$2 Perspecfives in Microbiology 



ous property of 5. hrevicaulis, the arsenic fungus, which 

 it displays to a conspicuous (or should we say, lethal?) 

 degree, exemplifies the thesis presented earlier, to wit: 

 in metabolism, the unusual is not only the outpost, but 

 the signpost of the usual — a metabolic model, as it were. 



Earlier studies on the fungi might have led to results 

 in still another area, namely, attainment of our modern 

 conceptual formulation of the mechanism of, and the cyclic 

 nature of, respiration and carbohydrate oxidation. A per- 

 spective appraisal reveals that individual strains or species 

 of fungi acting on glucose accumulate, under appropriate 

 conditions, a preponderance of one carboxylic acid, gen- 

 erally accompanied by lesser amounts of other acids. Thus 

 we have citric-acid-accumulating fungi; we have itaconic 

 acid fungi; we have fungi accumulating fumaric acid and 

 its relatives, succinic and malic acids; we have fungi pro- 

 ducing oxalic acid, with its acetic and giycolic acid equiva- 

 lents; we have fungi accumulating ethanol, with its acetic 

 acid equivalent. These distinctive fungus processes were 

 recognized as far back as the 1890's. We know today that 

 all these fungi conduct fundamentally the same type of 

 oxidation of the carbohydrate, that the oxidation is the 

 aerobic respiratory process of the fungi, that with one or 

 two exceptions all these organic acids are formed by all 

 the fungi so far examined, that the unique accumulations 

 represent blockage of the oxidative pathway at different 

 points, and that the process is cyclic — the Krebs tricar- 

 boxylic acid cycle. 



Thus, for a half-century before the conceptual formula- 

 tion and the experimental demonstration by Szent-Gyorgi 

 and by Krebs of the role of dicarboxylic and tricarboxylic 

 acids in aerobic respiration, the signposts marking the way 

 were clearly visible, albeit unrecognizable, in the fungi. 

 The same might be said for the so-called gluconic acid 

 shunt, because it was in 1922 that Molliard discovered 

 that certain fungi accumulate distinctive amounts of glu- 



