Journal of Microbiology

Volume 59(9); September 2021

Review

[MINIREVIEW]The rapid adaptation of SARS-CoV-2–rise of the variants: transmission and resistance: Sandrine M. Soh , Yeongjun Kim , Chanwoo Kim , Ui Soon Jang , Hye-Ra Lee; J. Microbiol. 2021;59(9):807-818. Published online August 27, 2021; DOI: https://doi.org/10.1007/s12275-021-1348-5

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16 Citations

Abstract: The causative factor of COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is continuously mutating. Interestingly, identified mutations mainly occur in the spike (S) protein which interacts with the ACE2 receptor and is cleaved via serine protease TMPRSS2. Some mutated strains are becoming dominant in various parts of the globe because of increased transmissibility as well as cell entry efficacy. Remarkably, the neutralizing activity of monoclonal antibodies, convalescent sera, and vaccines against the variants has been reported to be significantly reduced. Therefore, the efficacy of various monoclonal antibodies therapy and vaccines against these variants is becoming a great global concern. We herein summarize the current status of SARS-CoV- 2 with gears shifted towards the recent and most common genetic variants in relation to transmission, neutralizing activity, and vaccine efficacy.

Journal Articles

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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23 Citations

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.

Probiotic supplements alleviate gestational diabetes mellitus by restoring the diversity of gut microbiota: a study based on 16S rRNA sequencing: Qing-Xiang Zheng , Xiu-Min Jiang , Hai-Wei Wang , Li Ge , Yu-Ting Lai , Xin-Yong Jiang , Fan Chen , Ping-Ping Huang; J. Microbiol. 2021;59(9):827-839. Published online August 12, 2021; DOI: https://doi.org/10.1007/s12275-021-1094-8

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Abstract: Probiotics effectively prevent and improve metabolic diseases such as diabetes by regulating the intestinal microenvironment and gut microbiota. However, the effects of probiotics in gestational diabetes mellitus are not clear. Here, we showed that probiotic supplements significantly improved fasting blood glucose in a gestational diabetes mellitus rat model. To further understand the mechanisms of probiotics in gestational diabetes mellitus, the gut microbiota were analyzed via 16S rRNA sequencing. We found that compared with the normal pregnant group, the gestational diabetes mellitus rats had decreased diversity of gut microbiota. Moreover, probiotic supplementation restored the diversity of the gut microbiota in gestational diabetes mellitus rats, and the gut microbiota structure tended to be similar to that of normal pregnant rats. In particular, compared with gestational diabetes mellitus rats, the abundance of Firmicutes and Actinobacteria was higher after probiotic supplementation. Furthermore, activating carbohydrate metabolism and membrane transport pathways may be involved in the potential mechanisms by which probiotic supplements alleviate gestational diabetes mellitus. Overall, our results suggested that probiotic supplementation might be a novel approach to restore the gut microbiota of gestational diabetes mellitus rats and provided an experimental evidence for the use of probiotic supplements to treat gestational diabetes melitus.

Characterization of staphylococcal endolysin LysSAP33 possessing untypical domain composition: Jun-Hyeok Yu , Do-Won Park , Jeong-A Lim , Jong-Hyun Park; J. Microbiol. 2021;59(9):840-847. Published online August 12, 2021; DOI: https://doi.org/10.1007/s12275-021-1242-1

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Abstract: Endolysin, a peptidoglycan hydrolase derived from bacteriophage, has been suggested as an alternative antimicrobial agent. Many endolysins on staphylococcal phages have been identified and applied extensively against Staphylococcus spp. Among them, LysK-like endolysin, a well-studied staphylococcal endolysin, accounts for most of the identified endolysins. However, relatively little interest has been paid to LysKunlike endolysin and a few of them has been characterized. An endolysin LysSAP33 encoded on bacteriophage SAP33 shared low homology with LysK-like endolysin in sequence by 41% and domain composition (CHAP-unknown CBD). A green fluorescence assay using a fusion protein for Lys- SAP33_CBD indicated that the CBD domain (157-251 aa) was bound to the peptidoglycan of S. aureus. The deletion of LysSAP33_CBD at the C-terminal region resulted in a significant decrease in lytic activity and efficacy. Compared to LysK-like endolysin, LysSAP33 retained its lytic activity in a broader range of temperature, pH, and NaCl concentrations. In addition, it showed a higher activity against biofilms than LysK-like endolysin. This study could be a helpful tool to develop our understanding of staphylococcal endolysins not belonging to LysK-like endolysins and a potential biocontrol agent against biofilms.

Reversible function of RapA with the C-terminus of RapC in Dictyostelium: Dongju Kim , Wonbum Kim , Taeck Joong Jeon; J. Microbiol. 2021;59(9):853-848.; DOI: https://doi.org/10.1007/s12275-021-1400-5

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Abstract: Rap small GTPases are involved in diverse signaling pathways associated with cell growth, proliferation, and cell migration. There are three Rap proteins in Dictyostelium, RapA, RapB, and RapC. RapA is a key regulator in the control of cell adhesion and migration. Recently RapA and RapC have been reported to have opposite functions in the regulation of cellular processes. In this study, we demonstrate that the C-terminus of RapC, which is not found in RapA, is essential for the opposite functions of RapC and is able to reverse the functions of RapA when fused to the tail of RapA. Cells lacking RapC displayed several defective phenotypes, including spread morphology, strong adhesion, and decreased cell migration compared to wild-type cells. These phenotypes were rescued by full-length RapC, but not by RapC missing the C-terminus. Furthermore, recombinant RapA fused with the C-terminus of RapC completely recovered the phenotypes of rapC null cells, indicating that the functions of RapA were modified to become similar to those of RapC by the C-terminus of RapC with respect to cell morphology, cell adhesion and migration, cytokinesis, and development. These results suggest that the C-terminal residues of RapC are able to suppress and change the functions of other Ras proteins in Ras oncogenic signaling pathways.

Journal Articles

Function of Rhs proteins in porcine extraintestinal pathogenic Escherichia coli PCN033: Wenjia Lu , Jia Tan , Hao Lu , Gaoyan Wang , Wenqi Dong , Chenchen Wang , Xiaodan Li , Chen Tan; J. Microbiol. 2021;59(9):854-860. Published online August 12, 2021; DOI: https://doi.org/10.1007/s12275-021-1189-2

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Abstract: Extraintestinal pathogenic Escherichia coli (ExPEC) is an important zoonotic pathogen that places severe burdens on public health and animal husbandry. There are many pathogenic factors in E. coli. The type VI secretion system (T6SS) is a nano-microbial weapon that can assemble quickly and inject toxic effectors into recipient cells when danger is encountered. T6SSs are encoded in the genomes of approximately 25% of sequenced Gram-negative bacteria. When these bacteria come into contact with eukaryotic cells or prokaryotic microbes, the T6SS assembles and secretes associated effectors. In the porcine ExPEC strain PCN033, we identified four classic rearrangement hotspot (Rhs) genes. We determined the functions of the four Rhs proteins through mutant construction and protein expression. Animal infection experiments showed that the Δrhs-1CT, Δrhs-2CT, Δrhs-3CT, and Δrhs-4CT caused a significant decrease in the multiplication ability of PCN033 in vivo. Cell infection experiments showed that the Rhs protein is involved in anti-phagocytosis activities and bacterial adhesion and invasion abilities. The results of this study demonstrated that rhs1, rhs3, and rh4 plays an important role in the interaction between PCN033 and host cell. Rhs2 has contribution to cell and mice infection. This study helps to elucidate the pathogenic mechanism governing PCN033 and may help to establish a foundation for further research seeking to identify potential T6SS effectors.

Salmonella Typhimurium ST313 isolated in Brazil revealed to be more invasive and inflammatory in murine colon compared to ST19 strains: Amanda Aparecida Seribelli , Tamara R. Machado Ribeiro , Patrick da Silva† , Isabela Mancini Martins , Felipe Pinheiro Vilela , Marta I. Cazentini Medeiros , Kamila Chagas Peronni , Wilson Araújo da Silva Junior , Cristiano Gallina Moreira , Juliana Pfrimer Falcão; J. Microbiol. 2021;59(9):861-870. Published online August 12, 2021; DOI: https://doi.org/10.1007/s12275-021-1082-z

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Abstract: Salmonella Typhimurium (ST313) has caused an epidemic of invasive disease in sub-Saharan Africa and has been recently identified in Brazil. As the virulence of this ST is poorly understood, the present study aimed to (i) perform the RNAseq in vitro of S. Typhimurium STm30 (ST313) grown in Luria-Bertani medium at 37°C; (ii) compare it with the RNAseq of the S. Typhimurium SL1344 (ST19) and S. Typhimurium STm11 (ST19) strains under the same growing conditions; and (iii) examine the colonization capacity and expression of virulence genes and cytokines in murine colon. The STm30 (ST313) strain exhibited stronger virulence and was associated with a more inflammatory profile than the strains SL1344 (ST19) and STm11 (ST19), as demonstrated by transcriptome and in vivo assay. The expression levels of the hilA, sopD2, pipB, and ssaS virulence genes, other Salmonella pathogenicity islands SPI-1 and SPI-2 genes or effectors, and genes of the cytokines IL-1β, IFN-γ, TNF-α, IL-6, IL-17, IL-22, and IL-12 were increased during ST313 infection in C57BL/6J mice. In conclusion, S. Typhimurium STm30 (ST313) isolated from human feces in Brazil express higher levels of pathogenesis- related genes at 37°C and has stronger colonization and invasion capacity in murine colon due to its high expression levels of virulence genes, when compared with the S. Typhimurium SL1344 (ST19) and STm11 (ST19) strains. STm30 (ST313) also induces stronger expression of pro-inflammatory cytokines in this organ, suggesting that it causes more extensive tissue damage.

Screening of small molecules attenuating biofilm formation of Acinetobacter baumannii by inhibition of ompA promoter activity: Seok Hyeon Na , Hyejin Jeon , Man Hwan Oh , Yoo Jeong Kim , Je Chul Lee; J. Microbiol. 2021;59(9):871-878. Published online August 27, 2021; DOI: https://doi.org/10.1007/s12275-021-1394-z

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Abstract: Anti-virulence therapeutic strategies are promising alternatives against drug-resistant pathogens. Outer membrane protein A (OmpA) plays a versatile role in the pathogenesis and antimicrobial resistance of Acinetobacter baumannii. Therefore, OmpA is an innovative target for anti-virulence therapy against A. baumannii. This study aimed to develop a high-throughput screening (HTS) system to discover small molecules inhibiting the ompA promoter activity of A. baumannii and screen chemical compounds using the bacterial growth-based HTS system. The ompA promoter and open reading frame of nptI fusion plasmids that controlled the expression of nptI encoding resistance to kanamycin by the ompA promoter were constructed and then transformed into A. baumannii ATCC 17978. This reporter strain was applied to screen small molecules inhibiting the ompA promoter activity in a chemical library. Of the 7,520 chemical compounds, 15 exhibited ≥ 70% growth inhibition of the report strain cultured in media containing kanamycin. Three compounds inhibited the expression of ompA and OmpA in the outer membrane of A. baumannii ATCC 17978, which subsequently reduced biofilm formation. In conclusion, our reporter strain is useful for large-scale screening of small molecules inhibiting the ompA expression in A. baumannii. Hit compounds identified by the HTS system are promising scaffolds to develop novel therapeutics against A. baumannii.

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