Aspergillus fumigatus is the major causative fungus of aspergillosis, and many studies have explored the relationship between A. fumigatus and pathogenicity. In the current study, we focused on a fucose-specific lectin, FleA, as a novel molecule which related to the pathogenicity of A. fumigatus. The disruption of the fleA gene did not lead to clear morphological changes compared to parental strain under several stress conditions in culture, but germination become earlier. In comparison with parental strain, the pathogenicity of disruptant was enhanced in a mouse infection model. The pattern of conidial phagocytosis and adhesion to cultured cells did not explain this enhanced pathogenicity. FleA was reported to contain six conserved fucose-binding sites; the analysis of constructed FleA point mutants revealed nonequivalent contribution of the fucose-binding sites to fucose binding. Based on the immune response induced in the cultured cells upon exposure to wild-type and mutant FleA, we propose a model of the FleA molecule in A. fumigatus infection.

Aspergillus flavus produces aflatoxin, a carcinogenic fungal toxin that poses a threat to the agricultural and food industries. There is a concern that the distribution of aflatoxin-producing A. flavus is expanding in Japan due to climate change, and it is necessary to understand what types of strains inhabit. In this study, we sequenced the genomes of four Aspergillus strains isolated from agricultural fields in the Ibaraki prefecture of Japan and identified their genetic variants. Phylogenetic analysis based on single-nucleotide variants revealed that the two aflatoxin-producing strains were closely related to A. flavus NRRL3357, whereas the two non-producing strains were closely related to the RIB40 strain of Aspergillus oryzae, a fungus widely used in the Japanese fermentation industry. A detailed analysis of the variants in the aflatoxin biosynthetic gene cluster showed that the two aflatoxin-producing strains belonged to different morphotype lineages. RT-qPCR results indicated that the expression of aflatoxin biosynthetic genes was consistent with aflatoxin production in the two aflatoxin-producing strains, whereas the two non-producing strains expressed most of the aflatoxin biosynthetic genes, unlike common knowledge in A. oryzae, suggesting that the lack of aflatoxin production was attributed to genes outside of the aflatoxin biosynthetic gene cluster in these strains.

Nocardithiocin is a thiopeptide compound produced by the pathogenic actinomycete Nocardia pseudobrasiliensis that displays activity against Gram-positive bacteria including drug-resistant Mycobacterium tuberculosis. However, the clinical use of nocardithiocin is hampered by light sensitivity and low water solubility. To improve these properties, the sixth amino acid of core peptide was substituted for other 19 amino acids by modifying the gene sequence of precursor peptide. Ten amino acids were successfully substituted to produce 1–3 novel compounds, of which six were the expected nocardithiocin derivatives. The compounds were tested for their stability, solubility, and antimicrobial activity. Of the 17 compounds produced, ten displayed antibiotic activity and two of them improved MIC value to bacteria. Furthermore, nocardithiocin and all derivatives were stable to the light. The substitution of amino acid sequence in precursor peptide could lead the successful production of nocardithiocin derivatives and alter its property. This report represents the first step of nocardithiocin utilization, and amino acid substitution technique can be used to create desirable nocardithiocin derivatives.