies, respectively.    Results  The two putative UDP-Gal f -transporters in  A. niger  are homologous to each other and are predicted to contain eleven transmembrane domains (UgtA) or ten transmembrane domains (UgtB) due to a reduced length of the C-terminal part of the UgtB protein. The presence of two putative UDP-Gal f -transporters in the genome was not unique for  A. niger.  From the twenty Aspergillus species analysed, nine species contained two additional putative UDP-Gal f -transporters. Three of the nine species were outside the  Aspergillus section nigri , indication an early duplication of UDP-Gal f -transporters and subsequent loss of the UgtB copy in several aspergilli. Deletion analysis of the single and double mutants in  A. niger  indicated that the two putative UDP-Gal f -transporters (named UgtA and UgtB) have a redundant function in UDP-Gal f -transport as only the double mutant displayed a Gal f- negative phenotype. The Gal f -negative phenotype of the double mutant could be complemented by expressing either CFP-UgtA or CFP-UgtB fusion proteins from their endogenous promoters, indicating that both CFP-tagged proteins are functional. Both Ugt proteins co-localize with each other as well as with the GDP-mannose nucleotide transporter, as was demonstrated by fluorescence microscopy, thereby confirming their predicted localization in the Golgi.    Conclusion   A. niger  contains two genes encoding UDP-Gal f -transporters. Deletion and localization studies indicate that UgtA and UgtB have redundant functions in the biosynthesis of Gal f -containing glycoconjugates.    Electronic supplementary material  The online version of this article (doi:10.1186/s12866-015-0541-2) contains supplementary material, which is available to authorized users.

Identification and functional analysis of two Golgi-localized UDP-galactofuranose transporters with overlapping functions in Aspergillus niger