Journal of Microbiology

Journal Articles

The human symbiont Bacteroides thetaiotaomicron promotes diet-induced obesity by regulating host lipid metabolism: Sang-Hyun Cho , Yong-Joon Cho , Joo-Hong Park; J. Microbiol. 2022;60(1):118-127. Published online December 29, 2021; DOI: https://doi.org/10.1007/s12275-022-1614-1

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Abstract: The gut microbiome plays an important role in lipid metabolism. Consumption of a high-fat diet (HFD) alters the bacterial communities in the gut, leading to metabolic disorders. Several bacterial species have been associated with diet-induced obesity, nonalcoholic fatty liver disease, and metabolic syndrome. However, the mechanisms underlying the control of lipid metabolism by symbiotic bacteria remain elusive. Here, we show that the human symbiont Bacteroides thetaiotaomicron aggravates metabolic disorders by promoting lipid digestion and absorption. Administration of B. thetaiotaomicron to HFD-fed mice promoted weight gain, elevated fasting glucose levels, and impaired glucose tolerance. Furthermore, B. thetaiotaomicron treatment upregulated the gene expression of the fatty acid transporter and increased fatty acid accumulation in the liver. B. thetaiotaomicron inhibits expression of the gene encoding a lipoprotein lipase inhibitor, angiopoietin-like protein 4 (ANGPTL4), thereby increasing lipase activity in the small intestine. In particular, we found that B. thetaiotaomicron induced the expression of hepcidin, the master regulator of iron metabolism and an antimicrobial peptide, in the liver. Hepcidin treatment resulted in a decrease in ANGPTL4 expression in Caco-2 cells, whereas treatment with an iron chelator restored ANGPTL4 expression in hepcidin- treated cells. These results indicate that B. thetaiotaomicron- mediated regulation of iron storage in intestinal epithelial cells may contribute to increased fat deposition and impaired glucose tolerance in HFD-fed mice.

A study of P release from Fe-P and Ca-P via the organic acids secreted by Aspergillus niger: Da Tian , Liyan Wang , Jun Hu , Liangliang Zhang , Ningning Zhou , Jingjing Xia , Meiyue Xu , Kianpoor Kalkhajeh Yusef , Shimei Wang , Zhen Li , Hongjian Gao; J. Microbiol. 2021;59(9):819-826. Published online August 12, 2021; DOI: https://doi.org/10.1007/s12275-021-1178-5

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Abstract: Phosphate solubilizing fungi (PSF) have been widely applied to dissolve insoluble phosphates (IPs). However, the PSF usually demonstrates a different phosphate solubilizing capacity for various IPs. This study explored the mechanisms of Aspergillus niger for the dissolution of ferric phosphate (FePO4, Fe-P), and tricalcium phosphate (Ca3[PO4]2, Ca-P) regarding the tricarboxylic acid (TCA) cycle. Aspergillus niger has higher phosphorus (P) content released from Ca-P, reached the maximum value of 861 mg/L after seven days of incubation, compared with the 169 mg/L from Fe-P. Oxalic acid promoted the release of P from Ca-P through the formation of calcium oxalate. The presence of Fe-P can stimulate A. niger to secrete large amounts of citric acid, confirmed by the enhancement of citrate synthase (CS) activity. However, citric acid only promotes 0.5% of P released from Fe-P. Meanwhile, although oxalic acid still dominates the release of P from Fe-P, its abundance was significantly declined. In contrast, oxalic acid also shows a higher P release ratio in Ca-P than citric acid, i.e., 36% vs. 22%. This study points to the future usage of A. niger to dissolve IPs in soil required to enhance oxalic acid secretion.

Raman spectroscopy reveals alteration of spore compositions under different nutritional conditions in Lysinibacillus boronitolerans YS11: Youngung Ryu , Minyoung Hong , Soo Bin Kim , Tae Kwon Lee , Woojun Park; J. Microbiol. 2021;59(5):491-499. Published online March 29, 2021; DOI: https://doi.org/10.1007/s12275-021-0679-6

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Abstract: Little is known about final spores components when bacteria undergo sporulation under different nutrient conditions. Different degrees of resistance and germination rates were observed in the three types of spores of Lysinibacillus boronitolerans YS11 (SD, Spores formed in Difco sporulation mediumTM; SC and SF, Spores formed in an agricultural byproduct medium with 10 mM CaCl2 and with 10 mM FeSO4, respectively). Stronger UV resistance was recorded for SF with 1.8–2.3-fold greater survival than SC and SD under UV treatment. The three spore types showed similar heat resistances at 80°C, but survival rates of SC and SD were much higher (~1,000 times) than those of SF at 90°C. However, germination capacity of SF was 20% higher than those of SD and SC on Luria-Bertani agar plates for 24 h. SF germinated more rapidly in a liquid medium with high NaCl concentrations than SC and SD, but became slower under alkaline conditions. Raman spectroscopy was used to analyze the heterogeneities in the three types of vegetative cells and their spores under different nutritional conditions. Exponentially grown-each vegetative cells had different overall Raman peak values. Raman peaks of SC, SD, and SF also showed differences in adenine and amide III compositions and nucleic acid contents. Our data along with Raman spectroscopy provided the evidence that spores formed under under different growth conditions possess very different cellular components, which affected their survival and germination rates.

Functional and structural characterization of Deinococcus radiodurans R1 MazEF toxin-antitoxin system, Dr0416-Dr0417: Immanuel Dhanasingh , Eunsil Choi , Jeongeun Lee , Sung Haeng Lee , Jihwan Hwang; J. Microbiol. 2021;59(2):186-201. Published online February 1, 2021; DOI: https://doi.org/10.1007/s12275-021-0523-z

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Abstract: In prokaryotes, toxin-antitoxin (TA) systems are commonly found. They likely reflect the adaptation of pathogenic bacteria or extremophiles to various unfavorable environments by slowing their growth rate. Genomic analysis of the extremophile Deinococcus radiodurans R1 revealed the presence of eight type II TA systems, including the genes dr0417, dr0660, dr1530, dr0690, and dr1807. Expression of these toxin genes led to inhibition of Escherichia coli growth, whereas their antidote antitoxins were able to recover the growth defect. Remarkably, Dr0417 (DrMazF) showed endoribonuclease activity toward rRNAs as well as mRNAs, as determined by in vivo and in vitro RNA cleavage assays, and this activity was inhibited by Dr0416 (DrMazE). It was also found that the expression of dr0416-0417 module is directly regulated by the DrMazE-MazF complex. Furthermore, this TA module was induced under stress conditions and plays an important role in survival. To understand the regulatory mechanism at the molecular level, we determined the first high-resolution structures of DrMazF alone and of the DrMazE-MazF complex. In contrast with the hetero-hexameric state of typical MazEMazF complexes found in other species, DrMazE-MazF crystal structure consists of a hetero-trimer, with the DNA-binding domain of DrMazE undergoing self-cleavage at the flexible linker loop. Our structure revealed that the unique residue R54 provides an additional positive charge to the substratebinding pocket of DrMazF, its mutation significantly affects the endonuclease activity. Thus, our work reports the unique structural and biochemical features of the DrMazE-MazF system.

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