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- Title
Disruption of <italic>gul</italic>-<italic>1</italic> decreased the culture viscosity and improved protein secretion in the filamentous fungus <italic>Neurospora crassa</italic>.
- Authors
Lin, Liangcai; Sun, Zhiyong; Li, Jingen; Chen, Yong; Liu, Qian; Sun, Wenliang; Tian, Chaoguang
- Abstract
Background: The cellulolytic fungus <italic>Neurospora crassa</italic> is considered a potential host for enzyme and bioethanol production. However, large scale applications are hindered by its filamentous growth. Although previous investigations have shown that mycelial morphology in submerged culture can be controlled by altering physical factors, there is little knowledge available about the potential for morphology control by genetic modification. Results: In this study, we screened morphological mutants in the filamentous fungus <italic>N. crassa</italic>. Of the 90 morphological mutants screened, 14 mutants exhibited considerably higher viscosity compared with that of the wild type strain, and only two mutants showed low-viscosity morphologies in submerged culture. We observed that disruption of <italic>gul</italic>-<italic>1</italic> (NCU01197), which encodes an mRNA binding protein involved in cell wall remodeling, caused pellet formation as the fermentation progressed, and resulted in the most significant decrease in viscosity of culture broth. Moreover, over-expression of <italic>gul</italic>-<italic>1</italic> caused dramatically increased viscosity, suggesting that the <italic>gul</italic>-<italic>1</italic> had an important function in mycelial morphology during submerged cultivation. Transcriptional profiling showed that expression of genes encoding eight GPI-anchored cell wall proteins was lowered in Δ<italic>gul</italic>-<italic>1</italic> while expression of genes associated with two non-anchored cell wall proteins was elevated. Meanwhile, the expression levels of two hydrophobin genes were also significantly altered. These results suggested that GUL-1 affected the transcription of cell wall-related genes, thereby influencing cell wall structure and mycelial morphology. Additionally, the deletion of <italic>gul</italic>-<italic>1</italic> caused increased protein secretion, probably due to a defect in cell wall integrity, suggesting this as an alternative strategy of strain improvement for enzyme production. To confirm practical applications, deletion of <italic>gul</italic>-<italic>1</italic> in the hyper-cellulase producing strain (∆<italic>ncw</italic>-<italic>1</italic>∆<italic>Ncap3m</italic>) significantly reduced the viscosity of culture broth. Conclusions: Using the model filamentous fungus <italic>N. crassa</italic>, genes that affect mycelial morphology in submerged culture were explored through systematic screening of morphological mutants. Disrupting several candidate genes altered viscosities in submerged culture. This work provides an example for controlling fungal morphology in submerged fermentation by genetic engineering, and will be beneficial for industrial fungal strain improvement.
- Subjects
NEUROSPORA crassa; FILAMENTOUS fungi; MICROORGANISM morphology; VISCOSITY; MICROBIAL cultures; MICROBIAL genetic engineering
- Publication
Microbial Cell Factories, 2018, Vol 17, Issue 1, pN.PAG
- ISSN
1475-2859
- Publication type
Article
- DOI
10.1186/s12934-018-0944-5