Disruption of the Chitin Biosynthetic Pathway Results in Significant Changes in the Cell Growth Phenotypes and Biosynthesis of Secondary Metabolites of Monascus purpureus

Abstract

In this study, the gene monascus-5162 from Monascus purpureus LQ-6, identified as chitin synthase gene VI (chs6), was knocked out to disrupt the chitin biosynthetic pathway and regulate the biosynthesis of Monascus pigments (MPs) and citrinin. The results showed that the aerial hyphae on a solid medium were short and sparse after the deletion of chs6 in M. purpureus LQ-6, significantly reducing the germination percentage of active spores to approximately 22%, but the colony diameter was almost unaffected. Additionally, the deletion of chs6 changed the mycelial morphology of M. purpureus LQ-6 during submerged fermentation and increased its sensitivity to environmental factors. MP and citrinin biosynthesis was dramatically inhibited in the recombinant strain. Furthermore, comparative transcriptome analysis revealed that the pathways related to spore development and growth, including the MAPK signaling pathway, chitin biosynthetic pathway, and regulatory factors LaeA and WetA genes, were significantly downregulated in the early phase of fermentation. The mRNA expression levels of genes in the cluster of secondary metabolites were significantly downregulated, especially those related to citrinin biosynthesis. This is the first detailed study to reveal that chs6 plays a vital role in regulating the cell growth and secondary metabolism of the Monascus genus.

Recent Advances in Chitin Biosynthesis Associated with the Morphology and Secondary Metabolite Synthesis of Filamentous Fungi in Submerged Fermentation

“…In addition, CHS I–III proteins are characterized by hydrophobic C-terminal and hydrophilic N-terminal regions containing a catalytic domain. In our laboratory, the chs protein-encoding gene Monascus_05162, detected in the M. purpureus LQ-6 genome, was identified as a CHS VI class enzyme based on the tertiary structure of the protein and conserved domain analysis [ 57 ].…”

“…Collectively, these findings indicate that CHS V and CHS VII genes are mainly required for normal hyphal growth, perithecia formation, and pathogenicity of filamentous fungi. Moreover, in our previous study, we observed that the deletion of the CHS VI gene in the filamentous fungus M. purpureus induced the development of balloon-tip-like structures in the hyphae, reduced hyphal branching efficiency, promoted hyphal elongation, and altered mycelial pellet formation during submerged fermentation [ 57 ]. Although CHS VI knockout reduced the maximum biomass obtained in submerged fermentation cultures by 19.63%, it did not alter the rate at which the colony diameter of M. purpureus grew [ 57 ].…”

“…Moreover, in our previous study, we observed that the deletion of the CHS VI gene in the filamentous fungus M. purpureus induced the development of balloon-tip-like structures in the hyphae, reduced hyphal branching efficiency, promoted hyphal elongation, and altered mycelial pellet formation during submerged fermentation [ 57 ]. Although CHS VI knockout reduced the maximum biomass obtained in submerged fermentation cultures by 19.63%, it did not alter the rate at which the colony diameter of M. purpureus grew [ 57 ]. In contrast, Cui et al found that the radial growth of Botrytis cinerea colonies substantially reduced as a consequence of disrupting the CHS VI gene, and speculated that this gene is necessary for appropriate hyphal growth [ 55 ].…”

“…Furthermore, these researchers also established that by disrupting chs 4 gene expression, they could regulate the agglomeration of hyphal elements and diameters of P. chrysogenum mycelial pellets during fermentation [ 23 ]. More recently, our research group has been focusing on the morphological changes in M. purpureus during submerged fermentation, and we found that disruption of the biosynthetic pathways of both ergosterol (by deleting the egr 4A and erg 4B genes) and chitin (by knocking out a CHS VI gene) promoted changes in the morphology of the mycelial pellets [ 8 , 57 ].…”

“…To summarize, in the relevant studies conducted on chitin synthase to date, researchers have primarily investigated the relationships between cell wall chitin content and pathogenesis or tolerance, based on the deletion of chs genes [ 54 , 58 , 66 , 73 ], and evaluated the regulatory effect of different members of the chs family on mycelial morphology in submerged fermentation, with the aim of enhancing the yields of target products [ 4 , 57 , 69 , 71 , 72 ]. Based on the findings of these studies, chitin biosynthesis is closely associated with the cell growth and morphology of filamentous fungi, and different members of the chs family play distinct functional roles in this regard.…”