石井 雅樹

ABSTRACT The resistance of Trichophyton indotineae to azoles is mainly due to the overexpression of TinCYP51B, resulting from additional copies of this gene in two types of strains (type I and type II). Due to its large size and the significant number of duplicated blocks, whole-genome sequencing has been unable to cover the entire TinCYP51B locus. Through optical genome mapping (OGM), we have successfully determined the copy number of the TinCYP51B gene in the genomes of resistant strains. The TinCYP51B copy number was lower in the type I strains than in the type II strains, while the TinCYP51B expression level was higher in the type I strains. To explain this paradox, we have revealed that polycistronic transcription of multiple TinCYP51B open reading frames (ORFs) alongside monocistronic transcription occurs in type I azole-resistant strains. In contrast, type II strains generated only the transcripts encoding one CYP51B polypeptide. OGM has also revealed that a 970 kb region on chromosome 3 is inverted in type I strains and the azole-susceptible strain TIMM20115, as compared to type II strains and the azole-susceptible strain TIMM20114. This has led to the hypothesis that under azole stress, type I resistant strains originate from susceptible strains such as TIMM20115, which possesses a single TinCYP51B gene. Conversely, it is believed that type II azole-resistant strains evolve from susceptible strains such as TIMM20114, which also has only one TinCYP51B gene. In conclusion, strains of Trichophyton indotineae can be divided into two groups in which a distinct type of resistance has developed.

Abstract Dominance of Bacillus species on conventional agar media often hampers the isolation of taxonomically diverse soil bacteria (i.e., “ Bacillus dominance”). To overcome this Bacillus dominance, we developed a novel agar medium containing leaf mold extract (LME) and assessed its utility for isolating microorganisms from soil samples. For comparison, conventional yeast malt extract agar (YME agar) was used as a control. 16S rRNA gene sequencing revealed that colonies cultured on YME agar predominantly consisted of Bacillus -related bacteria, whereas LME agar enabled the growth of a wider variety of taxa, particularly actinomycetes such as Streptomyces . Notably, LME agar supported a higher diversity of soil bacterial isolates even from samples with a low abundance of Bacillus -related species. Among the 138 isolates recovered from LME agar, some either exhibited very low 16S rRNA gene sequence identity to known species in public databases, or failed to yield 16S rRNA amplicons with conventional universal primers, suggesting the presence of previously uncharacterized or novel taxa. Furthermore, one unidentified isolate failed to grow on standard nutrient media (YME, BHI, LB10, or TSB), but proliferated in liquid leaf mold extract, indicating a specific nutrient dependency. These findings demonstrate that LME agar can facilitate the isolation of a broader spectrum of soil microorganisms (including rare and previously uncultured species) not readily recoverable on common basal media. Incorporation of ecosystem-derived substrates into culture media may greatly enhance the discovery and study of novel microbial diversity from environmental samples. Importance Soil contains a vast number of microorganisms, many of which remain undiscovered due to limitations in standard laboratory methods. A major issue is the overgrowth of Bacillus species on conventional media, which suppresses the growth of other bacteria. To address this, we developed a new agar medium using leaf mold extract (LME) and found it successfully supported the growth of a much wider variety of soil bacteria, including rare species. Some of the isolated microbes could not be identified using standard genetic tools, and one unique strain only grew in LME-based media, indicating a special nutrient requirement. These findings show that using natural environmental components like leaf mold can help scientists grow and study bacteria that were previously missed. This approach can expand our understanding of microbial diversity and may lead to the discovery of new microbes with potential applications in agriculture, medicine, or environmental science.

ABSTRACT Lysin motif (LysM) domain-containing receptors are evolutionarily conserved pattern recognition receptors (PRRs) that serve as key mediators of glycan sensing and innate immune activation in plants and mammals. In invertebrates, however, their role in activating innate immunity remains poorly understood, although some evidence for immunosuppressive functions exists. In this study, we performed in silico structural analyses and identified a putative Bombyx mori LYSMD3 homolog ( XP_004933441.1 ). This protein exhibits high structural similarity in the LysM domain to human LYSMD3, with a root-mean-square deviation (RMSD) of 0.559 Å, indicating close structural alignment. RNA-seq analysis of hemocytes isolated from silkworm larvae injected with N -acetylchitohexaose (GN6), a chitin-derived oligosaccharide and known ligand of human LYSMD3, revealed transcriptional activation of innate immune effectors, including antimicrobial peptide (AMP) genes such as cecropins . GN6 also induced cecropin transcription in isolated hemocytes in vitro , and Western blotting of hemolymph confirmed elevated cecropin B protein levels. Furthermore, GN6 and chitin significantly improved survival outcomes against P. aeruginosa infection, with median effective doses (ED₅₀) values of 0.62 and 0.48  µg/larva, respectively. In contrast, N -acetylglucosamine (GlcNAc) and shorter oligosaccharides (GN2–GN5) were ineffective. These findings provide the first molecular-level evidence of a putative glycan receptor in silkworms based on the structural similarity to known LysM domains. Moreover, GN6-induced antimicrobial peptide expression and enhanced infection resistance demonstrate immune activation in this model, supporting an evolutionarily conserved glycan-sensing pathway in invertebrates.

ABSTRACT Pathogenic fungi pose significant societal challenges due to limited therapeutic targets resulting from the eukaryotic nature of fungi. This limitation emphasizes the importance of enhancing susceptibility to inhibitors of Cyp51, a crucial enzyme in ergosterol biosynthesis targeted by azole antifungals. In Cyp51 isozyme deletion strains (Δ cyp51A and Δ cyp51B ) of Trichophyton rubrum , the predominant dermatophyte species, we found that Cyp51B is essential for basal mycelial growth, while Cyp51A functions as an inducible isozyme associated with azole tolerance. Based on these differential functions, we hypothesized that each isozyme would show distinct susceptibility to azole antifungals. Our study demonstrated that most azoles exhibited increased antifungal activity against Δ cyp51A , while select agents demonstrated increased antifungal activity against Δ cyp51B . Remarkably, fluconazole, sulconazole, and imazalil exhibited relatively increased activity against Δ cyp51A , whereas prochloraz demonstrated increased activity against Δ cyp51B . Combining these isozyme-selective agents exerted synergistic effects against the wild-type strain and the parent ku80 -knockout strain but not against individual Cyp51 knockout mutants. Our data revealed that the two Cyp51 isozymes can be selectively inhibited by different azole antifungals, resulting in a synergistic effect when combined. This synergistic effect was also observed on another fungal species, Aspergillus welwitschiae , which also has two Cyp51 isozymes. These data demonstrate that combining azole antifungals with different Cyp51 isozyme selectivities exerts synergistic effects against fungi possessing multiple Cyp51 isozymes. These findings advance antifungal therapeutic strategies by demonstrating that the combination of antifungals with different Cyp51 isozyme selectivities offers a promising approach for treating fungal infections, opening new avenues for isozyme-specific drug development.