Fungal Secondary Metabolites and Their Fundamental Roles in Human Mycoses

A Genome-Wide Comparison of Rice False Smut Fungus Villosiclava virens Albino Strain LN02 Reveals the Genetic Diversity of Secondary Metabolites and the Cause of Albinism

Rice false smut (RFS) caused by Villosiclava virens (anamorph: Ustilaginoidea virens) has become one of the most destructive fungal diseases to decrease the yield and quality of rice grains. An albino strain LN02 was isolated from the white RFS balls collected in the Liaoning Province of China in 2019. The strain LN02 was considered as a natural albino mutant of V. virens by analyzing its phenotypes, internal transcribed spacer (ITS) conserved sequence, and biosynthesis gene clusters (BGCs) for secondary metabolites. The total assembled genome of strain LN02 was 38.81 Mb, which was comprised of seven nuclear chromosomes and one mitochondrial genome with an N50 value of 6,326,845 bp and 9339 protein-encoding genes. In addition, the genome of strain LN02 encoded 19 gene clusters for biosynthesis of secondary metabolites mainly including polyketides, terpenoids and non-ribosomal peptides (NRPs). Four sorbicillinoid metabolites were isolated from the cultures of strain LN02. It was found that the polyketide synthase (PKS)-encoding gene uspks1 for ustilaginoidin biosynthesis in strain LN02 was inactivated due to the deletion of four bases in the promoter sequence of uvpks1. The normal uvpks1 complementary mutant of strain LN02 could restore the ability to synthesize ustilaginoidins. It demonstrated that deficiency of ustilaginoidin biosynthesis is the cause of albinism for RFS albino strain LN02, and V. virens should be a non-melanin-producing fungus. This study further confirmed strain LN02 as a white phenotype mutant of V. virens. The albino strain LN02 will have a great potential in the development and application of secondary metabolites. The physiological and ecological functions of ustilaginoidins in RFS fungus are needed for further investigation.

Microfluidic System for Rapid Detection of Airborne Pathogenic Fungal Spores

Airborne fungi, including Aspergillus species, are the major causes of human asthma. Direct capture and analysis of pathogenic fungi in indoor air is important for disease prevention and control. In this paper, we demonstrated an integrated microfluidic system capable of enrichment and high-throughput detection for airborne fungal spores of Aspergillus niger, a well-known allergenic harmful species. The microfluidic system allowed semiquantitative detection of Aspergillus niger spores based on immunofluorescence analysis. To assess its contaminated level, the whole analysis time could be completed in 2-3 h including ∼1 h of enrichment and ∼1 h of target detection. The detection limit was ∼20 spores, equivalent to ∼300 spores·m^-3 of the concerned targets in air. In addition, the microfluidic system has integrated sampling and sample analysis to avoid additional sample concentration step, showing the potential for point-of-care detection for other pathogenic fungal spores.

Biodegradable siderophores: survey on their production, chelating and complexing properties

The academic and industrial research on the interactions of complexing agents with the environment has received more attention for more than half a century ago and has always been concerned with the applications of chelating agents in the environment. In contrast, in recent years, an increasing scholarly interest has been demonstrated in the chemical and biological degradation of chelating agents. This is reflected by the increasing number of chelating agents-related publications between 1950 and middle of 2016. Consequently, the discovery of new green biodegradable chelating agents is of great importance and has an impact in the non-biodegradable chelating agent’s replacement with their green chemistry analogs. To acquire iron, many bacteria growing aerobically, including marine species, produce siderophores, which are low-molecular-weight compounds produced to facilitate acquisition of iron. To date and to the best of our knowledge, this is a concise and complete review article of the current and previous relevant studies conducted in the field of production, purification of siderophore compounds and their metal complexes, and their roles in biology and medicine.

A novel automethylation reaction in the Aspergillus nidulans LaeA protein generates S-methylmethionine

The filamentous fungi in the genus Aspergillus are opportunistic plant and animal pathogens that can adapt to their environment by producing various secondary metabolites, including lovastatin, penicillin, and aflatoxin. The synthesis of these small molecules is dependent on gene clusters that are globally regulated by the LaeA protein. Null mutants of LaeA in all pathogenic fungi examined to date show decreased virulence coupled with reduced secondary metabolism. Although the amino acid sequence of LaeA contains the motifs characteristic of seven-β-strand methyltransferases, a methyl-accepting substrate of LaeA has not been identified. In this work we did not find a methyl-accepting substrate in Aspergillus nidulans with various assays, including in vivo S-adenosyl-[methyl-(3)H]methionine labeling, targeted in vitro methylation experiments using putative protein substrates, or in vitro methylation assays using whole cell extracts grown under different conditions. However, in each experiment LaeA was shown to self-methylate. Amino acid hydrolysis of radioactively labeled LaeA followed by cation exchange and reverse phase chromatography identified methionine as the modified residue. Point mutations show that the major site of modification of LaeA is on methionine 207. However, in vivo complementation showed that methionine 207 is not required for the biological function of LaeA. LaeA is the first protein to exhibit automethylation at a methionine residue. These findings not only indicate LaeA may perform novel chemistry with S-adenosylmethionine but also provide new insights into the physiological function of LaeA.