Altered secretion patterns and cell wall organization caused by loss of PodB function in the filamentous fungus Aspergillus nidulans

Karthik R Boppidi,Yan Wang,Liliane Fraga Costa Ribeiro,Mark R Marten,Elizabeth A Richardson,Ranjan Srivastava,Stephen Lincoln,Michelle Momany,Steven D Harris,Sidney M Nelson,Sirasa Iambamrung

doi:10.1038/s41598-018-29615-z

Abstract

Filamentous fungi are widely used in the production of a variety of industrially relevant enzymes and proteins as they have the unique ability to secrete tremendous amounts of proteins. However, the secretory pathways in filamentous fungi are not completely understood. Here, we investigated the role of a mutation in the POlarity Defective (podB) gene on growth, protein secretion, and cell wall organization in Aspergillus nidulans using a temperature sensitive (Ts) mutant. At restrictive temperature, the mutation resulted in lack of biomass accumulation, but led to a significant increase in specific protein productivity. Proteomic analysis of the secretome showed that the relative abundance of 584 (out of 747 identified) proteins was altered due to the mutation. Of these, 517 were secreted at higher levels. Other phenotypic differences observed in the mutant include up-regulation of unfolded protein response (UPR), deformation of Golgi apparatus and uneven cell wall thickness. Furthermore, proteomic analysis of cell wall components in the mutant revealed the presence of intracellular proteins in higher abundance accompanied by lower levels of most cell wall proteins. Taken together, results from this study suggest the importance of PodB as a target when engineering fungal strains for enhanced secretion of valuable biomolecules.

Highlights

Filamentous fungi are widely used as cellular factories in the bioprocess industry for the production of many important products including commodity chemicals, antibiotics, and enzymes[1]
When grown at the restrictive temperature (RT), ASH83 showed isotropic growth and undeveloped germ tubes (Supplementary S1D). This is in contrast to A28 which showed polar growth and fully developed hyphae when it grown at the restrictive temperature (Supplementary Fig. S1B)
PodB was recently shown to be a homolog of COG2, a member of the multi-subunit Conserved Oligomeric Golgi (COG) tethering complex which mediates vesicle trafficking within the Golgi apparatus[15]

Summary

Introduction

Filamentous fungi are widely used as cellular factories in the bioprocess industry for the production of many important products including commodity chemicals, antibiotics, and enzymes[1]. Strategies employed to improve non-fungal protein expression include both biological, i.e., genetic manipulation of host cells[3,4,5,6], and engineering, i.e., modification of bioprocesses[7,8] approaches. While these strategies have led to improvements, titers of non-fungal proteins are often 100-fold lower than those of native fungal proteins[1,9] The reason for this disparity is not clear due to an incomplete understanding of protein secretory mechanisms and associated biological processes in filamentous fungi. We report on the physiological implications and factors related to high protein secretion observed in mutant strain These data collectively suggest that alteration of PodB function might represent a key step in the engineering of fungal strains for increased production of native and non-fungal proteins

Methods

Results

Conclusion