Journal of Microbiology

Review

Role of Rab GTPases in Bacteria Escaping from Vesicle Trafficking of Host Cells.: Huiling Xu, Shengnan Wang, Xiaozhou Wang, Pu Zhang, Qi Zheng, ChangXi Qi, Xiaoting Liu, Muzi Li, Yongxia Liu, Jianzhu Liu; J. Microbiol. 2024;62(8):581-590. Published online August 30, 2024; DOI: https://doi.org/10.1007/s12275-024-00162-9

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Abstract: Most bacteria will use their toxins to interact with the host cell, causing damage to the cell and then escaping from it. When bacteria enter the cell, they will be transported via the endosomal pathway. Rab GTPases are involved in bacterial transport as major components of endosomes that bind to their downstream effector proteins. The bacteria manipulate some Rab GTPases, escape the cell, and get to survive. In this review, we will focus on summarizing the many processes of how bacteria manipulate Rab GTPases to control their escape.

Journal Article

Cultivation of Diverse Novel Marine Bacteria from Deep Ocean Sediment Using Spent Culture Supernatant of Ca. Bathyarchaeia Enrichment.: Sidra Erum Ishaq, Tariq Ahmad, Lewen Liang, Ruize Xie, Tiantian Yu, Yinzhao Wang, Fengping Wang; J. Microbiol. 2024;62(8):611-625. Published online July 10, 2024; DOI: https://doi.org/10.1007/s12275-024-00145-w

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Abstract: Most microorganisms resist pure cultivation under conventional laboratory conditions. One of the primary issues for this un-culturability is the absence of biologically produced growth-promoting factors in traditionally defined growth media. However, whether cultivating microbes by providing spent culture supernatant of pivotal microbes in the growth medium can be an effective approach to overcome this limitation is still an under-explored area of research. Here, we used the spent culture medium (SCM) method to isolate previously uncultivated marine bacteria and compared the efficiency of this method with the traditional cultivation (TC) method. In the SCM method, Ca. Bathyarchaeia-enriched supernatant (10%) was used along with recalcitrant organic substrates such as lignin, humic acid, and organic carbon mixture. Ca. Bathyarchaeia, a ubiquitous class of archaea, have the capacity to produce metabolites, making their spent culture supernatant a key source to recover new bacterial stains. Both cultivation methods resulted in the recovery of bacterial species from the phyla Pseudomonadota, Bacteroidota, Actinomycetota, and Bacillota. However, our SCM approach also led to the recovery of species from rarely cultivated groups, such as Planctomycetota, Deinococcota, and Balneolota. In terms of the isolation of new taxa, the SCM method resulted in the cultivation of 80 potential new strains, including one at the family, 16 at the genus, and 63 at the species level, with a novelty ratio of ~ 35% (80/219). In contrast, the TC method allowed the isolation of ~ 10% (19/171) novel strains at species level only. These findings suggest that the SCM approach improved the cultivation of novel and diverse bacteria.

Review

The Role of Extracellular Vesicles in Pandemic Viral Infections.: Woosung Shim, Anjae Lee, Jung-Hyun Lee; J. Microbiol. 2024;62(6):419-427. Published online June 25, 2024; DOI: https://doi.org/10.1007/s12275-024-00144-x

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Abstract: Extracellular vesicles (EVs), of diverse origin and content, are membranous structures secreted by a broad range of cell types. Recent advances in molecular biology have highlighted the pivotal role of EVs in mediating intercellular communication, facilitated by their ability to transport a diverse range of biomolecules, including proteins, lipids, DNA, RNA and metabolites. A striking feature of EVs is their ability to exert dual effects during viral infections, involving both proviral and antiviral effects. This review explores the dual roles of EVs, particularly in the context of pandemic viruses such as HIV-1 and SARS-CoV-2. On the one hand, EVs can enhance viral replication and exacerbate pathogenesis by transferring viral components to susceptible cells. On the other hand, they have intrinsic antiviral properties, including activation of immune responses and direct inhibition of viral infection. By exploring these contrasting functions, our review emphasizes the complexity of EV-mediated interactions in viral pathogenesis and highlights their potential as targets for therapeutic intervention. The insights obtained from investigating EVs in the context of HIV-1 and SARS-CoV-2 provide a deeper understanding of viral mechanisms and pathologies, and offer a new perspective on managing and mitigating the impact of these global health challenges.

Journal Article

Tubulysin Production by the Dead Cells of Archangium gephyra KYC5002.: Seohui Park, Chaehyeon Park, Yujin Ka, Kyungyun Cho; J. Microbiol. 2024;62(6):463-471. Published online June 13, 2024; DOI: https://doi.org/10.1007/s12275-024-00130-3

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Abstract: Archangium gephyra KYC5002 produces tubulysins during the death phase. In this study, we aimed to determine whether dead cells produce tubulysins. Cells were cultured for three days until the verge of the death phase, disrupted via ultrasonication, incubated for 2 h, and examined for tubulysin production. Non-disrupted cells produced 0.14 mg/L of tubulysin A and 0.11 mg/L of tubulysin B. Notably, tubulysin A production was increased by 4.4-fold to 0.62 mg/L and that of tubulysin B was increased by 6.7-fold to 0.74 mg/L in the disrupted cells. The same increase in tubulysin production was observed when the cells were killed by adding hydrogen peroxide. However, when the enzymes were inactivated via heat treatment of the cultures at 65 °C for 30 min, no significant increase in tubulysin production due to cell death was observed. Reverse transcription-quantitative polymerase chain reaction analysis of tubB mRNA revealed that the expression levels of tubulysin biosynthetic enzyme genes increased during the death phase compared to those during the vegetative growth phase. Our findings suggest that A. gephyra produces biosynthetic enzymes and subsequently uses them for tubulysin production in the cell death phase or during cell lysis by predators.

Review

Structural Insights into the Lipopolysaccharide Transport (Lpt) System as a Novel Antibiotic Target.: Yurim Yoon, Saemee Song; J. Microbiol. 2024;62(4):261-275. Published online May 31, 2024; DOI: https://doi.org/10.1007/s12275-024-00137-w

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Abstract: Lipopolysaccharide (LPS) is a critical component of the extracellular leaflet within the bacterial outer membrane, forming an effective physical barrier against environmental threats in Gram-negative bacteria. After LPS is synthesized and matured in the bacterial cytoplasm and the inner membrane (IM), LPS is inserted into the outer membrane (OM) through the ATP-driven LPS transport (Lpt) pathway, which is an energy-intensive process. A trans-envelope complex that contains seven Lpt proteins (LptA-LptG) is crucial for extracting LPS from the IM and transporting it across the periplasm to the OM. The last step in LPS transport involves the mediation of the LptDE complex, facilitating the insertion of LPS into the outer leaflet of the OM. As the Lpt system plays an essential role in maintaining the impermeability of the OM via LPS decoration, the interactions between these interconnected subunits, which are meticulously regulated, may be potential targets for the development of new antibiotics to combat multidrug-resistant Gram-negative bacteria. In this review, we aimed to provide an overview of current research concerning the structural interactions within the Lpt system and their implications to clarify the function and regulation of LPS transport in the overall process of OM biogenesis. Additionally, we explored studies on the development of therapeutic inhibitors of LPS transport, the factors that limit success, and future prospects.

Journal Article

Autotrophy to Heterotrophy: Shift in Bacterial Functions During the Melt Season in Antarctic Cryoconite Holes.: Aritri Sanyal, Runa Antony, Gautami Samui, Meloth Thamban; J. Microbiol. 2024;62(8):591-609. Published online May 30, 2024; DOI: https://doi.org/10.1007/s12275-024-00140-1

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2 Citations

Abstract: Microbes residing in cryoconite holes (debris, water, and nutrient-rich ecosystems) on the glacier surface actively participate in carbon and nutrient cycling. Not much is known about how these communities and their functions change during the summer melt-season when intense ablation and runoff alter the influx and outflux of nutrients and microbes. Here, we use high-throughput-amplicon sequencing, predictive metabolic tools and Phenotype MicroArray techniques to track changes in bacterial communities and functions in cryoconite holes in a coastal Antarctic site and the surrounding fjord, during the summer season. The bacterial diversity in cryoconite hole meltwater was predominantly composed of heterotrophs (Proteobacteria) throughout the season. The associated functional potentials were related to heterotrophic-assimilatory and -dissimilatory pathways. Autotrophic Cyanobacterial lineages dominated the debris community at the beginning and end of summer, while heterotrophic Bacteroidota- and Proteobacteria-related phyla increased during the peak melt period. Predictive functional analyses based on taxonomy show a shift from predominantly phototrophy-related functions to heterotrophic assimilatory pathways as the melt-season progressed. This shift from autotrophic to heterotrophic communities within cryoconite holes can affect carbon drawdown and nutrient liberation from the glacier surface during the summer. In addition, the flushing out and export of cryoconite hole communities to the fjord could influence the biogeochemical dynamics of the fjord ecosystem.

Review

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms: Wonjae Kim, Yerim Park, Jaejoon Jung, Che Ok Jeon, Masanori Toyofuku, Jiyoung Lee, Woojun Park; J. Microbiol. 2024;62(3):249-260. Published online April 8, 2024; DOI: https://doi.org/10.1007/s12275-024-00115-2

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4 Citations

Abstract: The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O₂, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H₂O₂ are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Journal Articles

Impact of Elevational Gradients and Chemical Parameters on Changes in Soil Bacterial Diversity Under Semiarid Mountain Region: Salman Khan , Chun Han , Awais Iqbal , Chao Guan , Changming Zhao; J. Microbiol. 2023;61(10):903-915. Published online November 23, 2023; DOI: https://doi.org/10.1007/s12275-023-00085-x

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Abstract: Elevation gradients, often regarded as “natural experiments or laboratories”, can be used to study changes in the distribution of microbial diversity related to changes in environmental conditions that typically occur over small geographical scales. We obtained bacterial sequences using MiSeq sequencing and clustered them into operational taxonomic units (OTUs). The total number of reads obtained by the bacterial 16S rRNA sequencing analysis was 1,090,555, with an average of approximately 45,439 reads per sample collected from various elevations. The current study observed inconsistent bacterial diversity patterns in samples from the lowest to highest elevations. 983 OTUs were found common among all the elevations. The most unique OTUs were found in the soil sample from elevation_2, followed by elevation_1. Soil sample collected at elevation_6 had the least unique OTUs. Actinobacteria, Protobacteria, Chloroflexi were found most abundant bacterial phyla in current study. Ammonium nitrogen ( NH4 +-N), and total phosphate (TP) are the main factors influencing bacterial diversity at elevations_ 1. pH was the main factor influencing the bacterial diversity at elevations_2, elevation_3 and elevation_4. Our results provide new visions on forming and maintaining soil microbial diversity along an elevational gradient and have implications for microbial responses to environmental change in semiarid mountain ecosystems.

Crystal Structures of Plk1 Polo‑Box Domain Bound to the Human Papillomavirus Minor Capsid Protein L2‑Derived Peptide: Sujin Jung , Hye Seon Lee , Ho-Chul Shin , Joon Sig Choi , Seung Jun Kim , Bonsu Ku; J. Microbiol. 2023;61(8):755-764. Published online September 8, 2023; DOI: https://doi.org/10.1007/s12275-023-00071-3

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Abstract: Human papillomaviruses (HPVs) can increase the proliferation of infected cells during HPV-driven abnormalities, such as cervical cancer or benign warts. To date, more than 200 HPV genotypes have been identified, most of which are classified into three major genera: Alphapapillomavirus, Betapapillomavirus, and Gammapapillomavirus. HPV genomes commonly encode two structural (L1 and L2) and seven functional (E1, E2, E4–E7, and E8) proteins. L2, the minor structural protein of HPVs, not only serves as a viral capsid component but also interacts with various human proteins during viral infection. A recent report revealed that L2 of HPV16 recruits polo-like kinase 1 (Plk1), a master regulator of eukaryotic mitosis and cell cycle progression, for the delivery of viral DNA to mitotic chromatin during HPV16 infection. In this study, we verified the direct and potent interactions between the polo-box domain (PBD) of Plk1 and PBD-binding motif (S–S–pT–P)-containing phosphopeptides derived from L2 of HPV16/HPV18 (high-risk alphapapillomaviruses), HPV5b (low-risk betapapillomavirus), and HPV4 (low-risk gammapapillomavirus). Subsequent structural determination of the Plk1 PBD bound to the HPV18 or HPV4 L2-derived phosphopeptide demonstrated that they interact with each other in a canonical manner, in which electrostatic interactions and hydrogen bonds play key roles in sustaining the complex. Therefore, our structural and biochemical data imply that Plk1 is a broad binding target of L2 of various HPV genotypes belonging to the Alpha-, Beta-, and Gammapapillomavirus genera.

Tubulysins are Essential for the Preying of Ciliates by Myxobacteria: Uisang Yu , Jiha Kim , Seohui Park , Kyungyun Cho; J. Microbiol. 2023;61(6):627-632. Published online June 14, 2023; DOI: https://doi.org/10.1007/s12275-023-00056-2

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4 Citations

Abstract: Tubulysins are bioactive secondary metabolites produced by myxobacteria that promote microtubule disassembly. Microtubules are required for protozoa such as Tetrahymena to form cilia and flagella. To study the role of tubulysins in myxobacteria, we co-cultured myxobacteria and Tetrahymena. When 4000 Tetrahymena thermophila and 5.0 × 108 myxobacteria were added to 1 ml of CYSE medium and co-cultured for 48 h, the population of T. thermophila increased to more than 75,000. However, co-culturing tubulysin-producing myxobacteria, including Archangium gephyra KYC5002, with T. thermophila caused the population of T. thermophila to decrease from 4000 to less than 83 within 48 h. Almost no dead bodies of T. thermophila were observed in the culture medium. Co-culturing of T. thermophila and the A. gephyra KYC5002 strain with inactivation of the tubulysin biosynthesis gene led to the population of T. thermophila increasing to 46,667. These results show that in nature, most myxobacteria are preyed upon by T. thermophila, but some myxobacteria prey on and kill T. thermophila using tubulysins. Adding purified tubulysin A to T. thermophila changed the cell shape from ovoid to spherical and caused cell surface cilia to disappear.

Letter

Proposal of Flavihumibacter fluvii sp. nov. as a replacement name for the effectively published but invalidated epithet Flavihumibacter fluminis Park et al. 2022: Miri S. Park , Hyeonuk Sa , Ilnam Kang , Jang-Cheon Cho; J. Microbiol. 2023;61(6):649-651. Published online June 12, 2023; DOI: https://doi.org/10.1007/s12275-023-00057-1

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Abstract: The name Flavihumibacter fluminis Park et al. 2022, which was effectively published but invalidated, is an illegitimate homonymic epithet of Flavihumibacter fluminis Guo et al. 2023. The low 16S rRNA gene sequence similarity and genomic relatedness between the type strains IMCC34837T and RY-1T of the two homonymic species indicated that they are different species. To avoid further confusion, we propose a new name Flavihumibacter fluvii sp. nov. to replace the effectively published but invalidated homonymic epithet Flavihumibacter fluminis Park et al. 2022.

Journal Articles

Chemokine CCL6 Plays Key Role in the Inhibitory Effect of Vitamin A on Norovirus Infection: Heetae Lee , Giljae Lee , You-Hee Cho , Youngcheon Song , GwangPyo Ko; J. Microbiol. 2023;61(5):579-587. Published online May 26, 2023; DOI: https://doi.org/10.1007/s12275-023-00047-3

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Abstract: Norovirus (NoV) is the most common viral cause of acute gastroenteritis worldwide. Vitamin A has demonstrated the potential to protect against gastrointestinal infections. However, the effects of vitamin A on human norovirus (HuNoV) infections remain poorly understood. This study aimed to investigate how vitamin A administration affects NoV replication. We demonstrated that treatment with retinol or retinoic acid (RA) inhibited NoV replication in vitro based on their effects on HuNoV replicon-bearing cells and murine norovirus-1 (MNV-1) replication in murine cells. MNV replication in vitro showed significant transcriptomic changes, which were partially reversed by retinol treatment. RNAi knockdown of CCL6, a chemokine gene that was downregulated by MNV infection but upregulated by retinol administration, resulted in increased MNV replication in vitro. This suggested a role of CCL6 in the host response to MNV infections. Similar gene expression patterns were observed in the murine intestine after oral administration of RA and/or MNV-1.CW1. CCL6 directly decreased HuNoV replication in HG23 cells, and might indirectly regulate the immune response against NoV infection. Finally, relative replication levels of MNV-1.CW1 and MNV-1.CR6 were significantly increased in CCL6 knockout RAW 264.7 cells. This study is the first to comprehensively profile transcriptomes in response to NoV infection and vitamin A treatment in vitro, and thus may provide new insights into dietary prophylaxis and NoV infections.

Ship Hull‑Fouling Diatoms on Korean Research Vessels Revealed by Morphological and Molecular Methods, and Their Environmental Implications: Jaeyeong Park , Taehee Kim , Buhari Lawan Muhammad , Jang-Seu Ki; J. Microbiol. 2023;61(6):615-626. Published online May 25, 2023; DOI: https://doi.org/10.1007/s12275-023-00055-3

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Abstract: Ship biofouling is one of the main vectors for the introduction and global spread of non-indigenous organisms. Diatoms were the early colonizers of ship hulls; however, their community composition on ships is poorly understood. Herein, we investigated the diatom community on the hull samples collected from two Korean research vessels Isabu (IRV) and Onnuri (ORV) on September 2 and November 10, 2021, respectively. IRV showed low cell density (345 cells/cm2) compared to ORV (778 cells/cm2). We morphologically identified more than 15 species of diatoms from the two research vessels (RVs). The microalgae in both RVs were identified as Amphora, Cymbella, Caloneis, Halamphora, Navicula, Nitzschia, and Plagiogramma. Of them, the genus Halamphora was found to be predominant. However, both RVs had a varied dominant species with a significant difference in body size; Halamphora oceanica dominated at IRV, and Halamphora sp. at ORV, respectively. Molecular cloning showed similar results to morphological analysis, in which Halamphora species dominated in both RVs. The hull-attached species were distinct from species found in the water column. These results revealed diatoms communities that are associated with ship hull-fouling at an early stage of biofilm formation. Moreover, ships arriving from different regions could show some variation in species composition on their hull surfaces, with the potential for nonindigenous species introduction.

Description of Luteibacter aegosomatis sp. nov., Luteibacter aegosomaticola sp. nov., and Luteibacter aegosomatissinici sp. nov. isolated from the Intestines of Aegosoma sinicum Larvae: Hae-In Joe , Jee-Won Choi , June-Young Lee , Hojun Sung , Su-Won Jeong , Yun-Seok Jeong , Jae-Yun Lee , Jin-Woo Bae; J. Microbiol. 2023;61(6):603-613. Published online May 5, 2023; DOI: https://doi.org/10.1007/s12275-023-00051-7

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Abstract: Three novel bacterial strains, 321T, 335T, and 353T, were isolated from the intestines of Aegosoma sinicum larvae collected from Paju-Si, South Korea. The strains were Gram-negative, obligate aerobe and had rod-shaped cells with a single flagellum. The three strains belonged to the genus Luteibacter in the family Rhodanobacteraceae and shared < 99.2% similarity in their 16S rRNA gene sequence and < 83.56% similarity in thier whole genome sequence. Strains 321T, 335T, and 353T formed a monophyletic clade with Luteibacter yeojuensis KACC 11405T, L. anthropi KACC 17855T, and L. rhizovicinus KACC 12830T, with sequence similarities of 98.77–98.91%, 98.44–98.58%, and 97.88–98.02%, respectively. Further genomic analyses, including the construction of the Up-to-date Bacterial Core Gene (UBCG) tree and assessment of other genome-related indices, indicated that these strains were novel species belonging to the genus Luteibacter. All three strains contained ubiquinone Q8 as their major isoprenoid quinone and iso-C15:0 and summed feature 9 ( C16:0 10-methyl and/or iso-C17:1 ω9c) as their major cellular fatty acids. Phosphatidylethanolamine and diphosphatidylglycerol were the major polar lipids in all the strains. The genomic DNA G + C contents of strains 321T, 335T, and 353T were 66.0, 64.5, and 64.5 mol%, respectively. Based on multiphasic classification, strains 321T, 335T, and 353T were classified into the genus Luteibacter as the type strains of novel species, for which the names Luteibacter aegosomatis sp. nov., Luteibacter aegosomaticola sp. nov., and Luteibacter aegosomatissinici sp. nov. are proposed, respectively.

Review

Manganese Transporter Proteins in Salmonella enterica serovar Typhimurium: Nakyeong Ha , Eun-Jin Lee; J. Microbiol. 2023;61(3):289-296. Published online March 2, 2023; DOI: https://doi.org/10.1007/s12275-023-00027-7

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6 Citations

Abstract: The metal cofactors are essential for the function of many enzymes. The host restricts the metal acquisition of pathogens for their immunity and the pathogens have evolved many ways to obtain metal ions for their survival and growth. Salmonella enterica serovar Typhimurium also needs several metal cofactors for its survival, and manganese has been found to contribute to Salmonella pathogenesis. Manganese helps Salmonella withstand oxidative and nitrosative stresses. In addition, manganese affects glycolysis and the reductive TCA, which leads to the inhibition of energetic and biosynthetic metabolism. Therefore, manganese homeostasis is crucial for full virulence of Salmonella. Here, we summarize the current information about three importers and two exporters of manganese that have been identified in Salmonella. MntH, SitABCD, and ZupT have been shown to participate in manganese uptake. mntH and sitABCD are upregulated by low manganese concentration, oxidative stress, and host NRAMP1 level. mntH also contains a Mn2+- dependent riboswitch in its 5′ UTR. Regulation of zupT expression requires further investigation. MntP and YiiP have been identified as manganese efflux proteins. mntP is transcr!ptionally activated by MntR at high manganese levels and repressed its activity by MntS at low manganese levels. Regulation of yiiP requires further analysis, but it has been shown that yiiP expression is not dependent on MntS. Besides these five transporters, there might be additional transporters that need to be identified.

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