Kojic acid production in an airlift bioreactor using partially hydrolyzed raw corn starch

Challenges and advancements in bioprocess intensification of fungal secondary metabolite: kojic acid

Kojic acid is a fungal secondary metabolite commonly known as a tyrosinase inhibitor, that acts as a skin-whitening agent. Its applications are widely distributed in the area of cosmetics, medicine, food, and chemical synthesis. Renewable resources are the alternative feedstocks that can fulfill the demand for free sugars which are fermented for the production of kojic acid. This review highlights the current progress and importance of bioprocessing of kojic acid from various types of competitive and non-competitive renewable feedstocks. The bioprocessing advancements, secondary metabolic pathway networks, gene clusters and regulations, strain improvement, and process design have also been discussed. The importance of nitrogen sources, amino acids, ions, agitation, and pH has been summarized. Two fungal species Aspergillus flavus and Aspergillus oryzae are found to be extensively studied for kojic acid production due to their versatile substrate utilization and high titer ability. The potential of A. flavus to be a competitive industrial strain for large-scale production of kojic acid has been studied.

Aspergillus oryzae-based cell factory for direct kojic acid production from cellulose

Background

Kojic acid (5-Hydroxy-2-(hydroxymethyl)-4-pyrone) is one of the major secondary metabolites in Aspergillus oryzae. It is widely used in food, pharmaceuticals, and cosmetics. The production cost, however, is too high for its use in many applications. Thus, an efficient and cost-effective kojic acid production process would be valuable. However, little is known about the complete set of genes for kojic acid production. Currently, kojic acid is produced from glucose. The efficient production of kojic acid using cellulose as an inexpensive substrate would help establish cost-effective kojic acid production.

Results

A kojic acid transcription factor gene over-expressing the A. oryzae strain was constructed. Three genes related to kojic acid production in this strain were transcribed in higher amounts than those found in the wild-type strain. This strain produced 26.4 g/L kojic acid from 80 g/L glucose. Furthermore, this strain was transformed with plasmid harboring 3 cellulase genes. The resultant A. oryzae strain successfully produced 0.18 g/L of kojic acid in 6 days of fermentation from the phosphoric acid swollen cellulose.

Conclusions

Kojic acid was produced directly from cellulose material using genetically engineered A. oryzae. Because A. oryzae has efficient protein secretion ability and secondary metabolite productivity, an A. oryzae-based cell factory could be a platform for the production of various kinds of bio-based chemicals.

Kojic Acid production from agro-industrial by-products using fungi

A total of 278 different isolates of filamentous fungi were screened using synthetic medium for respective ability to produce kojic acid. Nineteen, six, and five isolates proved to be low, moderate, and high kojic acid producers, respectively. Levels of kojic acid produced were generally increased when shaking cultivation was used rather than those obtained using static cultivation. A trial for the utilization of 15 agro-industrial wastes or by-products for kojic acid production by the five selected higher kojic acid producer isolates was made. The best by-product medium recorded was molasses for kojic acid. A. flavus numbers 7 and 24 were able to grow and produce kojic acid on only 12 out of 15 wastes or by-products media. The best medium used for kojic acid production by A. flavus number 7 was rice fragments followed by molasses, while the best medium used for kojic acid production by A. flavus number 24 was the molasses followed by orange, pea, and rice fragments. An attempt for production of kojic acid using a 1.5 L laboratory fermentor has been made. Aspergillus flavus number 7 was used and grown on molasses medium; maximum level (53.5 g/L) of kojic acid was obtained after eight days of incubation.

MIDDAS-M: motif-independent de novo detection of secondary metabolite gene clusters through the integration of genome sequencing and transcriptome data

Many bioactive natural products are produced as “secondary metabolites” by plants, bacteria, and fungi. During the middle of the 20th century, several secondary metabolites from fungi revolutionized the pharmaceutical industry, for example, penicillin, lovastatin, and cyclosporine. They are generally biosynthesized by enzymes encoded by clusters of coordinately regulated genes, and several motif-based methods have been developed to detect secondary metabolite biosynthetic (SMB) gene clusters using the sequence information of typical SMB core genes such as polyketide synthases (PKS) and non-ribosomal peptide synthetases (NRPS). However, no detection method exists for SMB gene clusters that are functional and do not include core SMB genes at present. To advance the exploration of SMB gene clusters, especially those without known core genes, we developed MIDDAS-M, a motif-independent de novodetection algorithm for SMB gene clusters. We integrated virtual gene cluster generation in an annotated genome sequence with highly sensitive scoring of the cooperative transcriptional regulation of cluster member genes. MIDDAS-M accurately predicted 38 SMB gene clusters that have been experimentally confirmed and/or predicted by other motif-based methods in 3 fungal strains. MIDDAS-M further identified a new SMB gene cluster for ustiloxin B, which was experimentally validated. Sequence analysis of the cluster genes indicated a novel mechanism for peptide biosynthesis independent of NRPS. Because it is fully computational and independent of empirical knowledge about SMB core genes, MIDDAS-M allows a large-scale, comprehensive analysis of SMB gene clusters, including those with novel biosynthetic mechanisms that do not contain any functionally characterized genes.

Identification and characterization of genes responsible for biosynthesis of kojic acid, an industrially important compound from Aspergillus oryzae

Kojic acid is produced in large amounts by Aspergillus oryzae as a secondary metabolite and is widely used in the cosmetic industry. Glucose can be converted to kojic acid, perhaps by only a few steps, but no genes for the conversion have thus far been revealed. Using a DNA microarray, gene expression profiles under three pairs of conditions significantly affecting kojic acid production were compared. All genes were ranked using an index parameter reflecting both high amounts of transcription and a high induction ratio under producing conditions. After disruption of nine candidate genes selected from the top of the list, two genes of unknown function were found to be responsible for kojic acid biosynthesis, one having an oxidoreductase motif and the other a transporter motif. These two genes are closely associated in the genome, showing typical characteristics of genes involved in secondary metabolism.

Filamentous fungi for production of food additives and processing aids

Filamentous fungi are metabolically versatile organisms with a very wide distribution in nature. They exist in association with other species, e.g. as lichens or mycorrhiza, as pathogens of animals and plants or as free-living species. Many are regarded as nature's primary degraders because they secrete a wide variety of hydrolytic enzymes that degrade waste organic materials. Many species produce secondary metabolites such as polyketides or peptides and an increasing range of fungal species is exploited commercially as sources of enzymes and metabolites for food or pharmaceutical applications. The recent availability of fungal genome sequences has provided a major opportunity to explore and further exploit fungi as sources of enzymes and metabolites. In this review chapter we focus on the use of fungi in the production of food additives but take a largely pre-genomic, albeit a mainly molecular, view of the topic.