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

Functional analysis of basidiomycete specific chitin synthase genes in the agaricomycete fungus Pleurotus ostreatus

Chitin is an essential structural component of fungal cell walls composed of transmembrane proteins called chitin synthases (CHSs), which have a large range of reported effects in ascomycetes; however, are poorly understood in agaricomycetes. In this study, evolutionary and molecular genetic analyses of chs genes were conducted using genomic information from nine ascomycete and six basidiomycete species. The results support the existence of seven previously classified chs clades and the discovery of three novel basidiomycete-specific clades (BI-BIII). The agaricomycete fungus Pleurotus ostreatus was observed to have nine putative chs genes, four of which were basidiomycete-specific. Three of these basidiomycete specific genes were disrupted in the P. ostreatus 20b strain (ku80 disruptant) through homologous recombination and transformants were obtained (Δchsb2, Δchsb3, and Δchsb4). Despite numerous transformations Δchsb1 was unobtainable, suggesting disruption of this gene causes a crucial negative effect in P. ostreatus. Disruption of these chsb2-4 genes caused sparser mycelia with rougher surfaces and shorter aerial hyphae. They also caused increased sensitivity to cell wall and membrane stress, thinner cell walls, and overexpression of other chitin and glucan synthases. These genes have distinct roles in the structural formation of aerial hyphae and cell walls, which are important for understanding basidiomycete evolution in filamentous fungi.

Enhanced extracellular production of laccase in Coprinopsis cinerea by silencing chitinase gene

Laccase, a copper-containing polyphenol oxidase, is an important green biocatalyst. In this study, Laccase Lcc5 was homologous recombinantly expressed in Coprinopsis cinerea and a novel strategy of silencing chitinase gene expression was used to enhance recombinant Lcc5 extracellular yield. Two critical chitinase genes, ChiEn1 and ChiE2, were selected by analyzing the transcriptome data of C. cinerea FA2222, and their silent expression was performed by RNA interference (RNAi). It was found that silencing either ChiEn1 or ChiE2 reduced sporulation and growth rate, and increased cell wall sensitivity, but had no significant effect on mycelial branching. Among them, the extracellular laccase activity of the ChiE2-silenced engineered strain Cclcc5-antiChiE2-5 and the control Cclcc5-13 reached the highest values (38.2 and 25.5 U/mL, respectively) at 250 and 150 rpm agitation speeds, corresponding to productivity of 0.35 and 0.19 U/mL·h, respectively, in a 3-L fermenter culture. Moreover, since Cclcc5-antiChiE2-5 could withstand greater shear forces, its extracellular laccase activity was 2.6-fold higher than that of Cclcc5-13 when the agitation speed was all at 250 rpm. To our knowledge, this is the first report of enhanced recombinant laccase production in C. cinerea by silencing the chitinase gene. This study will pave the way for laccase industrial production and accelerate the development of a C. cinerea high-expression system. KEY POINTS: • ChiEn1 and ChiE2 are critical chitinase genes in C. cinerea FA2222 genome. • Chitinase gene silencing enhanced the tolerance of C. cinerea to shear forces. • High homologous production of Lcc5 is achieved by fermentation in a 3-L fermenter.

The effects of environmental factors on the synthesis of water-soluble Monascus red pigments via submerged fermentation: a review

Monascus pigments (MPs) have been used as natural food pigments for many years. There is a high demand for Monascus red pigments (MRPs) to enhance color and for antibacterial and cancer prevention therapies in food and medicine. Most MRPs are not water soluble, and the yield of water-soluble MRPs is naturally low. On the other hand, water-soluble MRP is more cost effective for application in industrial mass production. Therefore, it is important to improve the yield of water-soluble MRPs. Environmental factors have a significant influence on the synthesis of water-soluble MRPs, which is crucial for the development of industrial production of water-soluble MRPs. This review introduces the biosynthetic pathways of water-soluble MRPs and summarizes the effects of environmental factors on the yield of water-soluble MRPs. Acetyl coenzyme A (acetyl-CoA) is a precursor for MPs synthesis. Carbon and nitrogen sources and the carbon/nitrogen ratio can impact MP production by regulating the metabolic pathway of acetyl-CoA. Optimization of fermentation conditions to change the morphology of Monascus can stimulate the synthesis of MPs. The appropriate choice of nitrogen sources and pH values can promote the synthesis of MRPs from MPs. Additives such as metal ions and non-ionic surfactants can affect the fluidity of Monascus cell membrane and promote the transformation of MRPs into water-soluble MRPs. This review will lay the foundation for the industrial production of water-soluble MRPs. © 2024 Society of Chemical Industry.

Synergism with Shikimic Acid Restores β-Lactam Antibiotic Activity against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has evolved into a dangerous pathogen resistant to beta-lactam antibiotics (BLAs) and has become a worrisome superbug. In this study, a strategy in which shikimic acid (SA), which has anti-inflammatory and antibacterial activity, is combined with BLAs to restart BLA activity was proposed for MRSA treatment. The synergistic effects of oxacillin combined with SA against oxacillin resistance in vitro and in vivo were investigated. The excellent synergistic effect of the oxacillin and SA combination was confirmed by performing the checkerboard assay, time-killing assay, live/dead bacterial cell viability assay, and assessing protein leakage. SEM showed that the cells in the control group had a regular, smooth, and intact surface. In contrast, oxacillin and SA or the combination treatment group exhibited different degrees of surface collapse. q-PCR indicated that the combination treatment group significantly inhibited the expression of the mecA gene. In vivo, we showed that the combination treatment increased the survival rate and decreased the bacterial load in mice. These results suggest that the combination of oxacillin with SA is considered an effective treatment option for MRSA, and the combination of SA with oxacillin in the treatment of MRSA is a novel strategy.

Disruption of UDP-galactopyranose mutase expression: A novel strategy for regulation of galactomannan biosynthesis and monascus pigments secretion in Monascus purpureus M9

The impact of the cell wall structure of Monascus purpureus M9 on the secretion of extracellular monascus pigments (exMPs) was investigated. To modify the cell wall structure, UDP-galactopyranose mutase (GlfA) was knocked out using Agrobacterium-mediated transformation method, leading to a significant reduction in the Galf-based polysaccharide within the cell wall. Changes in mycelium morphology, sporogenesis, and the expression of relevant genes in M9 were also observed following the mutation. Regarding MPs secretion, a notable increase was observed in six types of exMPs (R1, R2, Y1, Y2, O1 and O2). Specifically, these exMPs exhibited enhancement of 1.33, 1.59, 0.8, 2.45, 2.89 and 4.03 times, respectively, compared to the wild-type strain. These findings suggest that the alteration of the cell wall structure could selectively influence the secretion of MPs in M9. The underlying mechanisms were also discussed. This research contributes new insights into the regulation of the synthesis and secretion of MPs in Monascus spp..

Integrated transcriptomic and metabolomic analyses reveal the toxic effects of dimethoate on green vegetable soya bean seedlings

The insecticide dimethoate, an organophosphate, has been used on crops, soybeans, fruits, and vegetables since the 1960s and is considered one of the most widely used pesticides. However, the understanding of the molecular mechanisms of dimethoate in crops, especially crop seedlings, is still limited. The green vegetable soya bean (Glycine max merr) is usually used as a vegetable-like fruit of soybean in many Asian countries. This study aimed to analyze the effect of dimethoate on the growth of green vegetable soya bean seedlings at the metabolic and transcriptional levels. An integrated analysis of the transcriptome and metabolome was performed to determine the responses of green vegetable soya bean seedlings to different concentrations (D1 for low dose, D2 for high dose and C for control) of dimethoate. In omics analyses, 4156 differentially expressed genes (DEGs) and 1935 differentially abundant metabolites (DAMs) were identified in the D1/C comparison, and 11,162 DEGs and 819 DAMs were identified in D2/C. Correlation analyses revealed dimethoate affected the metabolic pathways of green vegetable soya beans such as the biosynthesis of secondary metabolites and microbial metabolism in diverse environmental pathways, demonstrating that even small doses of dimethoate can affect green vegetable soya bean seedlings in a short period of time. Our study further enriches our understanding of the molecular mechanisms by which green vegetable soya beans are treated with dimethoate and provides a deeper understanding of the effects of dimethoate on crops.

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

Metabolites produced by filamentous fungi are used extensively in the food and drug industries. With the development of the morphological engineering of filamentous fungi, numerous biotechnologies have been applied to alter the morphology of fungal mycelia and enhance the yields and productivity of target metabolites during submerged fermentation. Disruption of chitin biosynthesis can modify the cell growth and mycelial morphology of filamentous fungi and regulate the biosynthesis of metabolites during submerged fermentation. In this review, we present a comprehensive coverage of the categories and structures of the enzyme chitin synthase, chitin biosynthetic pathways, and the association between chitin biosynthesis and cell growth and metabolism in filamentous fungi. Through this review, we hope to increase awareness of the metabolic engineering of filamentous fungal morphology, provide insights into the molecular mechanisms of morphological control via chitin biosynthesis, and describe strategies for the application of morphological engineering to enhance the production of target metabolites in filamentous fungi during submerged fermentation.