Journal of Microbiology

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Detection system− and strain−dependent diversity of de novo [PSI+] prion generation and phenotypes in Saccharomyces cerevisiae: Moonil Son; Received June 12, 2025 Accepted July 28, 2025 Published online September 18, 2025; DOI: https://doi.org/10.71150/jm.2506009 [Epub ahead of print]

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Abstract PDF: Yeast prion [PSI+], an amyloid form of the translation termination factor Sup35p/eRF3, causes translational stop codon readthrough by sequestering functional Sup35p. This unique phenotype may be analyzed via [PSI+]−suppressible nonsense alleles, and has greatly contributed to the advancement in yeast prion research. For comparing canonical reporters, like chromosomal ade1−14 or ade2−1, and plasmid-borne ura3−14, the de novo generation and characteristics of [PSI+] was investigated across common yeast laboratory strains (BY4741, 74D−694, and 779−6A). The results showed significant variability in [PSI+] induction frequency among strains. [PSI+] was successfully induced in BY4741 and frequently in 74D−694 (via Ade⁺ selection), but not in 779−6A. Notably, [PSI+] clones, even from identical genetic backgrounds, displayed vastly different nonsense suppression phenotypes depending on the reporter allele used; resulting in diverse growth patterns and suppression levels. Quantitative analyses revealed that prion seed counts fluctuated significantly based on the detection allele and observed phenotype. Furthermore, Sup35p aggregate visualization revealed distinct structural patterns between BY4741 and 74D−694, indicating strain-specific differences. Transferring [PIN+] prion variants from different strains into a common [psi−][pin−] background yielded similar [PSI+] inducibility and seed numbers, suggesting that the observed phenotypic and quantitative diversities of [PSI+] prions stem primarily from the interplay between the specific reporter detection system and the host strain's genetic background rather than solely from inherent differences in the initial [PIN+] prion or fundamental changes in the [PSI+] protein itself. This study underscores the crucial need to consider both the detection methodology and host genetic context for accurate prion variant characterization.

Reviews

Prions in Microbes: The Least in the Most: Moonil Son , Sia Han , Seyeon Lee; J. Microbiol. 2023;61(10):881-889. Published online September 5, 2023; DOI: https://doi.org/10.1007/s12275-023-00070-4

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Prions are infectious proteins that mostly replicate in self-propagating amyloid conformations (filamentous protein polymers) and consist of structurally altered normal soluble proteins. Prions can arise spontaneously in the cell without any clear reason and are generally considered fatal disease-causing agents that are only present in mammals. However, after the seminal discovery of two prions, [PSI+] and [URE3], in the eukaryotic model microorganism Saccharomyces cerevisiae, at least ten more prions have been discovered, and their biological and pathological effects on the host, molecular structure, and the relationship between prions and cellular components have been studied. In a filamentous fungus model, Podospora anserina, a vegetative incomparability-related [Het-s] prion that directly triggers cell death during anastomosis (hyphal fusion) was discovered. These prions in eukaryotic microbes have extended our understanding to overcome most fatal human prion/amyloid diseases. A prokaryotic microorganism (Clostridium botulinum) was reported to have a prion analog. The transcriptional regulators of C. botulinum-Rho can be converted into the self-replicating prion form ([RHO-X-C+]), which may affect global transcription. Here, we outline the major issues with prions in microbes and the lessons learned from the relatively uncovered microbial prion world.

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Yeast Prions: Discovery, Nature, Cellular Manipulation and Implication
Moonil Son
Journal of Microbiology and Biotechnology.2025;[Epub] CrossRef
A Story Between s and S: [Het-s] Prion of the Fungus Podospora anserina
Moonil Son
Mycobiology.2024; 52(2): 85. CrossRef

The osmotic stress response operon betIBA is under the functional regulation of BetI and the quorum-sensing regulator AnoR in Acinetobacter nosocomialis: Bindu Subhadra , Surya Surendran , Bo Ra Lim , Jong Sung Yim , Dong Ho Kim , Kyungho Woo , Hwa-Jung Kim , Man Hwan Oh , Chul Hee Choi; J. Microbiol. 2020;58(6):519-529. Published online May 27, 2020; DOI: https://doi.org/10.1007/s12275-020-0186-1

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Abstract PDF

Adaptation to changing environmental conditions is crucial for the survival of microorganisms. Bacteria have evolved various mechanisms to cope with osmotic stress. Here, we report the identification and functional characterization of the osmotic stress response operon, betIBA, in Acinetobacter nosocomialis. The betIBA operon encodes enzymes that are important for the conversion of choline to the osmoprotectant, glycine betaine. The betIBA operon is polycistronic and is under the regulation of the first gene, betI, of the same operon. A bioinformatics analysis revealed the presence of a BetI-binding motif upstream of the betIBA operon, and electrophoretic mobility shift assays confirmed the specific binding of BetI. An mRNA expression analysis revealed that expression of betI, betB, and betA genes is elevated in a betIeletion mutant compared with the wild type, confirming that the autorepressor BetI represses the betIBA operon in A. nosocomialis. We further found that the betIBA operon is under the transcriptional control of the quorum-sensing (QS) regulator, AnoR in, A. nosocomialis. A subsequent analysis of the impact of BetI on expression of the QS genes, anoR and anoI, demonstrated that BetI acts as a repressor of anoR and anoI. In addition, it was noticed that the osmotic stress response regulator, OmpR might play an important role in controlling the expression of betIBA operon in A. nosocomialis. Collectively, these data demonstrate that QS and osmotic stress-response systems are correlated in A. nosocomialis and that the expression of genes in both systems is finely tuned by various feedback loops depending on osmolarity conditions.

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Characterization of an Extracellular Lipase in Burkholderia sp. HY-10 Isolated from a Longicorn Beetle: Doo-Sang Park , Hyun-Woo Oh , Sun-Yeon Heo , Woo-Jin Jeong , Dong Ha Shin , Kyung Sook Bae , Ho-Young Park; J. Microbiol. 2007;45(5):409-417.; DOI: https://doi.org/2596 [pii]

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Abstract PDF: Burkholderia sp. HY-10 isolated from the digestive tracts of the longicorn beetle, Prionus insularis, produced an extracellular lipase with a molecular weight of 33.5 kDa estimated by SDS-PAGE. The lipase was purified from the culture supernatant to near electrophoretic homogenity by a one-step adsorption-desorption procedure using a polypropylene matrix followed by a concentration step. The purified lipase exhibited highest activities at pH 8.5 and 60°C. A broad range of lipase substrates, from C4 to C18 ρ-nitrophenyl esters, were hydrolyzed efficiently by the lipase. The most efficient substrate was ρ-nitrophenyl caproate (C6). A 2485 bp DNA fragment was isolated by PCR amplification and chromosomal walking which encoded two polypeptides of 364 and 346 amino acids, identified as a lipase and a lipase foldase, respectively. The N-terminal amino acid sequence of the purified lipase and nucleotide sequence analysis predicted that the precursor lipase was proteolytically modified through the secretion step and produced a catalytically active 33.5 kDa protein. The deduced amino acid sequence for the lipase shared extensive similarity with those of the lipase family I.2 of lipases from other bacteria. The deduced amino acid sequence contained two Cystein residues forming a disulfide bond in the molecule and three, well-conserved amino acid residues, Ser131, His330, and Asp308, which composed the catalytic triad of the enzyme.

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