Burgstaller W, Zanella A, Schinner F
Christian Doppler Laboratory of Environmental Biotechnology, Innsbruck, Austria.
Arch Microbiol. 1994;161(1):75-81. doi: 10.1007/BF00248896.
Organic acids excreted by filamentous fungi may be used to win metals from industrial secondary raw materials. For a future commercial use a high production rate of organic acids is necessary. The conditions under which the commercially used fungus Aspergillus niger excretes high amounts of citric acid can not be maintained in metal leaching processes. However, Penicillium simplicissimum showed an enhanced citric acid efflux in the presence of an industrial filter dust containing 50% zinc oxide. Because Good buffers of high molarity were able to mimic the effect of zinc oxide, the high buffering capacity of zinc oxide and not an effect of the zinc ions was held responsible for the enhanced citric acid efflux. The presence of ammonium and trace elements reduced this buffer-stimulated citric acid efflux, whereas the plant hormone auxine canceled this reduction. This citric acid efflux was influenced by a depolarization of the membrane: the freely permeable compound tetraphenylphosphoniumbromide decreased the citric acid efflux, without decreasing intracellular citric acid or consumption of glucose and oxygen. Vanadate, an inhibitor of the plasma membrane H(+)-ATPase also reduced the buffer-stimulated citric acid efllux. The role of the efflux of citrate anions as an alternative charge balancing ion flow in case of impaired backflow of extruded protons because of a high extracellular buffering capacity is discussed.
丝状真菌分泌的有机酸可用于从工业二次原料中提取金属。为了未来的商业用途，有必要提高有机酸的生产率。在金属浸出过程中，无法维持商业使用的黑曲霉分泌大量柠檬酸的条件。然而，简单青霉在含有50%氧化锌的工业滤尘存在下，柠檬酸外排增强。由于高摩尔浓度的良好缓冲剂能够模拟氧化锌的作用，因此认为氧化锌的高缓冲能力而非锌离子的作用导致了柠檬酸外排增强。铵和微量元素的存在降低了这种缓冲剂刺激的柠檬酸外排，而植物激素生长素消除了这种降低。这种柠檬酸外排受到膜去极化的影响：自由渗透的化合物溴化四苯基膦降低了柠檬酸外排，而不降低细胞内柠檬酸或葡萄糖和氧气的消耗。钒酸盐是质膜H(+)-ATP酶的抑制剂，也降低了缓冲剂刺激的柠檬酸外排。讨论了在由于高细胞外缓冲能力导致挤出质子回流受损的情况下，柠檬酸根阴离子外排作为替代电荷平衡离子流的作用。
