Abstract
Using a gnotobiotic mouse model, we previously observed the upregulation of 2-deoxy-D-gluconate 3-dehydrogenase (KduD) in intestinal E. coli of mice fed a lactose-rich diet and the downregulation of this enzyme and of 5-keto 4-deoxyuronate isomerase (KduI) on a casein-rich diet. The present study aimed to define the role of the so far poorly characterized E. coli proteins KduD and KduI in vitro. Galacturonate and glucuronate induced kduD and kduI gene expression 3-fold and 7 to 11-fold, respectively, under aerobic conditions as well as 9 to 20-fold and 19 to 54-fold, respectively, under anaerobic conditions. KduI facilitated the breakdown of these hexuronates. In E. coli, galacturonate and glucuronate are normally degraded by UxaABC and UxuAB. However, osmotic stress represses the expression of the corresponding genes in an OxyR-dependent manner. When grown in the presence of galacturonate or glucuronate, kduID-deficient E. coli had a 30% to 80% lower maximal cell density and 1.5 to 2-fold longer doubling times under osmotic stress conditions than wild type E. coli. Growth on lactose promoted the intracellular formation of hexuronates, which possibly explain the induction of KduD on a lactose-rich diet. These results indicate a novel function of KduI and KduD in E. coli and demonstrate the crucial influence of osmotic stress on the gene expression of hexuronate degrading enzymes.
Highlights
The intestinal tract harbors a complex microbial community, whose composition is modulated by nutrition [1,2,3]
Using a gnotobiotic mouse model, we previously demonstrated that intestinal Escherichia coli K-12 (MG1655) modulates its metabolism in response to various diets [7]
In a previously reported experiment, three groups of gnotobiotic C3H mice monoassociated with E. coli K-12 (MG1655) were fed a diet rich in starch, lactose, or casein for 3 weeks (Figure S1 in the supplementary material) [7] and the proteomes of E. coli obtained from mice fed the latter diets were compared with those of mice fed the starch diet
Summary
The intestinal tract harbors a complex microbial community, whose composition is modulated by nutrition [1,2,3]. Microbiome analysis revealed an increase in genes encoding bacterial enzymes involved in amino acid degradation, carbohydrate catabolism, vitamin biosynthesis, and bile salt metabolism in response to a protein-rich host diet [6]. The key finding in this study was the upregulation of OxyRdependent proteins in intestinal E. coli from mice fed a lactose-rich diet and their essential role in bacterial adaptation to lactosemediated osmotic stress [7]. We observed the dietdependent expression of two E. coli proteins that have been identified [8,9,10] but whose roles in the E. coli metabolism are still obscure: namely, the 2-deoxy-D-gluconate 3-dehydrogenase (KduD), which was 2.4-fold upregulated in E. coli of mice on the lactose diet and 4.0-fold downregulated in E. coli of mice on the casein diet (both versus control [starch] diet), and the 5-keto 4deoxyuronate isomerase (KduI), which was 8.3-fold lower in E. coli of mice fed the casein diet [7]. The results obtained indicate that KduI and KduD play a crucial role in the conversion of hexuronates in E. coli under osmotic stress conditions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
