Biology subjects

Oiki, S.

Publications and source records attributed to Oiki, S..

5 recordsLinked to original sources

bioRxiv2026

HAC1 contributes to stress adaptation and virulence in the emerging fungal pathogen Candida auris

Candida auris (Candidozyma auris) is an emerging multidrug-resistant fungal pathogen that poses a significant global health threat. However, the molecular mechanisms underlying its virulence remain incompletely understood. In this study, we performed in vivo transcriptome analysis using an immunosuppressed mouse gastrointestinal infection model to identify genes associated with host-adaptation and virulence during infection. By comparing fungal transcriptomes obtained from colonization and dissemination sites with those from in vitro cultures, we identified genes that were consistently upregulated during infection. Among these genes, the unfolded protein response regulator HAC1 was selected as a candidate virulence-associated gene for further analysis. RT-PCR and sequencing analyses revealed that HAC1 mRNA in C. auris undergoes an unconventional splicing event of 287 bp that is enhanced under ER stress conditions. The excised region spans the annotated open reading frame boundary, suggesting that the translated region of HAC1 may require re-evaluation. Notably, a proportion of HAC1 transcripts appeared to be spliced even under non-stress conditions, indicating a detectable basal level of UPR activation. Differences in splicing dynamics were also observed among clade strains. Functional analyses demonstrated that deletion of HAC1 increased sensitivity to ER stress and heat stress. The HAC1 deletion mutant also exhibited reduced virulence in both Galleria mellonella and immunosuppressed mouse infection models, as evidenced by delayed host mortality and decreased fungal burdens, respectively. These findings indicate that HAC1 contributes to ER stress adaptation, thermotolerance, and survival in the host environment, and identify HAC1 as a virulence-associated gene in C. auris.

microbiology↗

bioRxiv2025

Molecular evolution and diversity of isomerase-reductase operons involved in bacterial metabolism of glycosaminoglycans

Glycosaminoglycans (GAGs), comprising uronic acids and amino sugars, are widely distributed in human tissues such as the intestine and oral cavity. Various bacteria colonize these tissues by assimilating GAGs. 4-Deoxy-L-threo-5-hexosulose uronate (DHU) is produced during the degradation of GAGs. Pectin, abundant in plants, is also degraded into DHU. DHU is metabolized in a stepwise manner by the isomerase KduI or DhuI, followed by the reductase KduD or DhuD. Previous studies have shown that the two genes encoding isomerase and reductase (kduI-kduD and dhuD-dhuI, respectively) are designated in an operon. Therefore, it was believed that dhuD-dhuI and kduI-kduD operons evolved independently. Nevertheless, the discovery of a hybrid kduI-dhuD operon raised questions regarding the evolution of these operons. This study was conducted to investigate the factors driving the diversity of operons through a pan-genomic phylogenetic analysis across 3550 bacterial strains. Seven types of DHU metabolism-related operons were identified. The phylum Bacteroidota possesses a hybrid-type kduI-dhuD operon rather than kduI-kduD or kduD-kduI operon. The phylum Bacillota, but not Pseudomonadota or Bacteroidota, possesses the dhuD-dhuI operon; however, dhuI-dhuD operon was not detected in any bacterial strain. Although DHU is generated from the degradation of oligomerized GAG by an unsaturated glucuronyl hydrolase (UGL), the UGL gene was found in strains positive for kduD-kduI, dhuD-dhuI, kduI-dhuD, and dhuD-kduI operons at high ratios, indicating that the acquisition of these operons is advantageous for colonization on human hosts. (230 words) IMPORTANCEGlycosaminoglycans (GAGs), crucial components of the extracellular matrix, play a vital role in host infection by pathogenic bacteria as well as in the colonization of the host by commensal bacteria. The isomerases KduI and DhuI are nonhomologous isofunctional enzymes. The dhuD-dhuI operon is well conserved within certain phyla and appears to have a strong association with GAG metabolism. In contrast, the kduI system is more widely distributed across various species. Based on the possession ratios of genes encoding each enzyme that produces 4-deoxy-L-threo-5-hexosulose uronate, this study indicated that the substrates targeted by each metabolic system vary depending on the specific operon type.

microbiology↗

bioRxiv2022

Binding of cardiolipin to the KcsA channel at the membrane outer leaflet allosterically opens the inner gate

Membrane proteins embedded in the membrane undergo changes in their actions under the influence of membrane lipids. Here, we present a novel type of lipid action on the potassium channel KcsA from Streptomyces lividans. Cardiolipin is present in various cellular membranes, including the host membrane of KcsA. Although the M0 domain, a nontransmembrane helix, is known to sense anionic lipids in the inner leaflet, we found that divalent anionic cardiolipin in the outer leaflet of the membrane interacts with positively charged residues, Arg64 and Arg89, on the extracellular side of the transmembrane domain. This binding propagates its action across the membrane toward the intracellular region of KcsA, thus, opening the inner gate. Such a long-range allosteric effect has not been found for channel-lipid interactions.

biophysics↗

bioRxiv2021

Intimate genetic relationships and fungicide resistance in multiple strains of human pathogenic fungus Aspergillus fumigatus isolated from a plant bulb

Fungal infections are increasingly dangerous because of environmentally-dispersed resistance to antifungal drugs. Azoles are commonly used antifungal drugs, but they are also used as fungicides in agriculture, which may enable enrichment of azole-resistant strains of the human pathogen Aspergillus fumigatus in the environment. Understanding of environmental dissemination and enrichment of genetic variation associated with azole resistance in A. fumigatus is required to suppress resistant strains. Here, we focused on eight strains of azole-resistant A. fumigatus isolated from a single tulip bulb for sale in Japan. This set includes strains with TR34/L98H/T289A/I364V/G448S and TR46/Y121F/T289A/S363P/I364V/G448S mutations in the cyp51A gene, which showed higher tolerance to several azoles than strains harboring TR46/Y121F/T289A mutation. The strains were typed by microsatellite typing, single nucleotide polymorphism profiles, and mitochondrial and nuclear genome analyses. The strains grouped differently using each typing method, suggesting historical genetic recombination among the strains. Our data also revealed that some strains isolated from the tulip bulb showed tolerance to other classes of fungicide, such as QoI and carbendazim, followed by related amino acid alterations in the target proteins. Considering spatial-temporal factors, plant bulbs are an excellent environmental niche for fungal strains to encounter partners, and to obtain and spread resistance-associated mutations.

microbiology↗

bioRxiv2018

Streptococcal phosphotransferase system imports unsaturated hyaluronan disaccharide derived from host extracellular matrices

Certain bacterial species target the polysaccharide glycosaminoglycans (GAGs) of animal extracellular matrices for colonization and/or infection. GAGs such as hyaluronan and chondroitin sulfate consist of repeating disaccharide units of uronate and amino sugar residues, and are depolymerized to unsaturated disaccharides by bacterial extracellular or cell-surface polysaccharide lyase. The disaccharides are degraded and metabolized by cytoplasmic enzymes such as unsaturated glucuronyl hydrolase, isomerase, and reductase. The genes encoding these enzymes are assembled to form a GAG genetic cluster. Here, we demonstrate the Streptococcus agalactiae phosphotransferase system (PTS) for import of unsaturated hyaluronan disaccharide. S. agalactiae NEM316 was found to depolymerize and assimilate hyaluronan, whereas its mutant with a disruption in PTS genes included in the GAG cluster was unable to grow on hyaluronan, while retaining the ability to depolymerize hyaluronan. Using toluene-treated wild-type cells, the PTS import activity of unsaturated hyaluronan disaccharide was significantly higher than that observed in the absence of the substrate. In contrast, the PTS mutant was unable to import unsaturated hyaluronan disaccharide, indicating that the corresponding PTS is the only importer of fragmented hyaluronan, which is suitable for PTS to phosphorylate the substrate at the C-6 position. The three-dimensional structure of streptococcal EIIA, one of the PTS components, was found to contain a Rossman-fold motif by X-ray crystallization. Docking of EIIA with another component EIIB by modeling provided structural insights into the phosphate transfer mechanism. This study is the first to identify the substrate (unsaturated hyaluronan disaccharide) recognized and imported by the streptococcal PTS.\n\nIMPORTANCE (118/120 words)The PTS identified in this work imports sulfate group-free unsaturated hyaluronan disaccharide as a result of the phosphorylation of the substrate at the C-6 position. S. agalactiae can be indigenous to animal hyaluronan-rich tissues owing to the bacterial molecular system for fragmentation, import, degradation, and metabolism of hyaluronan. Distinct from hyaluronan, most GAGs, which are sulfated at the C-6 position, are unsuitable for PTS due to its inability to phosphorylate the substrate. More recently, we have identified a solute-binding protein-dependent ABC transporter in a pathogenic Streptobacillus moniliformis as an importer of sulfated and non-sulfated fragmented GAGs without any substrate modification. Our findings regarding PTS and ABC transporter shed light on bacterial clever colonization/infection system targeting various animal GAGs.

microbiology↗