Microbial valorization of plant biomass is a key target in bioeconomy. A promising candidate for consolidated bioprocessing is the dimorphic fungus Ustilago maydis. It harbors hydrolytic enzymes to degrade biomass components and naturally produces valuable secondary metabolites like itaconic acid, malic acid or glycolipids. However, hydrolytic enzymes are mainly expressed in the hyphal form. This type of morphology should be prevented in industrial fermentation processes. Genetic activation of these enzymes can enable growth on cognate substrates also in the yeast form. Here, strains were engineered for growth on polygalacturonic acid as major component of pectin. Besides activation of intrinsic enzymes, supplementation with heterologous genes for potent enzymes was tested. The presence of an unconventional secretion pathway allowed exploiting fungal and bacterial enzymes. Growth of the engineered strains was evaluated by a recently developed method for online determination of residual substrates based on the respiration activity. This enabled the quantification of the overall consumed substrate as a key asset for the assessment of the enzyme degradation potential even on polymeric substrates. Co-fermentation of endo- and exo-polygalacturonase overexpression strains resulted in efficient growth on polygalacturonic acid. In the future, the approach will be extended to establish efficient degradation and valorization of pectin.

中文翻译：

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补充乌头草的内在功能，可以降解果胶主链聚半乳糖醛酸。

植物生物量的微生物增值是生物经济中的关键目标。巩固的生物加工的有希望的候选者是双形真菌Ustilago maydis。它含有水解酶以降解生物质成分，并自然产生有价值的次级代谢产物，如衣康酸，苹果酸或糖脂。但是，水解酶主要以菌丝形式表达。在工业发酵过程中应防止这种形态。这些酶的遗传激活可以使相关底物也以酵母形式生长。在这里，对菌株进行了改造，使其可以在聚半乳糖醛酸（果胶的主要成分）上生长。除了激活内在酶以外，还测试了补充异源基因以产生强力酶的作用。非常规分泌途径的存在允许利用真菌和细菌酶。通过最近开发的基于呼吸活动在线确定残留底物的方法，可以评估工程菌株的生长。这样就可以量化整个消耗的底物，将其作为评估酶降解潜力的关键资产，甚至可以评估聚合物底物。内和外聚半乳糖醛酸酶过表达菌株的共同发酵导致在聚半乳糖醛酸上的有效生长。将来，该方法将得到扩展，以建立果胶的有效降解和增值作用。这样就可以量化整个消耗的底物，将其作为评估酶降解潜力的关键资产，甚至可以评估聚合物底物。内和外聚半乳糖醛酸酶过表达菌株的共同发酵导致在聚半乳糖醛酸上的有效生长。将来，该方法将得到扩展，以建立果胶的有效降解和增值作用。这样就可以量化整个消耗的底物，将其作为评估酶降解潜力的关键资产，甚至可以评估聚合物底物。内和外聚半乳糖醛酸酶过表达菌株的共同发酵导致在聚半乳糖醛酸上的有效生长。将来，该方法将得到扩展，以建立果胶的有效降解和增值作用。