Deletion of <i>flbA</i> Results in Increased Secretome Complexity and Reduced Secretion Heterogeneity in Colonies of <i>Aspergillus niger</i>

Aspergillus niger is a cell factory for the production of enzymes. This fungus secretes proteins in the central part and at the periphery of the colony. The sporulating zone of the colony overlapped with the nonsecreting subperipheral zone, indicating that sporulation inhibits protein secretion. Indeed, strain ΔflbA that is affected early in the sporulation program secreted proteins throughout the colony. In contrast, the ΔbrlA strain that initiates but not completes sporulation did not show altered spatial secretion. The secretome of 5 concentric zones of xylose-grown ΔflbA colonies was assessed by quantitative proteomics. In total 138 proteins with a signal sequence for secretion were identified in the medium of ΔflbA colonies. Of these, 18 proteins had never been reported to be part of the secretome of A. niger, while 101 proteins had previously not been identified in the culture medium of xylose-grown wild type colonies. Taken together, inactivation of flbA results in spatial changes in secretion and in a more complex secretome. The latter may be explained by the fact that strain ΔflbA has a thinner cell wall compared to the wild type, enabling efficient release of proteins. These results are of interest to improve A. niger as a cell factory.黑曲霉（Aspergillus niger）是用于酶类生产的细胞工厂。该真菌可在菌落的中心区域与外围区域分泌蛋白质。菌落的产孢区与不分泌蛋白质的亚外围区域存在重叠，这表明产孢过程会抑制蛋白质分泌。确实，早期在产孢程序中受影响的ΔflbA菌株可在整个菌落范围内分泌蛋白质。与之相反，能够启动但无法完成产孢的ΔbrlA菌株，其空间分泌模式并未发生改变。研究通过定量蛋白质组学（quantitative proteomics）分析了木糖培养的ΔflbA菌落的5个同心区域的分泌组（secretome）。总计在ΔflbA菌落的培养基中鉴定出138种带有分泌信号肽的蛋白质。其中，18种蛋白质此前从未被报道属于黑曲霉的分泌组，另有101种蛋白质此前未在木糖培养的野生型菌落的培养基中被鉴定到。综上，flbA基因的失活会导致分泌模式发生空间改变，并使分泌组更为复杂。这一现象或许可归因于ΔflbA菌株的细胞壁相较于野生型更薄，从而能够更高效地释放蛋白质。上述研究结果对于优化黑曲霉作为细胞工厂的应用具有重要价值。