Microbial Screening Based on the Mizoroki–Heck Reaction Permits Exploration of Hydroxyhexylitaconic-Acid-Producing Fungi in Soils

Abstract

Recently, we developed a unique microbial screening method based on the Mizoroki–Heck reaction for itaconic acid (IA)-producing fungi. This method revealed that 37 out of 240 fungal strains isolated from soils produce vinyl compounds, including IA. In this study, we further characterized these compounds in order to verify that the screening method permits the isolation of fungi that produce other vinyl compounds, excluding IA. HPLC analysis showed that 11 out of 37 isolated strains produced IA, similar to Aspergillus terreus S12-1. Surprisingly, the other 8 isolated strains produced two vinyl compounds with HPLC retention times different from that of IA. From these strains, the vinyl compounds of Aspergillus niger S17-5 were characterized. Mass spectrometric and NMR analyses showed that they were identical to 8-hydroxyhexylitaconic acid (8-HHIA) and 9-HHIA. This finding showed that 8-HHIA- and 9-HHIA-producing fungi, as well as IA-producing fungi, are ubiquitously found in soils. Neither 8-HHIA nor 9-HHIA showed antibacterial or anti-inflammatory activities. Interestingly, 8-HHIA and 9-HHIA showed cytotoxicity against the human cervical cancer cell line (HeLa) and human diploid cell line (MRC-5), and MRC-5 only, respectively, compared to IA at the same concentration. This study indicates that the screening method could easily discover fungi producing 8-HHIA and 9-HHIA in soils.

Caprylic acid enhances hydroxyhexylitaconic acid production in Aspergillus niger S17‐5

“…2020; Sano et al . 2020). Related studies have predicted that 9‐HHIA and 10‐HHIA are synthesized by the condensation of octanoyl‐CoA, which is derived from caprylic acid, with oxaloacetic acid (Gutiérrez et al .…”

“…Many IA derivatives with an IA skeletal structure have been found to be produced by fungi and lichens (Sano et al . 2020). Based on their structures, they can be roughly categorized into two groups, alkylitaconic acids and α‐methylene‐γ‐butyrolactones (Aso 2015).…”

“…As a result, we obtained a new fungus Aspergillus niger S17‐5 (Sano et al . 2020). Structural analyses showed that A. niger S17‐5 simultaneously produces two alkylitaconic acids, 9‐hydroxyhexylitaconic acid (9‐HHIA) and 10‐hydroxyhexylitaconic acid (10‐HHIA).…”

“…However, production titres of 9‐HHIA and 10‐HHIA in A. niger S17‐5 after 10 days of cultivation were 0·14 and 0·44 g l −1 respectively with flask cultivation (Sano et al . 2020). This suggests that the titres are low when they are used as bulk building blocks.…”

Correction: Sano, M., et al. Microbial Screening Based on the Mizoroki–Heck Reaction Permits Exploration of Hydroxyhexylitaconic-Acid-Producing Fungi in Soils. Microorganisms 2020, 8, 648

“…The authors wish to make the following correction to this paper [ 1 ]: the compound names ‘8-hydroxyhexylitaxconic acid’ and ‘9-hydroxyhexylitaconic acid’ should be ‘9-hydroxyhexylitaxconic acid’ and ‘10-hydroxyhexylitaconic acid’, respectively, throughout the manuscript. For this correction, the text in the graphical abstract and the carbon numbering in Figure 4 should be changed.…”