Identification of an l-Arabitol Transporter from Aspergillus niger

Abstract

l-arabitol is an intermediate of the pentose catabolic pathway in fungi but can also be used as a carbon source by many fungi, suggesting the presence of transporters for this polyol. In this study, an l-arabitol transporter, LatA, was identified in Aspergillus niger. Growth and expression profiles as well as sugar consumption analysis indicated that LatA only imports l-arabitol and is regulated by the arabinanolytic transcriptional activator AraR. Moreover, l-arabitol production from wheat bran was increased in a metabolically engineered A. niger mutant by the deletion of latA, indicating its potential for improving l-arabitol-producing cell factories. Phylogenetic analysis showed that homologs of LatA are widely conserved in fungi.

Keywords: Aspergillus niger; l-arabitol; polyol; sugar beet pulp; transporter; wheat bran.

Figure 1

Expression profiles of putative sugar transporters in A. niger on diverse carbon sources [21]. Protein IDs of A. niger NRRL3 are shown in the figure, and numbers in brackets reflect protein IDs from A. niger CBS 513.88. The color code represents averaged and logged expression values (FPKM + 1) of replicates. The heat map was drawn using GraphPad Prism (https://www.graphpad.com/, accessed on 11 January 2023). Group A and I refer to the phylogenetic grouping of transporters, as described previously [21].

Figure 2

Phenotypic analysis of mutant and reference strains. (A) Growth profiling of the A. niger reference strain N593 Δku70 and two single deletion mutants Δ05659 and ΔlatA on l-arabitol. (B) Growth profiling of the A. niger reference strain N593 Δku70 and ΔlatA on different sugars and polyols.

Figure 3

Consumption of sugars and polyols by the A. niger reference strain and ΔlatA in liquid cultures supplemented with l-arabitol (A), l-arabinose (B), xylitol (C), d-xylose (D), galactitol (E) and d-galactose (F) as the substrates. The error bars indicate the standard deviation between biological triplicates.

Figure 4

Extracellular xylitol and l-arabitol concentrations from wheat bran ((A) and (B), respectively) and sugar beet pulp ((C) and (D), respectively) cultures of the A. niger mutant strains ΔladAΔxdhAΔsdhA and ΔladAΔxdhAΔsdhAΔlatA. The error bars indicate the standard deviation between biological triplicates.

Figure 5

Unrooted phylogenetic tree of homologs of LatA from A. niger. The tree includes a specific l-arabinose transporter Lat2 from A. monospora (shown in larger font and black), the characterized l-arabitol importer LatA in A. niger (shown in larger font and boldface) and homologs of LatA in selected fungi. Bootstrap values are indicated on the nodes, which are supported by the Neighbor joining method. Colors represent the fungal taxonomic groups. Red = Eurotiomycetes, blue = Sordariomycetes, grey = Dothideomycetes. Numbers in brackets reflect the protein ID from JGI MycoCosm [38].