Journal of Microbiology

Journal Articles

Regulator of ribonuclease activity modulates the pathogenicity of Vibrio vulnificus: Jaejin Lee , Eunkyoung Shin , Jaeyeong Park , Minho Lee , Kangseok Lee; J. Microbiol. 2021;59(12):1133-1141. Published online November 9, 2021; DOI: https://doi.org/10.1007/s12275-021-1518-5

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Abstract: RraA, a protein regulator of RNase E activity, plays a unique role in modulating the mRNA abundance in Escherichia coli. The marine pathogenic bacterium Vibrio vulnificus also possesses homologs of RNase E (VvRNase E) and RraA (VvRraA1 and VvRraA2). However, their physiological roles have not yet been investigated. In this study, we demonstrated that VvRraA1 expression levels affect the pathogenicity of V. vulnificus. Compared to the wild-type strain, the VvrraA1-deleted strain (ΔVvrraA1) showed decreased motility, invasiveness, biofilm formation ability as well as virulence in mice; these phenotypic changes of ΔVvrraA1 were restored by the exogenous expression of VvrraA1. Transcriptomic analysis indicated that VvRraA1 expression levels affect the abundance of a large number of mRNA species. Among them, the halflives of mRNA species encoding virulence factors (e.g., smcR and htpG) that have been previously shown to affect VvrraA1 expression-dependent phenotypes were positively correlated with VvrraA1 expression levels. These findings suggest that VvRraA1 modulates the pathogenicity of V. vulnificus by regulating the abundance of a subset of mRNA species.

Ganoderma boninense mycelia for phytochemicals and secondary metabolites with antibacterial activity: Syahriel Abdullah , Se-Eun Jang , Min-Kyu Kwak , KhimPhin Chong; J. Microbiol. 2020;58(12):1054-1064. Published online December 2, 2020; DOI: https://doi.org/10.1007/s12275-020-0208-z

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Abstract: Antiplasmodial nortriterpenes with 3,4-seco-27-norlanostane skeletons, almost entirely obtained from fruiting bodies, represent the main evidential source for bioactive secondary metabolites derived from a relatively unexplored phytopathogenic fungus, Ganoderma boninense. Currently lacking is convincing evidence for antimicrobial secondary metabolites in this pathogen, excluding that obtained from commonly observed phytochemicals in the plants. Herein, we aimed to demonstrate an efficient analytical approach for the production of antibacterial secondary metabolites using the mycelial extract of G. boninense. Three experimental cultures were prepared from fruiting bodies (GBFB), mycelium cultured on potato dextrose agar (PDA) media (GBMA), and liquid broth (GBMB). Through solvent extraction, culture type-dependent phytochemical distributions were diversely exhibited. Water-extracted GBMB produced the highest yield (31.21 ± 0.61%, p < 0.05), but both GBFB and GBMA elicited remarkably higher yields than GBMB when polar-organic solvent extraction was employed. Greater quantities of phytochemicals were also obtained from GBFB and GBMA, in sharp contrast to those gleaned from GBMB. However, the highest antibacterial activity was observed in chloroform-extracted GBMA against all tested bacteria. From liquid-liquid extractions (LLE), it was seen that mycelia extraction with combined chloroform-methanol-water at a ratio of 1:1:1 was superior at detecting antibacterial activities with the most significant quantities of antibacterial compounds. The data demonstrate a novel means of assessing antibacterial compounds with mycelia by LLE which avoids the shortcomings of standardized
method
ologies. Additionally, the antibacterial extract from the mycelia demonstrate that previously unknown bioactive secondary metabolites of the less studied subsets of Ganoderma may serve as active and potent antimicrobial compounds.

Chitosan-chelated zinc modulates cecal microbiota and attenuates inflammatory response in weaned rats challenged with Escherichia coli: Dan Feng , Minyang Zhang , Shiyi Tian , Jing Wang , Weiyun Zhu; J. Microbiol. 2020;58(9):780-792. Published online September 1, 2020; DOI: https://doi.org/10.1007/s12275-020-0056-x

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Abstract: Escherichia coli (E. coli) infection is very common among young growing animals, and zinc supplementation is often used to alleviate inflammation induced by this disease. Therefore, the objective of this study was to evaluate whether chitosan- chelated zinc (CS-Zn) supplementation could attenuate gut injury induced by E. coli challenge and to explore how CSZn modulates cecal microbiota and alleviates intestinal inflammation in weaned rats challenged with E. coli. 36 weaned rats (55.65 ± 2.18 g of BW, n = 12) were divided into three treatment groups consisting of unchallenged rats fed a basal diet (Control) and two groups of rats challenged with E. coli and fed a basal diet or a diet containing 640 mg/kg CS-Zn (E. coli + CS-Zn, containing 50 mg/kg Zn) for a 14-day experiment. On days 10 to 12, each rat was given 4 ml of E. coli solution with a total bacteria count of 1010 CFU by oral gavage daily or normal saline of equal dosage. CS-Zn supplementation mitigated intestinal morphology impairment (e.g. higher crypt depth and lower macroscopic damage index) induced by E. coli challenge (P < 0.05), and alleviated the increase of Myeloperoxidase (MPO) activity after E. coli challenge (P < 0.05). 16S rRNA sequencing analyses revealed that E. coli challenge significantly increased the abundance of Verrucomicrobia and E. coli (P < 0.05). However, CS-Zn supplementation increased the abundance of Lactobacillus and decreased the relative abundance of Proteobacteria, Desulfovibrio and E. coli (P < 0.05). The concentrations of butyrate in the cecal digesta, which decreased due to the challenge, were higher in the E. coli + CS-Zn group (P < 0.05). In addition, CS-Zn supplementation significantly prevented the elevation of pro-inflammatory cytokines IL-6 concentration and upregulated the level of anti-inflammatory cytokines IL-10 in cecal mucosa induced by E. coli infection (P < 0.05). In conclusion, these results indicate that CS-Zn produces beneficial effects in alleviating gut mucosal injury of E. coli challenged rats by enhancing the intestinal morphology and modulating cecal bacterial composition, as well as attenuating inflammatory response.

The putative C2H2 transcription factor RocA is a novel regulator of development and secondary metabolism in Aspergillus nidulans: Dong Chan Won , Yong Jin Kim , Da Hye Kim , Hee-Moon Park , Pil Jae Maeng; J. Microbiol. 2020;58(7):574-587. Published online April 22, 2020; DOI: https://doi.org/10.1007/s12275-020-0083-7

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Abstract: Multiple transcriptional regulators play important roles in the coordination of developmental processes, including asexual and sexual development, and secondary metabolism in the filamentous fungus Aspergillus nidulans. In the present study, we characterized a novel putative C2H2-type transcription factor (TF), RocA, in relation to development and secondary metabolism. Deletion of rocA increased conidiation and caused defective sexual development. In contrast, the overexpression of rocA exerted opposite effects on both phenotypes. Additionally, nullifying rocA resulted in enhanced brlA expression and reduced nsdC expression, whereas its overexpression exerted the opposite effects. These results suggest that RocA functions as a negative regulator of asexual development by repressing the expression of brlA encoding a key asexual development activator, but as a positive regulator of sexual development by enhancing the expression of nsdC encoding a pivotal sexual development activator. Deletion of rocA increased the production of sterigmatocystin (ST), as well as the expression of its biosynthetic genes, aflR and stcU. Additionally, the expression of the biosynthetic genes for penicillin (PN), ipnA and acvA, and for terrequinone (TQ), tdiB and tdiE, was increased by rocA deletion. Thus, it appears that RocA functions as a negative transcriptional modulator of the secondary metabolic genes involved in ST, PN, and TQ biosynthesis. Taken together, we propose that RocA is a novel transcriptional regulator that may act either positively or negatively at multiple target genes necessary for asexual and sexual development and secondary metabolism.

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