Journal of General Microbiology (1 989), 135, 2 163-2 17 1. Printed in Great Britain 2163 L- Arabinose and D-Xylose Catabolism in Aspergillus niger By C. F. B. WITTEVEEN,' R. BUSINK,' P. VAN DE VONDERVOORT,' C. DIJKEMA,2 K. SWART' AND J. VISSER1* 6703 HA Wageningen, The Netherlands Departments oj Genetics' and Molecular Physics, Agricultural University, Dreyenlaan 2, (Received 18 January 1989; revised 3 May 1989; accepted 10 May 1989) ~~ ~~ ~- ~ ~~ ~~ ~ A mutant of Aspergillus niger unable to grow on D-XylOSe and L-arabinose has been isolated. Genetic analysis revealed that the mutation is located on linkage group IV. Enzymic analysis revealed a deficiency in D-XylUlOSe kinase activity. After transfer of growing mycelium to a medium containing either D-xylose or L-arabinose, the mutant accumulates large amounts of arabitol and xylitol, as shown by I3C NMR spectroscopy. These data and an analysis of enzyme activities induced by D-XylOSe and L-arabinose in the wild-type strain led to the following catabolic pathway for D-xylose : D-xylose - xylitol - D-xylulose - D-xylulose 5-phosphate; and for L-arabinose : L-arabinose - L-arabitol - L-xylulose - xylitol - D-xylulose - D-xylulose 5-phosphate. The reduction steps of the sugars to the corresponding polyols are all NADPH dependent. The oxidation steps of the polyols to the sugars are all NAD+ dependent. Fractionation of cell-free extracts gave information about the specificity of the enzymes and showed that all the reactions are catalysed by different enzymes. INTRODUCTION Pentose metabolism in filamentous fungi has received little attention since the early reports on this subject by Chiang and coworkers (Chiang et al., 1958; Chiang & Knight, 1959, 1960a, b, 1961).Later, Hankinson (1974) studied, in Aspergillusnidulans, two classes of mutants,pppA and pppB, which were disturbed in the pentose phosphate pathway. These mutants showed no or decreased growth on D-xylose and L-arabinose. D-Xylose metabolism has been studied intensively in yeasts, especially in relation to the production of ethanol under anaerobic conditions (Jeffries, 1985). L-Arabinose catabolism, however, has received little attention. Most organisms convert both D-xylose and L-arabinose to D-xylulose 5-phosphate, although different pathways are used by different organisms. A remarkable difference between bacteria and most fungi is the way in which they convert D-xylose to D-xylulose. Bacteria usually use an isomerase, whereas fungi reduce D-XylOSe to xylitol which is subsequently oxidized to D-XylUlOSe (Jeffries, 1983). For L-arabinose breakdown several pathways have been described. The reduction-oxidation pathway described for Penicillium chrysogenumby Chiang & Knight (1961) contains the following steps : an NADPH-dependent reduction to L-arabitol, oxidation to L- xylulose (NAD+), reduction to xylitol (NADPH) and oxidation to D-xylulose (NAD+). The principle of this catabolic sequence is comparable to the D-xylose pathway found in fungi (Chiang & Knight, 1960b). Aspergillusniger grows well on pentose substrates and it can also hydrolyse polymers, such as hemicellulose, which contain these sugars. Pentoses are presumably important substrates for this fungus, and since for Aspergillus little information is available on this subject, this study on catabolism of L-arabinose and D-XylOSe was initiated. METHODS Biochemicals. The pent(ul)oses, pentitols and ~-xylulose-5-phosphate were purchased from Sigma. NAD(P)+, NAD(P)H, ATP, glucose 6-phosphate, 6-phosphogluconate, phosphoenolpyruvate and enzymes were supplied by 0001-5356 0 1989 SGM