Consistent production of kojic acid from Aspergillus sojae SSC-3 isolated from rice husk

Functional role of a novel zinc finger protein, AoZFA, in growth and kojic acid synthesis in Aspergillus oryzae

Kojic acid (KA) is a valuable secondary metabolite that is regulated by zinc finger proteins in Aspergillus oryzae. However, only two such proteins have been characterized to function in kojic acid production of A. oryzae to date. In this study, we identified a novel zinc finger protein, AoZFA, required for kojic acid biosynthesis in A. oryzae. Our results showed that disruption of AozfA led to increased expression of kojA and kojR involved in kojic acid synthesis, resulting in enhanced kojic acid production, while overexpression of AozfA had the opposite effect. Furthermore, deletion of kojR in the AozfA disruption strain abolished kojic acid production, whereas overexpression of kojR enhanced it, indicating that AoZFA regulates kojic acid production by affecting kojR. Transcriptional activation assay revealed that AoZFA is a transcriptional activator. Interestingly, when kojR was overexpressed in the AozfA overexpression strain, the production of kojic acid failed to be rescued, suggesting that AozfA plays a distinct role from kojR in kojic acid biosynthesis. Moreover, we found that AozfA was highly induced by zinc during early growth stages, and its overexpression inhibited the growth promoted by zinc, whereas its deletion had no effect, suggesting that AoZFA is non-essential but has a role in the response of A. oryzae to zinc. Overall, these findings provide new insights into the roles of zinc finger proteins in the growth and kojic acid production of A. oryzae.IMPORTANCEKojic acid (KA) is an economically valuable secondary metabolite produced by Aspergillus oryzae due to its vast biological activities. Genetic modification of A. oryzae has emerged as an efficient strategy for enhancing kojic acid production, which is dependent on the mining of genes involved in kojic acid synthesis. In this study, we have characterized a novel zinc-finger protein, AoZFA, as a negative regulator of kojic acid production by affecting kojR. AozfA is an excellent target for improving kojic acid production without any effects on the growth of A. oryzae. Furthermore, the simultaneous modification of AozfA and kojR exerts a more significant promotional effect on kojic acid production than the modification of single genes. This study provides new insights for the regulatory mechanism of zinc finger proteins in the growth and kojic acid production of A. oryzae.

Fungal production of kojic acid and its industrial applications

Kojic acid has gained its importance after it was known worldwide that the substance functions primarily as skin-lightening agent. Kojic acid plays a vital role in skin care products, as it enhances the ability to prevent exposure to UV radiation. It inhibits the tyrosinase formation which suppresses hyperpigmentation in human skin. Besides cosmetics, kojic acid is also greatly used in food, agriculture, and pharmaceuticals industries. Conversely, according to Global Industry Analysts, the Middle East, Asia, and in Africa especially, the demand of whitening cream is very high, and probably the market will reach to $31.2 billion by 2024 from $17.9 billion of 2017. The important kojic acid-producing strains were mainly belongs to the genus Aspergillus and Penicillium. Due to its commercial potential, it continues to attract the attention for its green synthesis, and the studies are still widely conducted to improve kojic acid production. Thus, the present review is focused on the current production processes, gene regulation, and limitation of its commercial production, probable reasons, and possible solutions. For the first time, detailed information on the metabolic pathway and the genes involved in kojic acid production, along with illustrations of genes, are highlighted in the present review. Demand and market applications of kojic acid and its regulatory approvals for its safer use are also discussed. KEY POINTS: • Kojic acid is an organic acid that is primarily produced by Aspergillus species. • It is mainly used in the field of health care and cosmetic industries. • Kojic acid and its derivatives seem to be safe molecules for human use.

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.

Morphologically dissimilar spores of Aspergillus sojae exhibit genomic homogeneity but the differential in Kojic acid accumulation

We reported that Aspergillus sojae (SSC-3), an indigenous isolate from rice husk, is a potent kojic acid producer. During optimization, it was observed that under static fermentation conditions, this fungal strain produces two dissimilar morphological green and yellow spores, i.e., SSC-3(Y) and SSC-3(G). Furthermore, these different spore types differ in color, morphology, and in kojic acid metabolite accumulation, with green spores producing 12.87 g/l and yellow spores producing 8.63 g/l of kojic acid on the 12th day of fermentation. To understand if there is a genetic basis for the difference in morphology and metabolite accumulation characteristics, sequencing of internal transcribed spacer regions (ITS) and RAPD analysis from both the spore were carried out. Our study revealed that though the spores are dissimilar with respect to morphology and metabolite accumulation profile, they are genetically homogenous. This suggests that there could be epigenetic differences in these spore types, which may be explored in detail in further studies.

Review on the Use of Kojic Acid—A Skin-Lightening Ingredient

This article reviews the use of Kojic Acid (KA) as a skin-lightening ingredient in the cosmetics industry. In 1907, Saito discovered KA, a natural product; it has since become one of the most investigated skin-lightening agents. This paper highlights the findings of the research conducted on this agent. It has been found that KA has certain disadvantages, and researchers have attempted to mitigate these disadvantages by designing new equivalents of KA that are more efficient in tyrosinase inhibition. These equivalents are also safe to use and have improved properties and solubility. The Cosmeceutical Ingredient Review (CIR) indicates that this ingredient can be safely used at a concentration not higher than 1% due to its cytotoxicity. Other scientific data also support its safety at a concentration of 2% or less. It was shown to be helpful in the treatment of hyper pigmentary disorders, such as freckles, age spots, post-inflammatory hyperpigmentation, and melasma, which has been proven clinically.

In vitro cosmeceutical activity of alcoholic extract from chestnut inner shell fermented with Aspergillus sojae

Chestnut inner shell was fermented in solid state with Aspergillus sojae, and then extracted using ethanol (95%) to analyze its cosmeceutical activity and phenolic composition. The fermentation significantly increased the antioxidant activity, and in vitro cosmeceutical activities. The ethanol extract showed the higher activities than ethyl acetate and water extracts. DPPH radical scavenging activity of the alcoholic extract was 80.53%, and tyrosinase and elastase inhibition activities were 101.01%, and 76.73%, respectively, after 10 days of fermentation. Kojic acid, a secondary metabolite of A. sojae was produced by the fermentation as a major bioactive component. Gallic acid, ellagic acid, and coumaric acid appeared the major phenolic acids in the alcoholic extract from fermented chestnut inner shell. The alcoholic extract from chestnut inner shell fermented by A. sojae may be used as an effective and bioactive cosmeceutical.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01044-9.

Emerging mycotoxins in infant and children foods: A review

A proper nutrition is crucial for children's healthy development. Regardless of the usual recommendations to follow a varied diet, some foods can be a source of toxic natural contaminants such as mycotoxins, potent secondary metabolites produced by filamentous fungi. In addition to the most well-known mycotoxins, many of which are subject to tight regulation regarding the maximum levels allowed in different types of food, there is a large group of mycotoxins, the so-called emerging mycotoxins, about which less knowledge has already been acquired, which have gradually been the target of interest from the scientific community due to their prevalence in most foodstuffs, particularly in cereals and cereal-based products. Alternariol and his metabolite alternariol mono-methyl ether, beauvericin, citrinin, culmorin, enniatins, ergot alkaloids, fusaproliferin, kojic acid, moniliformin, sterigmatocystin, tentoxin and tenuazonic acid are the most representative of them. The current review gathered the information of the last ten years that have been published on the levels of emerging mycotoxins in food products dedicated for infants and children. European Union countries are responsible for most of the reported studies, which showed levels that can reach hundreds of mg/kg.