Journal of Microbiology

Journal Articles

Ten Novel Species Belonging to the Genus Flavobacterium, Isolated from Freshwater Environments: F. praedii sp. nov., F. marginilacus sp. nov., F. aestivum sp. nov., F. flavigenum sp. nov., F. luteolum sp. nov., F. gelatinilyticum sp. nov., F. aquiphilum sp. nov., F. limnophilum sp. nov., F. lacustre: Hyunyoung Jo , Miri S. Park , Yeonjung Lim , Ilnam Kang , Jang-Cheon Cho; J. Microbiol. 2023;61(5):495-510. Published online May 23, 2023; DOI: https://doi.org/10.1007/s12275-023-00054-4

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Abstract: Eleven bacterial strains were isolated from freshwater environments and identified as Flavobacterium based on 16S rRNA gene sequence analyses. Complete genome sequences of the 11 strains ranged from 3.45 to 5.83 Mb with G + C contents of 33.41–37.31%. The average nucleotide identity (ANI) values showed that strains IMCC34515T and IMCC34518 belonged to the same species, while the other nine strains represented each separate species. The ANI values between the strains and their closest Flavobacterium species exhibited ≤ 91.76%, indicating they represent each novel species. All strains had similar characteristics such as being Gram-stain-negative, rod-shaped, and contained iso-C15:0 as the predominant fatty acid, menaquinone-6 as the respiratory quinone, and phosphatidylethanolamine and aminolipids as major polar lipids. Genomic, phylogenetic, and phenotypic characterization confirmed that the 11 strains were distinct from previously recognized Flavobacterium species. Therefore, Flavobacterium praedii sp. nov. (IMCC34515T = KACC 22282T = NBRC 114937T), Flavobacterium marginilacus sp. nov. (IMCC34673T = KACC 22284T = NBRC 114940T), Flavobacterium aestivum sp. nov. (IMCC34774T = KACC 22285T = NBRC 114941T), Flavobacterium flavigenum sp. nov. (IMCC34775T = KACC22286T = NBRC 114942T), Flavobacterium luteolum sp. nov. (IMCC34776T = KACC 22287T = NBRC 114943T), Flavobacterium gelatinilyticum sp. nov. (IMCC34777T = KACC 22288T = NBRC 114944T), Flavobacterium aquiphilum sp.nov. (IMCC34779T = KACC 22289T = NBRC 114945T), Flavobacterium limnophilum sp. nov. (IMCC36791T = KACC22290T = NBRC 114947T), Flavobacterium lacustre sp. nov. (IMCC36792T = KACC 22291T = NBRC 114948T), and Flavobacterium eburneipallidum sp. nov. (IMCC36793T = KACC 22292T = NBRC 114949T) are proposed as novel species.

Alpha‑Hemolysin from Staphylococcus aureus Obstructs Yeast‑Hyphae Switching and Diminishes Pathogenicity in Candida albicans: Xiaoyu Yu , Yinhe Mao , Guangbo Li , Xianwei Wu , Qiankun Xuan , Simin Yang , Xiaoqing Chen , Qi Cao , Jian Guo , Jinhu Guo , Wenjuan Wu; J. Microbiol. 2023;61(2):233-243. Published online February 9, 2023; DOI: https://doi.org/10.1007/s12275-022-00006-4

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Abstract: The use of antibiotics can disrupt the body’s natural balance and increase the susteptibility of patients towards fungal infections. Candida albicans is a dimorphic opportunistic fungal pathogen with niches similar to those of bacteria. Our aim was to study the interaction between this pathogen and bacteria to facilitate the control of C. albicans infection. Alpha-hemolysin (Hla), a protein secreted from Staphylococcus aureus, causes cell wall damage and impedes the yeast–hyphae transition in C. albicans. Mechanistically, Hla stimulation triggered the formation of reactive oxygen species that damaged the cell wall and mitochondria of C. albicans. The cell cycle was arrested in the G0/G1 phase, CDC42 was downregulated, and Ywp1 was upregulated, disrupting yeast hyphae switching. Subsequently, hyphae development was inhibited. In mouse models, C. albicans pretreated with Hla reduced the C. albicans burden in skin and vaginal mucosal infections, suggesting that S. aureus Hla can inhibit hyphal development and reduce the pathogenicity of candidiasis in vivo.

Expression and purification of intracrine human FGF 11 and study of its FGFR-dependent biological activity: Kyeong Won Lee , Young Jun An , Janet Lee , Ye-Eun Jung , In Young Ko , Jonghwa Jin , Ji Hoon Park , Won Kyu Lee , Kiweon Cha , Sun-Shin Cha , Jung-Hyun Lee , Hyung-Soon Yim; J. Microbiol. 2022;60(11):1086-1094. Published online November 1, 2022; DOI: https://doi.org/10.1007/s12275-022-2406-3

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Abstract: Fibroblast growth factor 11 (FGF11) is one of intracrine FGFs (iFGFs), which function within cells. Unlike canonical FGFs, FGF11 remains intracellularly and plays biological roles in FGF receptor (FGFR)-independent manner. Here, we established an expression system of recombinant FGF11 proteins in E. coli and investigated whether the extracellular administration of FGF11 can activate cellular signaling. Human FGF11 has two isoforms, FGF11a and FGF11b, depending on the presence of nuclear localization sequences (NLSs) in the N-terminus. Because these two isoforms are unstable, we prepared an FGF11a-Mut by substituting three cysteine residues in the NLS with serine and FGF11b-ΔC with C-terminal truncation. The introduction of mutation in the NLS improved the solubility of FGF11 prepared from E. coli. Exogenous addition of FGF11b and FGF11b-ΔC to BALB3T3 increased cell proliferation, while FGF11a-Mut exerted no effect. FGF11b-ΔC showed higher cell proliferation activity and FGFR signaling than FGF11b. The cell-proliferating activities of FGF11b and FGF11b-ΔC were blocked by an FGFR1 inhibitor or a recombinant FGFR1, confirming the FGFR1- dependent extracellular activity of FGF11b. The analysis of circular dichroism suggested that the C-terminus of FGF11 has an α-helical structure, which may affect its interaction with FGFR1. These results suggest that the N-and C-terminus of recombinant FGF11 are involved in the activation of FGFR1. The above results provide novel insights into the function and mechanism of FGF11 that may aid the development of useful ligands for FGFR regulation.

Short-chain fatty acids inhibit the biofilm formation of Streptococcus gordonii through negative regulation of competence-stimulating peptide signaling pathway: Taehwan Park , Jintaek Im , A Reum Kim , Dongwook Lee , Sungho Jeong , Cheol-Heui Yun , Seung Hyun Han; J. Microbiol. 2021;59(12):1142-1149. Published online December 4, 2021; DOI: https://doi.org/10.1007/s12275-021-1576-8

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Abstract: Streptococcus gordonii, a Gram-positive commensal bacterium, is an opportunistic pathogen closely related to initiation and progression of various oral diseases, such as periodontitis and dental caries. Its biofilm formation is linked with the development of such diseases by enhanced resistance against antimicrobial treatment or host immunity. In the present study, we investigated the effect of short-chain fatty acids (SCFAs) on the biofilm formation of S. gordonii. SCFAs, including sodium acetate (NaA), sodium propionate (NaP), and sodium butyrate (NaB), showed an effective inhibitory activity on the biofilm formation of S. gordonii without reduction in bacterial growth. SCFAs suppressed S. gordonii biofilm formation at early time points whereas SCFAs did not affect its preformed biofilm. A quorum-sensing system mediated by competence-stimulating peptide (CSP) is known to regulate biofilm formation of streptococci. Interestingly, SCFAs substantially decreased mRNA expression of comD and comE, which are CSP-sensor and its response regulator responsible for CSP pathway, respectively. Although S. gordonii biofilm formation was enhanced by exogenous synthetic CSP treatment, such effect was not observed in the presence of SCFAs. Collectively, these results suggest that SCFAs have an anti-biofilm activity on S. gordonii through inhibiting comD and comE expression which results in negative regulation of CSP quorum-sensing system. SCFAs could be an effective anti-biofilm agent against S. gordonii for the prevention of oral diseases.

The role of Jacalin-related lectin gene AOL_s00083g511 in the development and pathogenicity of the nematophagous fungus Arthrobotrys oligospora: Xinyuan Dong , Jiali Si , Guanghui Zhang , Zhen Shen , Li Zhang , Kangliang Sheng , Jingmin Wang , Xiaowei Kong , Xiangdong Zha , Yongzhong Wang; J. Microbiol. 2021;59(8):736-745. Published online July 5, 2021; DOI: https://doi.org/10.1007/s12275-021-1029-4

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Abstract: Arthrobotrys oligospora is a model species of nematophagous fungi and has great potential for the biological control of nematode diseases. Lectin is a protein that binds to carbohydrates and their complexes with high specificity, which mediates recognition events in various physiological and pathological processes. This study aimed to investigate the role of the Jacalin-related lectin (JRL) gene, AOL_s00083g511, in A. oligospora development. Through a homology recombination approach, we obtained the AOL_s00083g511 knockout mutant strain (Δg511). Next, the biological characteristics of the Δg511 mutant strain, including growth rate, conidia germination rate, adaptation to environmental stresses, and nematocidal activity, were compared with those of the wild-type (WT) strain. The results showed that the JRL gene AOL_ s00083g511 did not affect fungal growth, conidia germination, 3D-trap formation, and the ability of A. oligospora to prey on nematodes significantly. We speculate that this phenomenon may be caused by a loss of the key β1–β2 loops in the AOL_ s00083g511-encoded JRL domain and an intrinsic genetic compensation of AOL_s00083g511 in this fungus. The growth rates of both strains on high salt or surfactant media were similar; however, in the strong oxidation medium, the growth rate of the Δg511 mutant was significantly lower than that of the WT strain, indicating that AOL_s00083g511 might play a role in oxidative stress resistance. These findings provide a basis for further analysis of the related functions of the JRL gene in A. oligospora and their potential roles in the biological control of nematodes in the future.

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