A Possible Role of Hydroxypyruvic Acid Reductase In Growth of A. niger

In a study of growth and differentiation in Aspergillus niger it has been previously shown that while the operation of the citric acid cycle is essential to the development of spores, growth of the hyphae is dependent on a metabolic pathway that seems to diverge from glycolysis (Embden-Meyerhof), and not upon the pyruvic dehydrogenation system and the reactions of the tricarboxylic acid cycle(1).

With the culture method described below, this mold completes its growth cycle in 80 hours. The lag phase continues to the 20th hour; logarithmic phase begins then and continues until the 58-60th hour. At this point spore formation begins and continues rapidly. Mold pad weight begins to decline at the 80th hour. In a previous paper it was shown that the 40-52 hour interval was critical for spore formation and that the purine analog, 6-ethylthiopurine, if present in the growth medium during this interval would selectively inhibit subsequent spore formation (at 60th hour) without any effect on growth of hyphae or conidiophores. In this paper attention will be focused on the 20-40th hour interval, that is the period when mycelial growth is dominant, prior to conidiophore (stalk) formation. This latter process predominates during the subsequent 40-60 hour period and is specifically inhibited by 6-hydroxy-2mercaptopulrine(2).

In earlier papers the production of hydroxypyruvic acid by this mold was reported and it was postulated that this acid served a precursor for a series of reactions necessary for hyphal growth (3,4). The data presented below concern further observations on the relationship between hyphal growth and the metabolism of ths acid

Materials and methods. The medium routinely used had the following composition: glucose, 45.0g; N_aNO₃, 4.5 g; KH₂PO₄, 3.0 g; KCl, 0.75 g; MgSO₄ · 7H₂O