PRODUCTS OF THE LOWER FUNGI 293 



obtained. Lowering the nitrogen supply raises the yield 

 of citric acid, whilst high nitrogen and phosphate with 

 low potassium gives rise to good yields of oxalic acid. 

 The process is worked industrially in the United States, 

 using P. luteum (variety ruhrisclerotium) . 



In view of the high yields obtained from glucose it is 

 considered that the formation of gluconic acid is a direct 

 oxidation of glucose by the enzyme glucose -oxidase and 

 is quite independent of the reactions by which citric acid 

 is formed. This is further borne out by the facts that 

 there is no correlation between the times of maximum 

 formation of the two acids and that there is no formation 

 of citric acid from gluconic acid. Some, but not all, 

 other sugars are oxidised in a similar way by Penicillium 

 luteum to give the corresponding acids ; thus mannose is 

 oxidised to mannonic acid and xylose to xylonic acid, 

 but galactose and arabinose are not affected, although 

 they may be oxidised by other fungi. 



Lactic Acid. — Rhizopus oryzce, when grown with urea 

 as a source of nitrogen in surface culture or as an aerated, 

 submerged growth in a rotating di'um, may convert 

 up to 75 per cent, of the glucose utilised into c^-lactic 

 acid. Other species of Rhizopus produce large quantities 

 of Z-lactic acid from glucose, together with small quantities 

 of formic acid, acetic acid, fumaric acid, /-malic acid, 

 succinic acid and ethyl alcohol. 



Fumaric and Malic Acids. — These acids are not very 

 common mould products but are formed in comparatively 

 low yields by the action of one or two species of Rhizopus 

 and Aspergillus from glucose, fructose, galactose or 

 arabinose. It is possible that they are normally inter- 

 mediates in the formation of other acids. 



Succinic Acid. — Succinic acid is a rare product of 

 mould metaboHsm, although it is fairly commonly pro- 

 duced by yeasts and bacteria. It is probably formed by 

 all three tvpes of organism by the breakdown of the amino - 

 acid, glutamic acid, COOH.CHg.CHa.CHNHg.COOH, 



