Genomics of Aspergillus oryzae: Learning from the History of Koji Mold and Exploration of Its Future

Abstract

At a time when the notion of microorganisms did not exist, our ancestors empirically established methods for the production of various fermentation foods: miso (bean curd seasoning) and shoyu (soy sauce), both of which have been widely used and are essential for Japanese cooking, and sake, a magical alcoholic drink consumed at a variety of ritual occasions, are typical examples. A filamentous fungus, Aspergillus oryzae, is the key organism in the production of all these traditional foods, and its solid-state cultivation (SSC) has been confirmed to be the secret for the high productivity of secretory hydrolases vital for the fermentation process. Indeed, our genome comparison and transcriptome analysis uncovered mechanisms for effective degradation of raw materials in SSC: the extracellular hydrolase genes that have been found only in the A. oryzae genome but not in A. fumigatus are highly induced during SSC but not in liquid cultivation. Also, the temperature reduction process empirically adopted in the traditional soy-sauce fermentation processes has been found to be important to keep strong expression of the A. oryzae-specific extracellular hydrolases. One of the prominent potentials of A. oryzae is that it has been successfully applied to effective degradation of biodegradable plastic. Both cutinase, responsible for the degradation of plastic, and hydrophobin, which recruits cutinase on the hydrophobic surface to enhance degradation, have been discovered in A. oryzae. Genomic analysis in concert with traditional knowledge and technology will continue to be powerful tools in the future exploration of A. oryzae.

Bioethanol Production from Brewers Spent Grains Using a Fungal Consolidated Bioprocessing (CBP) Approach

“…Operation of the sake-based CBP system at a lower solids loading (lower solid to liquid ratio) or the use of stirred or mixed fermentation vessels could possibly result in higher ethanol yields, by increasing successful enzyme-substrate interactions. Paradoxically, however, enzyme secretion has been shown to be greater on solid-state cultures as compared with highly dilute liquid cultures [27]. This could perhaps relate to a starvation response, as seen in biofilm formation.…”

“…That this was not the case once again suggests that the enzyme concentration was not the rate-limiting factor in these fermentations. It has previously been reported that temperature reduction can play a role in maintaining continued expression of extracellular hydrolases when using A. oryzae in a solid-state cultivation system for the traditional manufacture of products such as soy sauce [27]. The hypothesis, which may help to explain the results observed here, is that reduced mobility of the secreted enzymes in solid-state cultures at lower temperatures may significantly reduce product feedback inhibition of the expression of hydrolases, therefore resulting in higher secreted enzyme concentrations.…”

“…A. oryzae has both cutinase (CutL1) and hydrophobin genes (such as rolA) within its genome which have been shown to be responsible for the deconstructive mechanism. Cutinase facilitates the actual decomposition of the plastic, with hydrophobins acting as 'scaffolding' for the specific site recruitment of the cutinase onto the hydrophobic surfaces of biodegradable plastics [27,35].…”

<i>Aspergillus Oryzae</i> Strain with Improved Conidiation after Light Stimulation

“…We analyzed the homologues of nine up-regulated genes, a neutral gene (laeA), and a down-regulated gene (veA) as reported in A. nidulans (Ruger-Herreros et al 2011). In the A. nidulans study, the most up-regulated gene (ccgB) and second most up-regulated gene (ccgA) (RugerHerreros et al 2011), which are homologues of the N. crassa ccg-1 gene, a clock-controlled and glucose-repressed gene of unknown function (Arpaia et al 1995), were not found in the A. oryzae genome (Machida et al 2008). We conducted RT-PCR on nine of the 11 genes described above, excluding ccgA and ccgB.…”

Advances in consolidated bioprocessing systems for bioethanol and butanol production from biomass: a comprehensive review

“…oryzae is a fungus with high potential for the secretory production of various enzymes and is commonly used in traditional Japanese fermentation industries (Machida et al, 2008). Recently, Hossain (2013) reported the optimization of direct ethanol production using A. oryzae from non-pretreated and pre-treated corn stover in a continuous stirred batch bioreactor.…”