Journal of Microbiology

Research Article

LasB activation in Pseudomonas aeruginosa: Quorum sensing-mediated release of an auto-activation inhibitor: Cheol Seung Lee, Xi-Hui Li, Chae-Ran Jeon, Joon-Hee Lee; J. Microbiol. 2025;63(2):e2411005. Published online February 27, 2025; DOI: https://doi.org/10.71150/jm.2411005

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Abstract PDF: Pseudomonas aeruginosa secretes three major proteases: elastase B (LasB), protease IV (PIV), and elastase A (LasA), which play crucial roles in infection and pathogenesis. These proteases are activated sequentially from LasB in a proteolytic cascade, and LasB was previously thought to undergo auto-activation. However, our previous study suggested that LasB cannot auto-activate independently but requires additional quorum sensing (QS)-dependent factors for activation, as LasB remained inactive in QS-deficient P. aeruginosa (QS^-) even under artificial overexpression. In this study, we provide evidence for the existence of a LasB inhibitor in QS^- mutants: inactive LasB overexpressed in QS^- strains was in its processed form and could be reactivated upon purification; when full-length LasB was overexpressed in Escherichia coli, a heterologous bacterium lacking both LasB activators and inhibitors, the protein underwent normal processing and activation; and purified active LasB was significantly inhibited by culture supernatant (CS) from QS^- strains but not by CS from QS⁺ strains. These findings demonstrate that a LasB inhibitor exists in QS^- strains, and in its absence, LasB can undergo auto-activation without requiring an activator. Based on these results, we propose an updated hypothesis: the QS-dependent LasB activator functions by removing the LasB inhibitor rather than acting directly on LasB itself, thus preventing premature LasB activation until QS response is initiated.

Journal Articles

Analysis of phylogenetic markers for classification of a hydrogen peroxide producing Streptococcus oralis isolated from saliva by a newly devised differential medium: Ha Pham , Thi Dieu Thuy Tran , Youri Yang , Jae-Hyung Ahn , Hor-Gil Hur , Yong-Hak Kim; J. Microbiol. 2022;60(8):795-805. Published online July 14, 2022; DOI: https://doi.org/10.1007/s12275-022-2261-2

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Hydrogen peroxide (H2O2) is produced by alpha-hemolytic streptococci in aerobic conditions. However, the suitable method for detection of H2O2-producing streptococci in oral microbiota has not been setup. Here we show that o-dianisidine dye and horseradish peroxidase were useful in tryptic soy agar medium to detect and isolate H2O2-producing bacteria with the detection limit of one target colony in > 106 colony-forming units. As a proof, we isolated the strain HP01 (KCTC 21190) from a saliva sample using the medium and analyzed its characteristics. Further tests showed that the strain HP01 belongs to Streptococcus oralis in the Mitis group and characteristically forms short-chain streptococcal cells with a high capacity of acid tolerance and biofilm formation. The genome analysis revealed divergence of the strain HP01 from the type strains of S. oralis. They showed distinctive phylogenetic distances in their ROS-scavenging proteins, including superoxide dismutase SodA, thioredoxin TrxA, thioredoxin reductase TrxB, thioredoxin-like protein YtpP, and glutaredoxin- like protein NrdH, as well as a large number of antimicrobial resistance genes and horizontally transferred genes. The concatenated ROS-scavenging protein sequence can be used to identify and evaluate Streptococcus species and subspecies based on phylogenetic analysis.

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Alleviation of H2O2 toxicity by extracellular catalases in the phycosphere of Microcystis aeruginosa
Yerim Park, Wonjae Kim, Yeji Cha, Minkyung Kim, Woojun Park
Harmful Algae.2024; 137: 102680. CrossRef

Application of fast expectation-maximization microbial source tracking to discern fecal contamination in rivers exposed to low fecal inputs: Youfen Xu , Ganghua Han , Hongxun Zhang , Zhisheng Yu , Ruyin Liu; J. Microbiol. 2022;60(6):594-601. Published online April 18, 2022; DOI: https://doi.org/10.1007/s12275-022-1651-9

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