Journal of Microbiology

Article

Functional characterization of spike RBD mutations in SARS-CoV-2 Omicron-derived subvariants KP.3.1.1, LP.8.1, and NB.1.8.1.: Yeong Jun Kim, Seon Jae Jeong, Hye-Ra Lee; Received November 17, 2025 Accepted January 14, 2026 Published online April 6, 2026; DOI: https://doi.org/10.71150/jm.2511014 [Epub ahead of print]

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Abstract PDF: Following the global spread of SARS-CoV-2 Omicron (B.1.1.529), its subvariants KP.3.1.1, LP.8.1, and NB.1.8.1 disseminated worldwide. By April 2025, the epidemiological landscape of these subvariants had become distinct, with LP.8.1 emerging as the predominant variant, KP.3.1.1 persisting as a co-circulating variant under monitoring (VUM), and NB.1.8.1 exhibiting a significant increase in prevalence. Despite their epidemiological prominence, the functional consequences of spike mutations defining these emerging subvariants remain poorly understood. Here, we systematically dissected the entry properties conferred by their receptor-binding domain (RBD) mutations using a pseudovirus system. Our results demonstrate that all three subvariants exhibited substantially higher infectivity than ancestral Omicron. Unexpectedly, this enhanced infectivity occurred despite reduced ACE2 binding affinity. Rather, increased viral entry consistently correlated with elevated spike cleavage efficiency and fusogenicity, suggesting a compensatory evolutionary strategy in which enhanced spike processing and fusion contribute to enhanced entry despite reduced receptor engagement. These findings provide a virological explanation for the accelerated global spread of these subvariants and highlight the importance of monitoring functional shifts in spike-mediated entry that may influence SARS-CoV-2 transmission dynamics.

Review

Envelope‑Stress Sensing Mechanism of Rcs and Cpx Signaling Pathways in Gram‑Negative Bacteria: Seung-Hyun Cho , Kilian Dekoninck , Jean-Francois Collet; J. Microbiol. 2023;61(3):317-329. Published online March 9, 2023; DOI: https://doi.org/10.1007/s12275-023-00030-y

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The global public health burden of bacterial antimicrobial resistance (AMR) is intensified by Gram-negative bacteria, which have an additional membrane, the outer membrane (OM), outside of the peptidoglycan (PG) cell wall. Bacterial twocomponent systems (TCSs) aid in maintaining envelope integrity through a phosphorylation cascade by controlling gene expression through sensor kinases and response regulators. In Escherichia coli, the major TCSs defending cells from envelope stress and adaptation are Rcs and Cpx, which are aided by OM lipoproteins RcsF and NlpE as sensors, respectively. In this review, we focus on these two OM sensors. β-Barrel assembly machinery (BAM) inserts transmembrane OM proteins (OMPs) into the OM. BAM co-assembles RcsF, the Rcs sensor, with OMPs, forming the RcsF-OMP complex. Researchers have presented two models for stress sensing in the Rcs pathway. The first model suggests that LPS perturbation stress disassembles the RcsF-OMP complex, freeing RcsF to activate Rcs. The second model proposes that BAM cannot assemble RcsF into OMPs when the OM or PG is under specific stresses, and thus, the unassembled RcsF activates Rcs. These two models may not be mutually exclusive. Here, we evaluate these two models critically in order to elucidate the stress sensing mechanism. NlpE, the Cpx sensor, has an N-terminal (NTD) and a C-terminal domain (CTD). A defect in lipoprotein trafficking
results
in NlpE retention in the inner membrane, provoking the Cpx response. Signaling requires the NlpE NTD, but not the NlpE CTD; however, OM-anchored NlpE senses adherence to a hydrophobic surface, with the NlpE CTD playing a key role in this function.

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Article

Development of a neutralization assay based on the pseudotyped chikungunya virus of a Korean isolate: Woo-Chang Chung , Kwang Yeon Hwang , Suk-Jo Kang , Jae-Ouk Kim , Moon Jung Song; J. Microbiol. 2020;58(1):46-53. Published online November 25, 2019; DOI: https://doi.org/10.1007/s12275-020-9384-0

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Abstract PDF

The Chikungunya virus (CHIKV) belongs to the Alphavirus genus of Togaviridae family and contains a positive-sense single stranded RNA genome. Infection by this virus mainly causes sudden high fever, rashes, headache, and severe joint pain that can last for several months or years. CHIKV, a mosquito- borne arbovirus, is considered a re-emerging pathogen that has become one of the most pressing global health concerns due to a rapid increase in epidemics. Because handling of CHIKV is restricted to Biosafety Level 3 (BSL-3) facilities, the evaluation of prophylactic vaccines or antivirals has been substantially hampered. In this study, we first identified the whole structural polyprotein sequence of a CHIKV strain isolated in South Korea (KNIH/2009/77). Phylogenetic analysis showed that this sequence clustered within the East/ Central/South African CHIKV genotype. Using this sequence information, we constructed a CHIKV-pseudotyped lentivirus expressing the structural polyprotein of the Korean CHIKV isolate (CHIKVpseudo) and dual reporter genes of green fluorescence protein and luciferase. We then developed a pseudovirus-based neutralization assay (PBNA) using CHIKVpseudo. Results from this assay compared to those from the conventional plaque reduction neutralization test showed that our PBNA was a reliable and rapid method to evaluate the efficacy of neutralizing antibodies. More importantly, the neutralizing activities of human sera from CHIKVinfected individuals were quantitated by PBNA using CHIKVpseudo. Taken together, these results suggest that our PBNA for CHIKV may serve as a useful and safe method for testing the neutralizing activity of antibodies against CHIKV in BSL-2 facilities.

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Validation Study

Comparison of JEV Neutralization Assay Using Pseudotyped JEV with the Conventional Plaque-Reduction Neutralization Test: Hee-Jung Lee , Kyung-Il Min , Ki Hoon Park , Hyo Jung Choi , Min-Kyoung Kim , Chi-Young Ahn , Young-Jin Hong , Young Bong Kim; J. Microbiol. 2014;52(5):435-440. Published online March 7, 2014; DOI: https://doi.org/10.1007/s12275-014-3529-y

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Abstract PDF

We previously reported the development of a neutralization assay system for evaluating Japanese Encephalitis Virus (JEV) neutralizing antibody (NAb) using pseudotyped-JEV (JEV- PV). JEV-PV-based neutralization assay offers several advan-tages compared with the current standard plaque-reduc-tion neutralization test (PRNT), including simplicity, safety, and speed. To evaluate the suitability of the JEV-PV assay as new replacement neutralization assay, we compared its repeatability, reproducibility, specificity, and correlated its results with those obtained using the PRNT. These analyses showed a close correlation between the results obtained with the JEV-PV assay and the PRNT, using the 50% plaque re-duction method as a standard for measuring NAb titers to JEV. The validation results met all analytical acceptance criteria. These results suggest that the JEV-PV assay could serve as a safe and simple method for measuring NAb titer against JEV and could be used as an alternative approach for assaying the potency of JEV neutralization.

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Development of a neutralization assay based on the pseudotyped chikungunya virus of a Korean isolate
Woo-Chang Chung, Kwang Yeon Hwang, Suk-Jo Kang, Jae-Ouk Kim, Moon Jung Song
Journal of Microbiology.2020; 58(1): 46. CrossRef
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