Photoclick reaction for rapid and simple fluorescence detection of itaconic acid and its derivatives in fungal cultures

Itaconic acid (IA) and its derivatives produced by fungi have significant potential as industrial feedstocks. We recently developed a method for the detection of these compounds based on their terminal C-C double bonds. However, the presence of reducing agents, such as glucose and other fungal metabolites, leads to undesirable side reactions, and consequently, deteriorates the detection specificity. Therefore, we developed a fluorescence detection method for IA and its derivatives underpinned by a photoclick reaction. The photoclick reaction between conjugated IA and 5-(4-methoxyphenyl)-2-phenyl-2H-tetrazole under UV irradiation affords a fluorescent product. No fluorescence was detected when succinic acid was subjected to the reaction, indicating that a terminal C-C double bond is required to induce fluorescence. Optimal reaction conditions were determined to be a combination of 80% final dimethyl sulfoxide concentration, 30-s UV irradiation, and a pH of 2. Two weeks after the reaction at 4 °C, 89.0% of the initial intensity was retained, indicating that the reaction product was relatively stable. Glucose and kojic acid did not induce fluorescence after the reaction, indicating that these reducing agents did not affect fluorescence. IA was detected in a culture of Aspergillus terreus, and its quantification using the photoclick reaction was in agreement with the results obtained using high-performance liquid chromatography analysis. Interestingly, the IA derivative avenaciolide present in submillimolar quantities was also detectable in a culture of Aspergillus avenaceus using this method. The established method will enable the development of high-throughput screening methods to identify fungi that produce IA and its derivatives.

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

AIM

Aspergillus niger S17-5 produces two alkylitaconic acids, 9-hydroxyhexylitaconic acid (9-HHIA) and 10-hydroxyhexylitaconic acid (10-HHIA), which have cytotoxic and polymer building block properties. In this study, we characterized the production of 9-HHIA and 10-HHIA by addition of their expected precursor, caprylic acid, to a culture of A. niger S17-5, and demonstrated batch fermentation of 9-HHIA and 10-HHIA in a jar fermenter with DO-stat.

METHODS AND RESULTS

Production titres of 9-HHIA and 10-HHIA from 3% glucose in a flask after 25 days cultivation were 0·35 and 1·01 g l^-1 respectively. Addition of 0·22 g l^-1 of caprylic acid to a suspension of resting cells of A. niger S17-5 led to 32% enhancement of total 9-HHIA and 10-HHIA production compared to no addition. No enhancement of the production of 9-HHIA or 10-HHIA by the addition of oxaloacetic acid was observed. Addition of caprylic acid to the culture at mid-growth phase was more suitable for 9-HHIA and 10-HHIA production due to less cell growth inhibition by caprylic acid. DO-stat batch fermentation with 3% glucose and 14·4 g l^-1 of caprylic acid in a 1·5 l jar fermenter resulted in the production titres of 9-HHIA and 10-HHIA being 0·48 and 1·54 g l^-1 respectively after 10 days of cultivation.

CONCLUSIONS

Addition of caprylic acid to the culture of A. niger S17-5 enhances 9-HHIA and 10-HHIA production.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results suggest that 9-HHIA and 10-HHIA are synthesized with octanoyl-CoA derived from caprylic acid, and that the supply of octanoyl-CoA is a rate-limiting step in 9-HHIA and 10-HHIA production. To the best of our knowledge, this is the first report regarding the fermentation of naturally occurring itaconic acid derivatives in a jar fermenter.

Itaconic acid derivatives: structure, function, biosynthesis, and perspectives

Itaconic acid possessing a vinylidene group, which is mainly produced by fungi, is used as a biobased platform chemical and shows distinctive bioactivities. On the other hand, some fungi and lichens produce itaconic acid derivatives possessing itaconic acid skeleton, and the number of the derivatives is currently more than seventy. Based on the molecular structures, they can be categorized into two groups, alkylitaconic acids and α-methylene-γ-butyrolactones. Interestingly, some itaconic acid derivatives show versatile functions such as antimicrobial, anti-inflammatory, antitumor, and plant growth-regulating activities. The vinylidene group of itaconic acid derivatives likely participates in these functions. It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first biosynthesized from acyl-CoA and oxaloacetic acid. Some modifying enzymes such as hydroxylase and dehydratase are likely involved in the further modification after biosynthesis of their precursors. This contributes to the diversity of itaconic acid derivatives. In this review, we summarize their structures, functions, and biosynthetic pathways together with a discussion of a strategy for the industrial use. KEY POINTS: • Itaconic acid derivatives can be categorized into alkylitaconic acids and α-methylene-γ-butyrolactones. • The vinylidene group of itaconic acid derivatives likely participates in their versatile function. • It is suggested that α-methylene-γ-butyrolactones are biosynthesized from alkylitaconic acids which are first synthesized from acyl-CoA and oxaloacetic acid.

Biobased Poly(itaconic Acid-co-10-Hydroxyhexylitaconic Acid)s: Synthesis and Thermal Characterization

Renewable vinyl compounds itaconic acid (IA) and its derivative 10-hydroxyhexylitaconic acid (10-HHIA) are naturally produced by fungi from biomass. This provides the opportunity to develop new biobased polyvinyls from IA and 10-HHIA monomers. In this study, we copolymerized these monomers at different ratios through free radical aqueous polymerization with potassium peroxodisulfate as an initiator, resulting in poly(IA-co-10-HHIA)s with different monomer compositions. We characterized the thermal properties of the polymers by thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FT-IR). The nuclear magnetic resonance analysis and the gel permeation chromatography showed that the polymerization conversion, yield, and the molecular weights (weight-averaged Mw and number-averaged Mn) of the synthesized poly(IA-co-10-HHIA)s decreased with increasing 10-HHIA content. It is suggested that the hydroxyhexyl group of 10-HHIA inhibited the polymerization. The TGA results indicated that the poly(IA-co-10-HHIA)s continuously decomposed as temperature increased. The FT-IR analysis suggested that the formation of the hydrogen bonds between the carboxyl groups of IA and 10-HHIA in the polymer chains was promoted by heating and consequently the polymer dehydration occurred. To the best of our knowledge, this is the first time that biobased polyvinyls were synthesized using naturally occurring IA derivatives.

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

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.

A high-throughput screening method based on the Mizoroki-Heck reaction for isolating itaconic acid-producing fungi from soils

In this study, we report a novel method based on the Mizoroki-Heck reaction followed by an iodine test for the screening of itaconic acid-producing fungi from soils. This method is simple, rapid, and requires 10 μL of culture; results are obtained within 1.5 h. The detection limit of itaconic acid in the cultures was 0.13 mM. This is the first report on the direct screening of itaconic acid-producing fungi using a coupling reaction.

Challenges in the production of itaconic acid by metabolically engineered Escherichia coli

Metabolic engineering allows the production of a variety of high-value chemicals in heterologous hosts. For example, itaconic acid (IA) has been produced in several microorganisms, such as Escherichia coli, Aspergillus niger, and Synechocystis sp. through the expression of cis-aconitate decarboxylase gene (cad) from Aspergillus terreus. Recently, we showed that inactivation of the isocitrate dehydrogenase gene and overexpression of the aconitase gene dramatically enhanced the production levels of IA in E. coli expressing cad. Furthermore, we demonstrated that it is possible to produce IA directly from starch by engineered E. coli that additionally expresses the α-amylase gene from Streptococcus bovis. In this study, we sum up our findings regarding the challenges of IA production in E. coli.