Abstract: | - Some recent works on the formation of oxalic acid by variousfungi are critically considered.
- The present work deals withthe role of oxalic acid in the metabolismof Aspergillus niger.
- When glucose solutions were supplied to preformed mats ofthefungus oxalic acid accumulated, attaining an equilibriumlevelwhich was not exceeded despite the presence of a considerableconcentration of glucose.
- When the glucose supplies were depletedthe oxalic acid concentrationfell steeply to a low level.
- Theconcentration of oxalic acid was dependent on the glucoseconcentration.In three separate series of experiments it wasshown that theoxalic acid concentration diminished with increasingglucoseconcentration.
- Similar results were obtained when the cultureswere rearedfrom spores on culture solutions with the normalamounts ofnutrient salts but different glucose concentrations.
- In all cases the CO2 output increased with the glucose concentration.
- When cultures were supplied with glucose+oxalic acid, theconcentrationof the latter fell steeply to the equilibriumlevel attainedon glucose only. In a culture receiving glucose+oxalicacid,with the oxalic acid concentration somewhat below thenormalequilibrium concentration, the formation of oxalic acidfromthe glucose ceased as soon as the equilibrium level hadbeenattained.
- When 1 per cent. oxalic acid only was suppliedto the fungusthe concentration gradually diminished to a lowlevel. When3 per cent. oxalic acid was supplied the rate ofacid utilizationsoon fell to low value.
- In several experimentsit was shown that the rate of CO2 outputwas higher from culturessupplied with glucose+excess oxalicacid than from culturessupplied with glucose only.
- The rate of oxalic acid carbonloss was always below that ofthe CO2 carbon output both incultures supplied with oxalicacid only and in cultures receivingglucose+oxalic acid.
- The cultures were incapable of utilizingneutral sodium oxalateand the presence of this substance hadno effecft on the ofCO2 output.
- The results indicate thatthe utilization of oxalic acid isassociated with the liberationof at least an equivalent amountof CO2.
- It is suggested thatthe utilization of oxalic acid is promotedby the presence ofglucose, thus accounting for the lower oxalicacid concentrationsand higher rates of CO2 output of cultureswith higher glucoseconcentrations.
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