MMR_2024v14n3

Molecular Microbiology Research 2024, Vol.14, No.3, 141-152 http://microbescipublisher.com/index.php/mmr 144 Both A. oryzae and A. flavus exhibit filamentous growth and produce conidia. However, A. flavus conidia are typically rougher and more variable in shape compared to the smooth, spherical conidia of A. oryzae. This morphological distinction is significant in industrial settings where the purity and consistency of fungal cultures are essential (Zhang et al., 2015). Furthermore, A. oryzae is non-toxigenic and safe for food production, while A. flavus produces aflatoxins, which are potent carcinogens posing significant health risks. Comparing A. oryzae with Aspergillus niger reveals notable differences in enzymatic activity and industrial applications. Both species are prolific producers of hydrolytic enzymes. A. niger is particularly noted for its production of citric acid and pectinases, whereas A. oryzae is renowned for its amylases and proteases (Park et al., 2019). Additionally, A. niger typically forms black or dark conidia, whereas A. oryzae produces green to yellow conidia. These color and morphology differences are useful for distinguishing between the two species in industrial applications. The metabolic pathways of A. oryzae andA. niger differ, with A. niger exhibiting a broader range of organic acid production, including high levels of citric acid. This makes A. niger a primary organism for industrial citric acid production, whereas A. oryzae excels in producing enzymes critical for fermenting starch-based substrates (Daba et al., 2021). 3 Mechanisms of Action in Pest Control 3.1Antifungal properties and inhibition of fungal pathogens Aspergillus oryzae demonstrates significant antifungal properties, making it a promising candidate for biological control against fungal pathogens affecting rice. Studies have shown that certain strains of A. oryzae can inhibit the growth of various pathogenic fungi. For example, the strain Aspergillus oryzae 18HG80, isolated from saline soil, exhibited notable antifungal activity against phytopathogens such as Aspergillus flavus, Fusarium oxysporum, and Alternaria solani. The strain inhibited their growth with varying degrees of effectiveness, showing the highest inhibition against A. flavus andF. oxysporum(Nacef et al., 2020). The mechanism behind this antifungal activity involves the production of secondary metabolites such as kojic acid and butanedioic acid. These compounds interfere with the cellular processes of the target fungi, leading to inhibited growth and reduced pathogenicity. Additionally, environmental factors such as temperature and pH were found to influence the antifungal activity of A. oryzae, with optimal activity observed at 30 ℃ and pH 6 (Nacef et al., 2020). Further research demonstrated that essential oils and other bioactive compounds derived fromA. oryzae could be effective in controlling fungal pathogens in agricultural settings. For instance, studies have shown that essential oils with antifungal properties significantly inhibit the growth of Aspergillus oryzae, suggesting potential applications in the preservation of cultural relics and possibly in crop protection. 3.2 Antibacterial activity against rice pathogens In addition to its antifungal properties, Aspergillus oryzae also exhibits antibacterial activity against several rice pathogens. This antibacterial potential is particularly significant in controlling diseases caused by bacterial pathogens such as Xanthomonas oryzae pv. oryzae, which is responsible for bacterial leaf blight in rice. Research has identified strains of A. oryzae that produce metabolites with strong antibacterial effects. Jiang et al. (2019) highlighted the isolation of Aspergillus sclerotiorum strain As-75, which demonstrated significant antagonistic activity against X. oryzae pv. oryzae. The strain produced a novel compound identified as (2Z)-2-butenedioic acid-2-(1-methylethenyl)-4-methyl ester, which showed strong antibacterial activity and improved control efficiency in preventing rice bacterial blight (Jiang et al., 2019). Moreover, Shoji et al. (2021) discovered a novel water extract from rice fermented with Aspergillus oryzae and Saccharomyces cerevisiae, suggesting broader antimicrobial potential. The extract promoted cell survival and inhibited viral infection, indicating that A. oryzae can produce bioactive compounds with diverse antimicrobial properties (Shoji et al., 2021).

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