Dataset Information

Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation.

ABSTRACT:

Background

Consuming red and processed meat has been associated with an increased risk of colorectal cancer (CRC), which is partly attributed to exposure to carcinogens such as heterocyclic amines (HCA) formed during cooking and preservation processes. The interaction of gut microbes and HCA can result in altered bioactivities and it has been shown previously that human gut microbiota can transform mutagenic HCA to a glycerol conjugate with reduced mutagenic potential. However, the major form of HCA in the colon are glucuronides (HCA-G) and it is not known whether these metabolites, via stepwise microbial hydrolysis and acrolein conjugation, are viable precursors for glycerol conjugated metabolites. We hypothesized that such a process could be concurrently catalyzed by bacterial beta-glucuronidase (B-GUS) and glycerol/diol dehydratase (GDH) activity. We therefore investigated how the HCA-G PhIP-N2-?-D-glucuronide (PhIP-G), a representative liver metabolite of PhIP (2-Amino-1-methyl-6-phenylimidazo [4,5-b] pyridine), which is the most abundant carcinogenic HCA in well-cooked meat, is transformed by enzymatic activity of human gut microbial representatives of the phyla Firmicutes, Bacteroidetes, and Proteobacteria.

Results

We employed a combination of growth and enzymatic assays, and a bioanalysis approach combined with metagenomics. B-GUS of Faecalibacterium prausnitzii converted PhIP-G to PhIP and GDH of Flavonifractor plautii, Blautia obeum, Eubacterium hallii, and Lactobacillus reuteri converted PhIP to PhIP-M1 in the presence of glycerol. In addition, B-GUS- and GDH-positive bacteria cooperatively converted PhIP-G to PhIP-M1. A screen of genes encoding B-GUS and GDH was performed for fecal microbiome data from healthy individuals (n?=?103) and from CRC patients (n = 53), which revealed a decrease in abundance of taxa with confirmed GDH and HCA transformation activity in CRC patients.

Conclusions

This study for the first time demonstrates that gut microbes mediate the stepwise transformation of PhIP-G to PhIP-M1 via the intermediate production of PhIP. Findings from this study suggest that targeted manipulation with gut microbes bearing specific functions, or dietary glycerol supplementation might modify gut microbial activity to reduce HCA-induced CRC risk.

SUBMITTER: Zhang J

PROVIDER: S-EPMC6524314 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Publications

Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation.

Zhang Jianbo J Lacroix Christophe C Wortmann Esther E Ruscheweyh Hans-Joachim HJ Sunagawa Shinichi S Sturla Shana J SJ Schwab Clarissa C

BMC microbiology 20190516 1

<h4>Background</h4>Consuming red and processed meat has been associated with an increased risk of colorectal cancer (CRC), which is partly attributed to exposure to carcinogens such as heterocyclic amines (HCA) formed during cooking and preservation processes. The interaction of gut microbes and HCA can result in altered bioactivities and it has been shown previously that human gut microbiota can transform mutagenic HCA to a glycerol conjugate with reduced mutagenic potential. However, the major ...[more]

PMID: 31096909

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Project description:To isolate genes encoding coenzyme B(12)-dependent glycerol and diol dehydratases, metagenomic libraries from three different environmental samples were constructed after allowing growth of the dehydratase-containing microorganisms present for 48 h with glycerol under anaerobic conditions. The libraries were searched for the targeted genes by an activity screen, which was based on complementation of a constructed dehydratase-negative Escherichia coli strain. In this way, two positive E. coli clones out of 560,000 tested clones were obtained. In addition, screening was performed by colony hybridization with dehydratase-specific DNA fragments as probes. The screening of 158,000 E. coli clones by this method yielded five positive clones. Two of the plasmids (pAK6 and pAK8) recovered from the seven positive clones contained genes identical to those encoding the glycerol dehydratase of Citrobacter freundii and were not studied further. The remaining five plasmids (pAK2 to -5 and pAK7) contained two complete and three incomplete dehydratase-encoding gene regions, which were similar to the corresponding regions of enteric bacteria. Three (pAK2, -3, and -7) coded for glycerol dehydratases and two (pAK4 and -5) coded for diol dehydratases. We were able to perform high-level production and purification of three of these dehydratases. The glycerol dehydratases purified from E. coli Bl21/pAK2.1 and E. coli Bl21/pAK7.1 and the complemented hybrid diol dehydratase purified from E. coli Bl21/pAK5.1 were subject to suicide inactivation by glycerol and were cross-reactivated by the reactivation factor (DhaFG) for the glycerol dehydratase of C. freundii. The activities of the three environmentally derived dehydratases and that of glycerol dehydratase of C. freundii with glycerol or 1,2-propanediol as the substrate were inhibited in the presence of the glycerol fermentation product 1,3-propanediol. Taking the catalytic efficiency, stability against inactivation by glycerol, and inhibition by 1,3-propanediol into account, the hybrid diol dehydratase produced by E. coli Bl21/pAK5.1 exhibited the best properties of all tested enzymes for application in the biotechnological production of 1,3-propanediol.

Project description:BackgroundThe direct bioconversion of crude glycerol, a byproduct of biodiesel production, into 1,3-propanediol by microbial fermentation constitutes a remarkably promising value-added applications. However, the low activity of glycerol dehydratase, which is the key and rate-limiting enzyme in the 1,3-propanediol synthetic pathway, caused by crude glycerol impurities is one of the main factors affecting the 1,3-propanediol yield. Hence, the exploration of glycerol dehydratase resources suitable for crude glycerol bioconversion is required for the development of 1,3-propanediol-producing engineered strains.ResultsIn this study, the novel glycerol dehydratase 2eGDHt, which has a tolerance against crude glycerol impurities from Klebsiella pneumoniae 2e, was characterized. The 2eGDHt exhibited the highest activity toward glycerol, with Km and Vm values of 3.42 mM and 58.15 nkat mg-1, respectively. The optimum pH and temperature for 2eGDHt were 7.0 and 37 °C, respectively. 2eGDHt displayed broader pH stability than other reported glycerol dehydratases. Its enzymatic activity was increased by Fe2+ and Tween-20, with 294% and 290% relative activities, respectively. The presence of various concentrations of the crude glycerol impurities, including NaCl, methanol, oleic acid, and linoleic acid, showed limited impact on the 2eGDHt activity. In addition, the enzyme activity was almost unaffected by the presence of an impurity mixture that mimicked the crude glycerol environment. Structural analyses revealed that 2eGDHt possesses more coil structures than reported glycerol dehydratases. Moreover, molecular dynamics simulations and site-directed mutagenesis analyses implied that the existence of unique Val744 from one of the increased coil regions played a key role in the tolerance characteristic by increasing the protein flexibility.ConclusionsThis study provides insight into the mechanism for enzymatic action and the tolerance against crude glycerol impurities, of a novel glycerol dehydratase 2eGDHt, which is a promising glycerol dehydratase candidate for biotechnological conversion of crude glycerol into 1,3-PDO.

Dataset Information

Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation.

Background

Results

Conclusions

Publications

Gut microbial beta-glucuronidase and glycerol/diol dehydratase activity contribute to dietary heterocyclic amine biotransformation.

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