Aspergillus niger Secretes Citrate to Increase Iron Bioavailability
…or in other words…Aspergillus makes you anemic and gives you kidney stones.
The filamentous fungus Aspergillus niger has an innate ability to secrete organic acids in high quantities, and is essential as a biotechnological citrate producer. On glucose as carbon source, wild type A. niger secretes gluconate and oxalate as well as citrate. To inhibit by-production of gluconate and oxalate, A. niger citrate production requires pH ≤ 2.5 and the absence of manganese (Mn2+) ions, thereby enforcing overproduction of citrate instead. Further production conditions that have been reported to influence external citrate accumulation are, amongst others, the choice and concentrations of the carbon and nitrogen sources, and the concentrations of trace elements in the culture medium.
LEMON pH = 2.3
The purpose of this study was to investigate the effect of oral administration of manganese acetate on the kidneys and urinary bladder of Sprague-Dawley (SD) rats. Male and female SD rats (150 to 175 g), 6 weeks old, were administered varying doses of manganese acetate for 63 days by oral gavage. At the end of 63 days, 50% of the animals were sacrificed and kidney tissue was isolated and fixed for histopathological studies (study A). The remaining 50% were cross-mated and dosing ceased. Animals were sacrificed after 2 weeks (study B). Male treated animals were noted to have viscous, gritty urine in the urinary bladder, and the high-dose groups had urinary bladder stones (uroliths). Histopathologically, the most striking lesions were observed in the kidneys and prostate glands of male animals. Mild-to-moderate tubulointerstitial nephritis with tubular proteineous and glomerulosclerosis was observed in animals of all treatment groups. Urolithiasis in the urinary bladder was confirmed in 33% to 66% of treated animals. Female animals did not show a significant difference above controls in renal tissues. Results of this study suggest that male rats are more sensitive to the effects of high levels of manganese given orally than female rats and that the genitourinary structures represent target organs of toxicity.