Correlational analysis of physicochemical indexes, microbial communities, and volatile components in light-flavor Daqu from north and south regions of China.

Daqu is of great significance to the brewing process of Baijiu, and there are variations in the light-flavor Baijiu Daqu in different regions. However, few studies have been conducted on light-flavor Daqu from the north and south regions of China. In this study, the physicochemical indices, volatile flavor components, and microbial community structure of two types of Daqu from the north and south regions of China were comparatively analyzed. The study findings reveal that Daqu originating from the southern region of China (HB) exhibits superior moisture content, acidity, starch content, and saccharification power. In contrast, Daqu from the northern region of China (SX) displays higher fermentation, esterification, and liquefaction power. The analysis of the microbial community structure revealed that HB was dominated by Bacillus, Kroppenstedtia, Saccharomycopsis, and Thermoascus, while SX was dominated by Bacillus, Prevotella, and Saccharomycopsis. The analysis detected a total of 47 volatile components in both HB Daqu and SX Daqu. The volatile components of pyrazine were significantly more abundant in HB Daqu than in SX Daqu, while alcohol compounds were more prominent in SX Daqu than in HB Daqu. In addition, the RDA analysis established a correlation between dominant microorganisms and volatile components. Cyanobacteria, Fusobacteriota, Ascomycota, Blastocladiomycota, Basidiomycota, and Mucormyce exhibited positive correlations with a significant proportion of the key volatile compounds. This study establishes a scientific foundation for improving the quality of light-flavor Daqu liquor in different regions of China.

The ester production capacity of Pichia kudriavzevii based on functional annotation of genes.

Esters were identified as the primary volatile flavor compounds in Chinese Baijiu, exerting a significant influence on its quality and aroma. This study focused on the yeast strain Pichia kudriavzevii, renowned for its high capacity to produce esters. Whole genome sequences were annotated and analyzed using the GO, KEGG, KOG, CAZy, and Pfam databases to determine the genetic basis underly the enhanced ester production capacity. Results showed that P. kudriavzevii gene function was concentrated in biosynthetic capacity, metabolic capacity, amino acid translocation capacity, glycoside hydrolysis capacity and transfer capacity. Additionally, acyltransferase and kinase were predicted as active sites contributing to P. kudriavzevii high ester production. We further compared the volatile composition differences between P. kudriavzevii and Saccharomyces cerevisiae through Headspace solid-phase microextraction-gas Chromatography-mass spectrometry (HS-SPME-GC-MS), revealing P. kudriavzevii produced 3.5 times more esters than S. cerevisiae. Overall, our findings suggest that P. kudriavzevii had potential applications in the Baijiu brewing industry.

Adding glucose delays the conversion of ethanol and acetic acid to caproic acid in Lacrimispora celerecrescens JSJ-1.

Caproic acid is an important fatty acid with diverse applications. In this study, the biomass growth and metabolites of Lacrimispora celerecrescens JSJ-1 were investigated under different carbon sources (ethanol, starch, sucrose, and glucose), with a focus on the effect of the coexistence of glucose and ethanol on the synthesis of caproic acid. The results showed that starch, glucose, and sucrose all contributed to the biomass of L. celerecrescens JSJ-1. Under the three carbon sources, L. celerecrescens JSJ-1 produced acetic acid, butyric acid, lactic acid, ethanol, and butanol, but caproic acid was not produced. Ethanol was the optimal substrate for the production of caproic acid. When glucose and ethanol coexisted, the generation time of caproic acid was delayed compared with that in ethanol sodium acetate medium (ES medium). This was because glucose was preferentially consumed over ethanol. Lactic acid was generated as a result of glucose consumption, which led to a significant decrease in pH from 6.45 to 4.68. The low pH (< 5) inhibited the synthesis of caproic acid. Then, the strain's usage of lactic acid and the reaction between CaCO3 and lactic acid caused the pH to increase. L. celerecrescens JSJ-1 did not start producing caproic acid using ethanol and acetic acid until the pH increased to 5.8. This research enriches the knowledge regarding the metabolism of L. celerecrescens JSJ-1 and provides guidelines for the industrial production of caproic acid by using L. celerecrescences JSJ-1. KEY POINTS: • Ethanol is the optimal substrate for the synthesis of caproic acid by Lacrimispora celerecrescens JSJ-1. • Lacrimispora celerecrescens JSJ-1 produced lactic acid rapidly when it used glucose, causing a sharp drop in pH. • pH is a crucial factor affecting the synthesis of caproic acid from ethanol by Lacrimispora celerecrescens JSJ-1.

Improving the catalytic characteristics of phenolic acid decarboxylase from Bacillus amyloliquefaciens by the engineering of N-terminus and C-terminus.

BACKGROUND: 4-vinylphenols produced by phenolic acid degradation catalyzed by phenolic acid decarboxylase can be used in food additives as well as flavor and fragrance industry. Improving the catalytic characters of phenolic acid decarboxylase is of great significance to enhance its practical application. RESULTS: A phenolic acid decarboxylase (P-WT) was created from Bacillus amyloliquefaciens ZJH-01. Mutants such as P-C, P-N, P-m1, P-m2, P-Nm1, and P-Nm2 were constructed by site-directed mutagenesis of P-WT. P-C showed better substrate affinities and higher turnover rates than P-WT for p-coumaric acid, ferulic acid, and sinapic acid; however, P-N had reduced affinity toward p-coumaric acid. The extension of the C-terminus increased its acid resistance, whereas the extension of the N-terminus contributed to the alkali resistance and heat resistance. The affinity of P-m1 to four substrates and that of P-m2 to p-coumaric acid and ferulic acid were greatly improved. However, the affinity of P-Nm2 to four phenolic acids was greatly reduced. The residual enzyme activities of P-Nm1 and P-Nm2 considerably improved compared with those of P-m1 and P-m2 after incubation at 50 °C for 60 min. CONCLUSIONS: The extension of the N-terminus may be more conducive to the combination of the binding cavity with the substrate in an alkaline environment and may make its structure more stable.

Bacillus thuringiensis bel protein enhances the toxicity of Cry1Ac protein to Helicoverpa armigera larvae by degrading insect intestinal mucin.

Bacillus thuringiensis has been used as a bioinsecticide to control agricultural insects. Bacillus cereus group genomes were found to have a Bacillus enhancin-like (bel) gene, encoding a peptide with 20 to 30% identity to viral enhancin protein, which can enhance viral infection by degradation of the peritrophic matrix (PM) of the insect midgut. In this study, the bel gene was found to have an activity similar to that of the viral enhancin gene. A bel knockout mutant was constructed by using a plasmid-free B. thuringiensis derivative, BMB171. The 50% lethal concentrations of this mutant plus the cry1Ac insecticidal protein gene were about 5.8-fold higher than those of the BMB171 strain. When purified Bel was mixed with the Cry1Ac protein and fed to Helicoverpa armigera larvae, 3 mug/ml Cry1Ac alone induced 34.2% mortality. Meanwhile, the mortality rate rose to 74.4% when the same amount of Cry1Ac was mixed with 0.8 mug/ml of Bel. Microscopic observation showed a significant disruption detected on the midgut PM of H. armigera larvae after they were fed Bel. In vitro degradation assays showed that Bel digested the intestinal mucin (IIM) of Trichoplusia ni and H. armigera larvae to various degrading products, similar to findings for viral enhancin. These results imply Bel toxicity enhancement depends on the destruction of midgut PM and IIM, similar to the case with viral enhancin. This discovery showed that Bel has the potential to enhance insecticidal activity of B. thuringiensis-based biopesticides and transgenic crops.