Morphology Manipulating And Reason Of Hypoxia Toxicity Of Itaconic Acid Production In Aspergillus Terreus

Filamentous fungal fermentation is widely used to produce valuable primary andsecondary metabolites such as organic acids, enzymes and antibiotics. One of the mostinteresting and difficult topics of filamentous fungi is to enhance the metabolite productionand study the physiological mechanism of insufficient production. Using itaconic acid （IA）production by Aspergillus terreus FMME033as a research model, the itaconic acidproduction was increased by optimizing the fermentation conditions and manipulatingmorphology in A. terreus. Furthermore, the reason for insufficient oxygen lead to insufficientproduction of itaconic acid was analysed. The main results were described as follows:1. The biosynthesis of itaconic acid is very dependent on the composition of the culturemedium and environmental conditions. The optimized initial pH was3.0. Thecomposition of an optimized medium for the production of itaconic acid contained （g/L）:glucose80,（NH₄）₂SO₄4, corn steep liquor power3, MgSO₄·7H₂O0.11, FeSO₄·7H₂O0.04, ZnSO₄·7H₂O0.05. As a result, the titer of itaconic acid was28.2g/L, and this valuewas one time higher than that of initial culture condition before optimization.2. An additional important factor for successful itaconic acid fermentation in submergedculture is the morphology of A. terreus. Our results demonstrated the following:（1） Threemorphologies （predominating dispersed mycelia morphologies, predominating clumpmorphologies, predominating pellet morphologies） of A. terreus were formed and higheritaconic acid production during predominating clump morphologies of A. terreus.（2） Therelationships between clump diameter and itaconic acid production were established,demonstrating that the yield of IA on DCW （R²=0.9809） and yield of glucose on DCW（R²=0.9421） were closely correlated with clump diameter. The optimal clump diameterrange for higher IA production was0.40-0.50mm. The yield of IA on DCW and the yieldof glucose on DCW were35.4%and27.5%higher than the corresponding values of thecontrol, respectively.（3） Furthermore, scale up from shake flasks to a7-L stirred tankbioreactor was successfully achieved based on the quantitative relationship. The clumpdiameter was controlled at0.45mm by manipulating the mechanical stress and the yieldof IA on DCW and the yield of glucose on DCW were increased by25.1%and16.3%,respectively. The results demonstrated that optimal productivity correlates closely with aspecific fungal morphology.3. One of the most important characteristics of the itaconic acid fermentation is the sensitivityof itaconic acid fermentation process to hypoxia. Our results demonstrated the following:using continuous shaking culture as a control, stopping shaking for5min resulted in thelevel of ROS increased transiently. Then the carbonylation level increased greatly andreached a maximum at40h, which was1.7times higher than the control. After a5minbreak in shaking, the sporangium became larger and more than the control. Aconitasespecific activity declined greatly and reached a minimum at40h, which was6.9%of thecontrol. At the end of fermentation, stopping shaking for5min resulted in a54.9%（itaconic acid）、56.9%（glucose consumption） and76.6%（final dry cell weight） of the control respectively. It is suggested that hypoxia stress led to an increase in the content ofoxidative damaged protein and then prevented IA production.d da...