Effect of Exogenous and Endogenous Ectoine on Monascus Development, Metabolism, and Pigment Stability.

Monascus, a key player in fermented food production, is known for generating Monascus pigments (MPs) and monacolin K (MK), possessing bioactive properties. However, the limited stability of MPs and mycotoxin citrinin (CTN) constrain the Monascus industry. Extremolytes like ectoine, derived from bacteria, exhibit cytoprotective potential. Here, we investigated the impact of ectoine on Monascus purpureus ATCC 16365, emphasizing development and secondary metabolism. Exogenous 5 mM ectoine supplementation substantially increased the yields of MPs and MK (105%-150%) and reduced CTN production. Ectoine influenced mycelial growth, spore development, and gene expression in Monascus. Remarkably, ectoine biosynthesis was achieved in Monascus, showing comparable effects to exogenous addition. Notably, endogenous ectoine effectively enhanced the stability of MPs under diverse stress conditions. Our findings propose an innovative strategy for augmenting the production and stability of bioactive compounds while reducing CTN levels, advancing the Monascus industry.

Histone Acetyltransferase Rtt109 Regulates Development, Morphogenesis, and Citrinin Biosynthesis in Monascus purpureus.

Histone acetyltransferase (HAT) has been reported to be pivotal for various physiological processes in many fungi. However, the functions that HAT Rtt109 perform in edible fungi Monascus and the underlying mechanism remains unclear. Here, we identified the rtt109 gene in Monascus, constructed the rtt109 knockout strain (Δrtt109) and its complementary strain (Δrtt109:com) by CRISPR/Cas9 methods, and functionally characterized the roles that Rtt109 play in Monascus. Deletion of rtt109 significantly reduced conidia formation and colony growth, whereas, it increased the yield of Monascus pigments (MPs) and citrinin (CTN). Further real-time quantitative PCR (RT-qPCR) analysis indicated that Rtt109 remarkably affected the transcriptional expression of key genes related to development, morphogenesis, and secondary metabolism of Monascus. Together, our results revealed the critical roles of HAT Rtt109 in Monascus, and enriched our current knowledge of the development and regulation of secondary metabolism in fungi, throwing light on restraining or eliminating citrinin in the development and industrial applications of Monascus.

Syringic Acid Alleviates Dextran Sulfate Sodium-Induced Colitis in Mice by Modulating Gut Microbiota.

Inflammatory bowel disease is known to be associated with alterations in gut microbiota. The bioactive compound syringic acid has been shown to alleviate inflammatory bowel disease, but its interaction with gut microbiota and mechanism of action remain unclear. To address this, we conducted a study in which we investigated the potential benefits of syringic acid in a mouse model of dextran sulfate sodium-induced colitis through gut microbiota modulation. Our results show that oral administration of syringic acid effectively reduced symptoms of colitis, as indicated by reduced disease activity index, and histopathology scores. Moreover, syringic acid administration enriched the abundance of Alistipes and norank_f__norank_o__Gastranaerophilales in mice, suggesting a restoration of impaired gut microbiota. Notably, we found that the effects of syringic acid were similar to those of fecal microbiota transplantation in dextran sulfate sodium-induced mice. Further analysis revealed that syringic acid inhibited the NLRP3-Cas-1-GSDMD-IL-1ß inflammatory vesicle signaling pathway, leading to amelioration of colonic inflammation in a gut microbiota-dependent manner. Our findings demonstrate the potential of syringic acid as a preventive and therapeutic agent for inflammatory bowel disease.

Linoleic acid functions as a quorum-sensing molecule in Monascus purpureus-Saccharomyces cerevisiae co-culture.

When Monascus purpureus was co-cultured with Saccharomyces cerevisiae, we noted significant changes in the secondary metabolism and morphological development of Monascus. In yeast co-culture, although the pH was not different from that of a control, the Monascus mycelial biomass increased during fermentation, and the Monacolin K yield was significantly enhanced (up to 58.87% higher). However, pigment production did not increase. Co-culture with S. cerevisiae significantly increased the expression levels of genes related to Monacolin K production (mokA-mokI), especially mokE, mokF, and mokG. Linoleic acid, that has been implicated in playing a regulating role in the secondary metabolism and morphology of Monascus, was hypothesized to be the effector. Linoleic acid was detected in the co-culture, and its levels changed during fermentation. Addition of linoleic acid increased Monacolin K production and caused similar morphological changes in Monascus spores and mycelia. Exogenous linoleic acid also significantly upregulated the transcription levels of all nine genes involved in the biosynthesis of Monacolin K (up to 69.50% higher), consistent with the enhanced Monacolin K yield. Taken together, our results showed the effect of S. cerevisiae co-culture on M. purpureus and suggested linoleic acid as a specific quorum-sensing molecule in Saccharomyces-Monascus co-culture.

Bacterial communities in home-made Doushen with and without chili pepper.

Doushen is a traditional Chinese fermented soybean product prepared with sterilizated soybeans under open conditions. However, little is known on the bacterial community and their influence on the flavor of Doushen. In the present study, Doushen samples with and without chili pepper were collected to reveal the bacterial community and assess a correlation between bacterial community and VFCs in the two kinds of Doushen samples. We identified four phyla and 97 bacterial genera in the two kinds of Doushen samples. In addition, a total of 17 significantly different OTUs were detected by LEfSe (Line Discriminant Analysis (LDA) Effect Size). Results of Principal coordinates analysis (PCoA), unweighted pair-group method (UPGMA) and functional and phenotypes prediction showed that bacterial communities in the two kinds of Doushen were significantly different. Spearman correlation analysis showed that all the dominant genera, except Clostridium Sensu stricto 1, were significantly correlated with the characteristic VFCs. This study provides a theoretical basis for improving the flavour quality of traditional homemade Doushen.

Histamine Causes Pyroptosis of Liver by Regulating Gut-Liver Axis in Mice.

Huangjiu usually caused rapid-drunkenness and components such as ß-benzyl ethanol (ß-be), isopentanol (Iso), histamine (His), and phenethylamine (PEA) have been reported linked with intoxication. However, the destructive effect of these components on gut microbiota and liver is unclear. In this study, we found oral treatment of these components, especially His, stimulated the level of oxidative stress and inflammatory cytokines in liver and serum of mice. The gut microbiota community was changed and the level of lipopolysaccharide (LPS) increased significantly. Additionally, cellular pyroptosis pathway has been assessed and correlation analysis revealed a possible relationship between gut microbiota and liver pyroptosis. We speculated oral His treatment caused the reprogramming of gut microbiota metabolism, and increased LPS modulated the gut-liver interaction, resulting in liver pyroptosis, which might cause health risks. This study provided a theoretical basis for the effect of Huangjiu, facilitating the development of therapeutic and preventive strategies for related inflammatory disorders.

Effect of γ-Heptalactone on the Morphology and Production of Monascus Pigments and Monacolin K in Monascus purpureus.

Monascus is used widely in Asian countries and produces various biologically active metabolites, such as Monascus pigments (MPs) and monacolin K (MK). In this study, the effect of γ-heptalactone on secondary metabolites and mycelial growth during Monascus purpureus M1 fermentation was investigated. After the addition of 50 µM γ-heptalactone, the yields of MPs (yellow, orange, and red) reached maxima, increased by 115.70, 141.52, and 100.88%, respectively. The 25 µM γ-heptalactone groups showed the highest yield of MK was increased by 62.38% compared with that of the control. Gene expression analysis showed that the relative expression levels of MPs synthesis genes (MpPKS5, MpFasA2, mppB, mppC, mppD, mppG, mpp7, and mppR1/R2) were significantly upregulated after γ-heptalactone treatment. The relative expression levels of MK synthesis genes (mokA, mokC, mokE, mokH, and mokI) were significantly affected. The mycelium samples treated with γ-heptalactone exhibited more folds and swelling than that in the samples of the control group. This study confirmed that the addition of γ-heptalactone has the potential to induce yields of MPs and MK, and promote the expression of biosynthesis genes, which may be related to the transformation of mycelial morphology in M. purpureus.

Variations in Fungal Community and Diversity in Doushen With Different Flavors.

Doushen, a traditional Chinese fermented soybean product, may be spiced or spicy depending on whether pepper powder is added. While numerous studies have investigated the microbial communities of other fermented foods, little is known on the fungal diversity of Doushen. Therefore, in this study, we investigated the fungal community and diversity in both spiced and spicy Doushen. Our results revealed that fungal species richness significantly differed between the samples with different flavors. A total of nine phyla and 188 fungal genera were identified, and Ascomycota and Aspergillus were predominant in all samples. Based on linear discriminant analysis, a total of 57 OTUs were significantly different between the two samples. Results of non-metric multidimensional scaling and unweighted pair-group analysis suggested that the presence of pepper powder affects the microbial community in Doushen. Network analysis showed that microbial interactions between fungal communities in Doushen with different flavors were significantly different. The results on the enumeration and identification of fungi were consistent with the composition of the dominant genera in the samples with different flavors. This study provides a theoretical basis for future research on food ecology in Doushen.

Correction: Microbial diversity in two traditional bacterial douchi from Gansu province in northwest China using Illumina sequencing.

[This corrects the article DOI: 10.1371/journal.pone.0194876.].

Microbial diversity in two traditional bacterial douchi from Gansu province in northwest China using Illumina sequencing.

Douchi has been consumed as a flavoring ingredient for centuries. During production of douchi, numerous microorganisms play important roles in the hydrolysis and conversion of proteins and starch, which are related to the quality and flavor of the end product. Therefore, in the present study, the microbial diversity in two types of home-made traditional bacterial douchi from Gansu province in northwest China was studied by high-throughput sequencing, and a corresponding analysis of the bacterial and fungal communities were conducted. The results showed that geography may have impacted the fungal diversity and the bacterial and fungal species richness in the samples. The results also showed that the microbial community was significantly different in samples of different origin and the difference in the microbial community at the genus level was greater than at phylum level. Two dominant bacterial genera (Bacillus and Ignatzschineria) were common to the two samples, both of which had a relative abundance of more than 1%. Four bacterial genera (Staphylococcus, Aerococcus, Geobacillus, and Jeotgalicoccus) were dominant only in the sample from Qingyang, while another four (Carnobacterium, Proteus, Aneurinibacillus, and Enterococcus) were dominant only in the sample from Longnan. Two dominant fungal genera (Pichia and Candida) were shared by the two samples. Additionally, two genera (Rhodosporidium and Yarrowia) were dominant only in samples from Longnan. The functional genes of the bacteria present in samples indicated that a significant difference was observed in the bacterial community between samples of different origin. We also found that microbial interactions between bacterial and fungal communities in the samples were very complex. This study provides previously unknown information regarding the impact of the environment on microbial communities in douchi and lays a foundation for further investigations into food ecology in bacterial douchi.