Biodegradation of phthalate esters by Pantoea dispersa BJQ0007 isolated from Baijiu

A novel and efficient strategy for the biodegradation of di(2-ethylhexyl) phthalate by Fusarium culmorum

Di(2-ethylhexyl) phthalate (DEHP) is a plasticizer that is used worldwide and raises concerns because of its prevalence in the environment and potential toxicity. Herein, the capability of Fusarium culmorum to degrade a high concentration (3 g/L) of DEHP as the sole carbon and energy source in solid-state fermentation (SSF) was studied. Cultures grown on glucose were used as controls. The biodegradation of DEHP by F. culmorum reached 96.9% within 312 h. This fungus produced a 3-fold higher esterase activity in DEHP-supplemented cultures than in control cultures (1288.9 and 443.2 U/L, respectively). In DEHP-supplemented cultures, nine bands with esterase activity (24.6, 31.2, 34.2, 39.5, 42.8, 62.1, 74.5, 134.5, and 214.5 kDa) were observed by zymography, which were different from those in control cultures and from those previously reported for cultures grown in submerged fermentation. This is the first study to report the DEHP biodegradation pathway by a microorganism grown in SSF. The study findings uncovered a novel biodegradation strategy by which high concentrations of DEHP could be biodegraded using two alternative pathways simultaneously. F. culmorum has an outstanding capability to efficiently degrade DEHP by inducing esterase production, representing an ecologically promising alternative for the development of environmental biotechnologies, which might help mitigate the negative impacts of environmental contamination by this phthalate. KEY POINTS: • F. culmorum has potential to tolerate and remove di(2-ethylhexyl) phthalate (DEHP) • Solid-state fermentation is an efficient system for DEHP degradation by F. culmorum • High concentrations of DEHP induce high levels of esterase production by F. culmorum.

Molecular insights into the catabolism of dibutyl phthalate in Pseudomonas aeruginosa PS1 based on biochemical and multi-omics approaches

A comprehensive understanding of the molecular mechanisms underlying microbial catabolism of dibutyl phthalate (DBP) is still lacking. Here, we newly isolated a bacterial strain identified as Pseudomonas aeruginosa PS1 with high efficiency of DBP degradation. The degradation ratios of DBP at 100-1000 mg/L by this strain reached 80-99 % within 72 h without a lag phase. A rare DBP-degradation pathway containing two monobutyl phthalate-catabolism steps was proposed based on intermediates identified by HPLC-TOF-MS/MS. In combination with genomic and transcriptomic analyses, we identified 66 key genes involved in DBP biodegradation and revealed the genetic basis for a new complete catabolic pathway from DBP to Succinyl-CoA or Acetyl-CoA in the genus Pseudomonas for the first time. Notably, we found that a series of homologous genes in Pht and Pca clusters were simultaneously activated under DBP exposure and some key intermediate degradation related gene clusters including Pht, Pca, Xyl, Ben, and Cat exhibited a favorable coexisting pattern, which contributed the high-efficient DBP degradation ability and strong adaptability to this strain. Overall, these results broaden the knowledge of the catabolic diversity of DBP in microorganisms and enhance our understanding of the molecular mechanism underlying DBP biodegradation.

Biodegradation of phthalate acid esters and whole-genome analysis of a novel Streptomyces sp. FZ201 isolated from natural habitats

Di-n-butyl phthalate (DBP) is one of the most extensively used phthalic acid esters (PAEs) and is considered to be an emerging, globally concerning pollutant. The genus Streptomyces holds promise as a degrader of various organic pollutants, but PAE biodegradation mechanisms by Streptomyces species remain unsolved. In this study, a novel PAE-degrading Streptomyces sp. FZ201 isolated from natural habitats efficiently degraded various PAEs. FZ201 had strong resilience against DBP and exhibited immediate degradation, with kinetics adhering to a first-order model. The comprehensive biodegradation of DBP involves de-esterification, β-oxidation, trans-esterification, and aromatic ring cleavage. FZ201 contains numerous catabolic genes that potentially facilitate PAE biodegradation. The DBP metabolic pathway was reconstructed by genome annotation and intermediate identification. Streptomyces species have an open pangenome with substantial genome expansion events during the evolutionary process, enabling extensive genetic diversity and highly plastic genomes within the Streptomyces genus. FZ201 had a diverse array of highly expressed genes associated with the degradation of PAEs, potentially contributing significantly to its adaptive advantage and efficiency of PAE degradation. Thus, FZ201 is a promising candidate for remediating highly PAE-contaminated environments. These findings enhance our preliminary understanding of the molecular mechanisms employed by Streptomyces for the removal of PAEs.

Temporal Profile of the Microbial Community and Volatile Compounds in the Third-Round Fermentation of Sauce-Flavor baijiu in the Beijing Region

Sauce-flavor baijiu produced in the Beijing and Guizhou regions has regional characteristic flavors, but the differences in flavor compounds and reasons for their formation remain unclear. The sauce-flavor baijiu brewing process involves several rounds of fermentation. In this study, we investigated the temporal distribution of microbial communities and flavor substances during the third round of sauce-flavor baijiu fermentation in the Beijing region, and we then compared and analyzed the differences of flavor substances and microorganisms in the fermented grains of sauce-flavor baijiu in the Beijing and Guizhou regions. It was found that 10 bacterial genera and 10 fungal genera were dominant in the fermented grains. The acidity of the fermented grains had a significant driving effect on the microbial community succession. A total of 81 volatile compounds were identified and quantified in the fermented grains, of which esters and alcohols were relatively abundant. The differences in 30 microbial community compositions and their resulting differences in terms of the fermentation parameters of fermented grains are responsible for the differences in the profiles of flavor compounds between sauce-flavor baijiu produced in the Beijing and Guizhou regions.

Complete genome sequence of Acinetobacter indicus and identification of the hydrolases provides direct insights into phthalate ester degradation

A strain designated Acinetobacter indicus WMB-7 with the ability to hydrolyze phthalate esters (PAEs) was isolated from the fermented grains of Baijiu. The genome of the strain was sequenced with a length of 3,256,420 bp and annotated with 3183 genes, of which 36 hydrolases encoding genes were identified. The hydrolases were analyzed by protein structure modeling and molecular docking, and 14 enzymes were docked to the ligand di-butyl phthalate with the catalytic active regions, and showed binding affinity. The 14 enzymes were expressed in E. coli and 5 of them showed the ability for PAEs hydrolysis. Enzyme GK020_RS15665 showed high efficiency for PAEs hydrolysis and could efficiently hydrolyze di-butyl phthalate under an initial concentration of 1000 mg/L with a half-life of 4.24 h. This work combined a series of methods for identifying PAEs hydrolases and offered a molecular basis for PAEs degradation of A. indicus strains from Baijiu.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01334-w.

Insights into the Potential Role of Plasmids in the Versatility of the Genus Pantoea

In the past two decades, 25 different species of the genus Pantoea within the Enterobacteriaceae family, have been isolated from different environmental niches. These species have a wide range of biological roles. Versatility in functions and hosts indicate that this genus has undergone extensive genetic diversification, which can be attributed to the different extra-chromosomal genetic elements or plasmids found across this genus. We have analyzed the functions of these plasmids and categorized them into four major groups for a better understanding of their future applications. The first and second group includes plasmids that contribute to genetic diversification and pathogenicity, respectively. The third group comprises cryptic plasmids of Pantoea. The last group includes plasmids that play a role in the metabolic versatility of the genus Pantoea. We have analyzed the data available up to May 2023 from two databases (viz; NCBI and PLSDB). In our analysis we have found a vast gap in knowledge. Complete gene annotations are available for only a few of the plasmids. This review highlights these challenges as an avenue for future research.

A Novel and Efficient Phthalate Hydrolase from Acinetobacter sp. LUNF3: Molecular Cloning, Characterization and Catalytic Mechanism

Phthalic acid esters (PAEs), which are widespread environmental contaminants, can be efficiently biodegraded, mediated by enzymes such as hydrolases. Despite great advances in the characterization of PAE hydrolases, which are the most important enzymes in the process of PAE degradation, their molecular catalytic mechanism has rarely been systematically investigated. Acinetobacter sp. LUNF3, which was isolated from contaminated soil in this study, demonstrated excellent PAE degradation at 30 °C and pH 5.0-11.0. After sequencing and annotating the complete genome, the gene dphAN1, encoding a novel putative PAE hydrolase, was identified with the conserved motifs catalytic triad (Ser201-Asp295-His325) and oxyanion hole (H127GGG130). DphAN1 can hydrolyze DEP (diethyl phthalate), DBP (dibutyl phthalate) and BBP (benzyl butyl phthalate). The high activity of DphAN1 was observed under a wide range of temperature (10-40 °C) and pH (6.0-9.0). Moreover, the metal ions (Fe2+, Mn2+, Cr2+ and Fe3+) and surfactant TritonX-100 significantly activated DphAN1, indicating a high adaptability and tolerance of DphAN1 to these chemicals. Molecular docking revealed the catalytic triad, oxyanion hole and other residues involved in binding DBP. The mutation of these residues reduced the activity of DphAN1, confirming their interaction with DBP. These results shed light on the catalytic mechanism of DphAN1 and may contribute to protein structural modification to improve catalytic efficiency in environment remediation.

Unveiling the duality of Pantoea dispersa: A mini review

Pantoea dispersa is a Gram-negative bacterium that exists in a variety of environments and has potential in many commercial and agricultural applications, such as biotechnology, environmental protection, soil bioremediation, and plant growth stimulation. However, P. dispersa is also a harmful pathogen to both humans and plants. This "double-edged sword" phenomenon is not uncommon in nature. To ensure survival, microorganisms respond to both environmental and biological stimuli, which could be beneficial or detrimental to other species. Therefore, to harness the full potential of P. dispersa, while minimizing potential harm, it is imperative to unravel its genetic makeup, understand its ecological interactions and underlying mechanisms. This review aims to provide a comprehensive and up-to-date overview of the genetic and biological characteristics of P. dispersa, in addition to potential impacts on plants and humans, as well as to provide insights into potential applications.

Genome mining-guided activation of two silenced tandem genes in Raoultella ornithinolytica XF201 for complete biodegradation of phthalate acid esters

Phthalates (PAEs) are ubiquitous in soils and food products and thus pose a high risk to human health. Herein, genome mining revealed a great diversity of bacteria with PAEs-degrading potential. Mining of the genome of Raoultella ornithinolytica XF201, a novel strain isolated from Dongxiang wild rice rhizosphere, revealed the presence of two silenced tandem genes pcdGH (encoding protocatechuate 3,4-dioxygenase, 3,4-PCD), key aromatic ring-cleaving genes in PAEs biodegradation. Ribosome engineering was successfully utilized to activate the expression of pcdGH genes to produce 3,4-PCD in the mutant XF201-G2U5. The mutant XF201-G2U5 showed high 3,4-PCD activity and could remove 94.5 % of di-n butyl phthalate (DBP) in 72 h. The degradation kinetics obeyed the first-order kinetic model. Strain XF201-G2U5 could also degrade the other PAEs and the main intermediate metabolites, ultimately leading to tricarboxylic acid cycle. Therefore, this strategy facilitates novel bacterial resources discovery for bioremediation of PAEs and other emerging contaminants.

A Thermodynamic and Kinetic Study on Electrochemical Esterification in Aroma-Enhanced Distilled Liquor (Baijiu)

The development of low-alcohol Baijiu is consistent with demand for the industry’s sustainable development. However, the ester aroma of low-alcohol Baijiu is insipid and unstable—mainly due to the hydrolysis of esters during shelf life—thus reducing the industry scale of low-alcohol Baijiu to a significantly small range. An electrochemical method for improving low-alcohol Baijiu’s ester concentration and stability was investigated from the aspects of thermodynamics and kinetics. The key finding is that the new Baijiu’s ester content obtained through distillation is relatively high, exceeding its content in the thermodynamic equilibrium state. Thus, the ester will be hydrolyzed during shelf life. The idea of applying electrochemical catalytic esterification technology to the production of low-alcohol Baijiu in this study is directly derived from the production practice of Baijiu factories; it provides a direction for the further optimization of low-alcohol Baijiu to facilitate the production of an alternative product that will contribute to public health.

Correlational Analysis of the Physicochemical Indexes, Volatile Flavor Components, and Microbial Communities of High-Temperature Daqu in the Northern Region of China

Daqu is a microbial-rich baijiu fermentation starter. The high-temperature Daqu plays an essential role in the manufacturing of sauce-flavored baijiu. However, few studies have focused on three kinds of high-temperature Daqu (white, yellow, and black Daqu) in northern China. In this study, the physicochemical indexes, volatile flavor compounds, and microbial characteristics of the three different colors of high-temperature Daqu in northern China were comparatively analyzed to reveal their potential functions. White Daqu (WQ) exhibited the highest liquefying power and starch, and black Daqu (BQ) showed the highest saccharifying and esterifying powers. A total of 96 volatile components were identified in the three types of Daqu, and the contents of the volatile components of yellow Daqu (YQ) were the highest. The microbial community structure analysis showed that Bacillus and Byssochlamys were dominant in BQ, Kroppenstedtia and Thermoascus were dominant in WQ, and Virgibacillus and Thermomyces dominated the YQ. The RDA analysis revealed the correlation between the dominant microorganisms and different physicochemical indexes. The Spearman correlation analysis indicated that Oceanobacillus, Saccharopolyspora, Staphylococcus, Pseudogracilibacillus, Byssochlamys, and Thermomyces showed positive correlations with part of the majority of the key volatile flavor compounds. This work provides a scientific basis for the actual production of different colors of high-temperature Daqu in the northern region of China for sauce-flavored baijiu.

Recent trends in aroma release and perception during food oral processing: A review

The dynamic and complex peculiarities of the oral environment present several challenges for controlling the aroma release during food consumption. They also pose higher requirements for designing food with better sensory quality. This requires a comprehensive understanding of the basic rules of aroma transmission and aroma perception during food oral processing and its behind mechanism. This review summarized the latest developments in aroma release from food to retronasal cavity, aroma release and delivery influencing factors, aroma perception mechanisms. The individual variance is the most important factor affecting aroma release and perception. Therefore, the intelligent chewing simulator is the key to establish a standard analytical method. The key odorants perceived from the retronasal cavity should be given more attention during food oral processing. Identification of the olfactory receptor activated by specific odorants and its binding mechanisms are still the bottleneck. Electrophysiology and image technology are the new noninvasive technologies in elucidating the brain signals among multisensory, which can fill the gap between aroma perception and other senses. Moreover, it is necessary to develop a new approach to integrate the relationship among aroma binding parameters, aroma concentration, aroma attributes and cross-modal reactions to make the aroma prediction model more accurate.

Clostridium btbubcensis BJN0001, a potentially new species isolated from the cellar mud of Chinese strong-flavor baijiu, produces ethanol, acetic acid and butyric acid from glucose

A novel strain, designated BJN0001, was isolated from the cellar mud of Chinese strong-flavor baijiu. The complete genome of strain BJN0001 was 2,688,791 bp and annotated with 2610 genes. Whole-genome similarity metrics such as average nucleotide identity (ANI) of BJN0001 with reference genomes reveals clear species boundaries of < 95% ANI value for species. The DNA-DNA hybridization (DDH) values of BJN0001 with the type species were all lower than 70% DDH value for species. Based on these results, the strain BJN0001 was considered a potentially new species of the genus Clostridium. Meanwhile, the fermentation characteristics indicated that the strain had the capability to convert glucose to ethanol, acetic acid and butyric acid, which could provide basic data for revealing its function in baijiu fermentation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03271-7.

Adsorption of Phthalate Acid Esters by Activated Carbon: The Overlooked Role of the Ethanol Content

Ethanol has great effects on the adsorption of phthalate acid esters (PAEs) on activated carbon (AC), which are usually overlooked and hardly studied. This study investigated the overlooked effects of ethanol on the adsorption of PAEs in alcoholic solutions. The adsorption capacities of dibutyl phthalate (DBP) on AC in solutions with ethanol contents of 30, 50, 70, and 100 v% were only 59%, 43%, 19%, and 10% of that (16.39 mg/g) in water, respectively. The ethanol content increase from 50 v% to 100 v% worsened the adsorption performances significantly with the formation of water–ethanol–DBP clusters (decreasing from 13.99 mg/g to 2.34 mg/g). The molecular dynamics simulation showed that the DBP tended to be distributed farther away from the AC when the ethanol content increased from 0 v% to 100 v% (the average distribution distance increased from 5.25 Å to 15.3 Å). The PAEs with shorter chains were more affected by the presence of ethanol than those with longer chains. Taking DBP as an example, the adsorption capacity of AC in ethanol (0.41 mg/g) is only 2.2% of that in water (18.21 mg/g). The application results in actual Baijiu samples showed that the adsorption of PAEs on AC had important effects on the Baijiu flavors.

Characterization of an Aspergillus niger for Efficient Fatty Acid Ethyl Ester Synthesis in Aqueous Phase and the Molecular Mechanism

Fatty acid ethyl esters are important flavor chemicals in strong-flavor baijiu. Microorganisms are the main contributors to ester synthesis during baijiu manufacture. However, the ester synthesis was unstable between batches. This was owing to a limited knowledge of the mechanisms for ester synthesis by microorganisms. In this work, a fatty acid ethyl ester synthesizing Aspergillus niger strain CGMCC (China General Microbiological Culture Collection) 3.4309 was identified. The conversion ratios of ethyl valerate, ethyl caproate, ethyl caprylate, and ethyl caprate were 7.87, 29.20, 94.80, and 85.20%, respectively, under the optimized conditions. A comparison of transcriptomes under the initial and optimized ester synthetic conditions indicated that 23 genes were upregulated in transcription level and encoded enzymes with potential abilities for ester synthesis. Eleven of the enzymes were expressed, and three of them, numbered An605, An1097, and An3131, showed the ability to catalyze fatty acid ethyl ester synthesis under aqueous phase, with capric acid as the preferred substrate. The possible enzymatic catalytic mechanism was proposed based on homology modeling and molecular docking. This study reported for the first time that A. niger showed the ability to efficiently catalyze the synthesis of short- and medium-chain fatty acid ethyl esters in aqueous phase, identified the key enzymes, and analyzed the basic enzymatic properties. This is helpful to promote the application of related microorganisms and enzyme resources in the baijiu industry.

Correlation between microbial communities and flavor compounds during the fifth and sixth rounds of sauce-flavor baijiu fermentation

Sauce-flavor baijiu is a representative of Chinese traditional fermented baijiu using grains as the raw materials through the co-fermentation of microorganisms. The whole manufacturing process includes 7 times of distillation and generates 7 kinds of base baijius. The final product is a mixture of the 7 kinds of base baijius. Thus the base baijius greatly affect the quality of the final product. The quality of the base baijiu obtained by the sixth distillation is obviously poorer than that of the fifth one. However, the reason is still unclear and limits the quality control of baijiu fermentation. In this study, the flavor substances and microbiota in the up, middle and bottom layers of fermented grains in the fifth and sixth rounds were compared. Some flavor esters showed obviously decreased concentrations in the sixth round, including ethyl benzoneacetic acid, ethyl hexanoic acid, ethyl dodecanoic acid, diethyl butanedioic acid, and ethyl 2-hydroxyl-propanoic acid. Meanwhile, an off-flavor p-cresol was detected in the sixth round. Correlation analysis of flavor chemicals and microbiota indicated that fungi in the fifth round played an important role for ester synthesis. Some bacterial and fungal species were both positively correlated with p-cresol synthesis, and the related p-cresol metabolic pathways were proposed for the first time. These results revealed flavor divergences of fermented grains between the fifth and sixth rounds, and will ultimately help to improve baijiu quality.