ALIPHATIC ORGANIC ACIDS 135 



Table 1 (continued) 



Acid Organisms 



Glutaconic acid X Aspergillus niger (26) 



HOOC— CH=CH— CH 2 — COOH 



Dimethylpyruvic acid Aspergillus niger § (272, 438, 439) 



(CH 3 ) 2 — CH— CO— COOH 



Ethylene oxide Aspergillus jumigatus (67, 368); Monilia 



a,/3-dicarboxylic acid formosa, Penicillium viniferum (458) 



O 



/ \ 

 HOOC— CH— CH— COOH 



far as is now known, the accumulation of large amounts of the acid 

 is restricted to certain strains of Aspergillus spp. and Penicillium spp., 

 and many fungi yield no gluconate by classical isolation procedures 

 (321, 372,' 465). 



Because of the potential industrial importance of the process, the 

 conditions of gluconate synthesis by Aspergillus niger have been in- 

 tensively studied. It is found generally that a relatively high pH 

 favors the formation of gluconate over that of citrate (101, 221, 513). 

 Calcium carbonate is customarily added to the medium to control the 

 pH: interference with metabolism by precipitated calcium gluconate 

 can be minimized by the addition of boric acid or borax to the medium 

 (386). As in other acid syntheses, but to a more pronounced degree, 

 the accumulation of gluconate is favored by aeration (464, 554). It is 

 also favored by a relatively high glucose concentration (46, 269) and 

 a limiting amount of phosphate (269). Under appropriate conditions 

 almost complete conversion of glucose to gluconate occurs (221). 



The biochemical basis of gluconic acid formation is probably the 

 action of enzyme glucose aerodehydrogenase (glucose oxidase) (Chapter 

 7), although Dematium pullulans is reported to form gluconate (422) 

 and to lack the enzyme (212). The first product in the reaction is 

 glucono-8-lactone, which may be found in the medium with the free 

 acid (80). Gluconate is further utilized by fungi (46, 514), but the path 

 of metabolism is not known. 



The formation by Aspergillus niger of other hexonic acids — man- 

 nonic acid from mannose and galactonic acid from galactose — has 

 been reported (Table 1), but the process has not been studied further. 

 Penicillium chrysogenum forms lactobionic acid from lactose (151a). 



Glucuronic acid is reported to be formed in traces by fungi (Table 

 1), although an unequivocal identification is still lacking. Saccharic 

 acid is found in cultures of Aspergillus niger (126, 539). The appear- 



