kluyver's contributions to microbiology and biochemistry 



Duclaux has introduced the suggestive term, "products of suffering" ' 



(P- 6 9 )-* 



Now, the experiments of Molliard had shown that the mould, Asp. 

 niger, which can oxidize sugar without causing the accumulation of 

 any acid whatever, may be induced to form considerable quantities 

 of gluconic, citric, or oxalic acid by growing it in a culture medium 

 with drastically reduced nitrogen, phosphate, or potassium content. 

 'Consequently', continued Kluyver and Perquin, ' it was obvious that 

 for this mould at least the industrially important acid production is 

 not a physiological, but rather a pathological process. Viewed in this 

 light the inadequacy of the methods hitherto used in the study of mould 

 metabolism hardly needs commentary. It must be evident how utterly 

 heterogeneous are the conditions under which the individual cells exist 

 in a mycelial pad growing on the surface of a liquid culture medium. 

 Whereas the cells in the upper layers are bathed in the oxygen of the 

 atmosphere, they must depend for their supply of nutrients on the dif- 

 fusion of the latter through the mycelium, and only that fraction which 

 is not absorbed by the cells lower down will reach them. Conversely, 

 the latter type of cells swim in a substrate-rich environment, but have 

 access to very limited amounts of oxygen because this gas is largely 

 consumed in the upper layers. Between these two extremes all possible 

 intermediate stages exist. It must be realized that part of the cells may 

 be so poorly nourished that they become considerably weakened, and 

 may even undergo autolysis. 



'In connexion with results such as those of Molliard's this implies 

 that the metabolism of the individual cells in the mycelium will ex- 

 hibit pronounced mutual differences, and that the customary anal- 

 ysis of the over-all processes in such a liquid culture can only provide 

 information concerning the combined results of the diverse metabolic 

 processes that proceed under the influence of the various cell types. 



'If one further keeps in mind that the structure of the mycelial mat 



* After the discovery of A. suboxydans with its intrinsically low oxidative capac- 

 ity, the transient accumulation of incomplete oxidation products in liquid cultures 

 of A. xylinum was attributed by Visser 't Hooft [1925] to the poor oxygen provision 

 underneath the thick pellicle which is the characteristic growth form of this organ- 

 ism. This notion is supported by the fact that on glucose-calcium carbonate-agar 

 plates A. xylinum does not even produce detectible amounts of acid. Kluyver used 

 to refer to this bacterium as a 'physically conditioned sorbose bacterium', in con- 

 trast to the 'ideal sorbose bacterium' which is, of course, A. suboxydans. 



J 35 



