The Influence of some trace-elements on the Growth of Aspergillus niger and on the citric acid Fermentation

S t e i n b e r g (1935) and L u n d (1953) found that the growth of Aspergillus niger is influenced by copper. O r 1 o v et al. (1968) have further observed that 10.0% solution of copper sulphate increases markedly the yield of citric acid when molasses is employed as substrate. T o m l i n s o n et al (1950) studied the influence of Zn, Fe, Mn and Cu on the production of citric acid and observed that zinc and iron are essential trace-elements for the maximum yield of citric acid. The results of study relating to the influence of trace-elements on the production of citric acid are apparently conflicting. Whit some samples of A. niger, E r k a m a and co-workers (1949) observed that iron and zinc accelerate the formation of citric acid, while with other samples of A. niger iron and zinc do not appear to be favourable for the good yield of citric acid. This contradictory finding in citric acid fermentation has been ascribed to the difference in strains of A. niger. This finding was also supported by Q u i 1 c o and D i c a p u a (1932). P e r l m a n (1946) observed that the optimum concentration of a particular trace-element changes with the strain of A. niger selected. He noted that the addition of 0.10 mg. of iron per litre to one medium was optimum for the yield of citric acid in the case of A niger 62, while a concentration of 1.0 mg. of iron per litre was optimum for A. niger 69, 70 and 72. It was also reported that molybdenum, copper and zinc inhibited the production of citric acid. W a t a r u (1966) observed that the addition of 0.5% H3BO3 gave good yield of citric acid. As a result of such interesting and conflicting observations, the role of trace-elements in the growth and activity of the micro-organisms has been the subject of much investigation. The present study deals with an investigation made to evaluate the citric acid producing power of four trace-elements (Lanthanum sulphate, Zirconium sulphate, Praseodymium sulphate and Uranium sulphate).