Overexpression of the Aspergillus niger GatA transporter leads to preferential use of D-galacturonic acid over D-xylose

Abstract

Pectin is a structural heteropolysaccharide of the primary cell walls of plants and as such is a significant fraction of agricultural waste residues that is currently insufficiently used. Its main component, D-galacturonic acid, is an attractive substrate for bioconversion. The complete metabolic pathway is present in the genome of Aspergillus niger, that is used in this study. The objective was to identify the D-galacturonic acid transporter in A. niger and to use this transporter to study D-galacturonic acid metabolism.We have functionally characterized the gene An14g04280 that encodes the D-galacturonic acid transporter in A. niger. In a mixed sugar fermentation it was found that the An14g04280 overexpression strain, in contrast to the parent control strain, has a preference for D-galacturonic acid over D-xylose as substrate. Overexpression of this transporter in A. niger resulted in a strong increase of D-galacturonic acid uptake and induction of the D-galacturonic acid reductase activity, suggesting a metabolite controlled regulation of the endogenous D-galacturonic acid catabolic pathway.

An Evolutionarily Conserved Transcriptional Activator-Repressor Module Controls Expression of Genes for D-Galacturonic Acid Utilization inAspergillus niger

“…Of these seven transporter-encoding genes, only GatA has been studied in detail and shown to be able to transport GA (Sloothaak et al 2014). Apart from the genes encoding extracellular enzymes (16), transporters (seven), and enzymes possibly involved in GA catabolism (nine), the remaining five genes in this group encode proteins with unknown functions or with similarities to known proteins that, for now, cannot be directly linked to GA metabolism.…”

“…It is interesting to note that among the genes listed in Figure 3 and Table 3 that are upregulated in the DgaaX, some of them (NRRL3_00957 and NRRL3_00958; NRRL3_09862 and NRRL3_09863; NRRL3_03291 and NRRL3_03292) are clustered. Except for NRRL3_00958, which encodes a GA-specific transporter (Sloothaak et al 2014), the possible role of these genes in pectin degradation is currently unknown.…”

The interaction of induction and repression mechanisms in the regulation of galacturonic acid-induced genes in Aspergillus niger

“…The genes encoding these enzymes (gaaA, gaaB, gaaC, and gaaD have been identified and the biochemical properties of the enzymes have been determined (Kuorelahti et al, 2005Hilditch et al, 2007;Mojzita et al, 2010;Wiebe et al, 2010;Liepins et al, 2006;Zhang et al, 2011;Kuivanen et al, 2012). Specific sugar transporters that are able to transport GA over the plasma membrane have recently been identified and characterised in Neurospora crassa (Benz et al, 2014) as well as in A. niger (Sloothaak et al, 2014) and Botrytis cinerea (Zhang et al, 2014). The transporters identified in these studies are phylogenetically related and probably represent a subfamily of GA-specific transporters (Zhang et al, 2014).…”

Organic acid production in Aspergillus niger and other filamentous fungi

“…These yeast mutant strains, unable to grow on glucose, fructose, mannose and galactose as a single carbon source, have also subsequently been used as tools for the functional characterisation of sugar transporters from other fungal species (Colabardini et al, 2014;dos Reis et al, 2013;Du et al, 2010;Leandro et al, 2013;Polidori et al, 2007;Saloheimo et al, 2007;Vankuyk PA et al, 2004;Wahl et al, 2010) In contrast to S. cerevisiae, the only functionally validated sugar transporters in A. niger are the recently identified D-galacturonic acid transporter GatA (Martens-Uzunova and Schaap, 2008;Sloothaak et al, 2014), two fructose transporters (Coelho et al, 2013) and the high-affinity sugar/H + symporter MstA (Vankuyk PA et al, 2004). Furthermore, transcriptional data for the A. niger mstC gene suggests that it encodes a low-affinity glucose transporter (Jørgensen et al, 2007), but no experimental data supporting its role as a functional sugar transporter is publicly available.…”

“…Regarding the uptake of the specific pectin components, transporters responsible for the uptake of D-galacturonic acid have been reported in A. niger and Neurospora crassa (Benz et al, 2014;Sloothaak et al, 2014). However, not a single L-rhamnose transporter has been identified in fungi, or in any other eukaryotic organism.…”