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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A Story Between s and S: [Het-s] Prion of the Fungus
Podospora anserina
Moonil Son Mycobiology.2024; 52(2): 85. CrossRef
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.
Citations
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Metabolome analysis revealed the critical role of betaine for arsenobetaine biosynthesis in the marine medaka (Oryzias melastigma) Qianyu Zhao, Qiao-Guo Tan, Wen-Xiong Wang, Peng Zhang, Zijun Ye, Liping Huang, Wei Zhang Environmental Pollution.2024; 359: 124612. CrossRef
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luxI/R
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