Abstract
Rhizopus oryzae (R. oryzae) can effectively produce organic acids, and its pellet formation in seed cultures has been shown to significantly enhance subsequent fermentation processes. Despite advances in strain development, simple and effective methods for inducing pellet morphology and a basic understanding of the mechanisms controlling this process could facilitate substantial increases in efficiency and product output. Here, we report that 1.5% triethanolamine (TEOA) in seed culture medium can activate the growth of R. oryzae spores in compact and uniform pellets which is optimal for fermentation conditions. Analysis of fermentation kinetics showed that the production of fumaric and L-malic acid increases 293% and 177%, respectively. Transcriptomic analysis revealed that exposure of R. oryzae to 1.5% TEOA during the seed culture activated the phosphatidylinositol and mitogen-activated protein kinase signaling pathways. Theses pathways subsequently stimulated the downstream carbohydrate-active synthases and hydrolases that required for cell wall component synthesis and reconstruction. Our results thus provide insight into the regulatory pathways controlling pellet morphology germane to the viability of seed cultures, and provide valuable reference data for subsequent optimization of organic acid fermentation by R. oryzae.
Highlights
Depletion of fossil fuel resources combined with excessive CO2 emissions has resulted in a growing environmental and energy crisis
Effects of different surfactants on the seed morphology of R. oryzae We first chose six surfactants, Triton 100, Tween 80, Tween 20, diethanolamine, ethanolamine, and trietha‐ nolamine (TEOA) as candidate additives to assess their respective effects on R. oryzae morphology in seed medium
In order to thoroughly analyze the molecular mechanism regarding to seed pellet formation, we chose the unmutagenized R. oryzae strain as a test object
Summary
Depletion of fossil fuel resources combined with excessive CO2 emissions has resulted in a growing environmental and energy crisis. The field of biorefinery aims to use microorganisms to convert renewable biomass into chemicals, fuels, and materials, offering a promising route to address these challenges [1, 2]. Among the microorganisms used in biorefinery processes, filamentous fungi occupy a uniquely favorable position due to their characteristically rapid propagation, high biomass density, and broad substrate range [3, 4]. Iyyappan et al showed that careful adjustment of the composition of the seed medium, spore inoculum concentration, and shaking speed can help optimize the pellet morphology of Aspergillus niger for the production of L-malic acid from glycerol [15]. Kurakake et al found that the mycelial pellets of Aspergillus oryzae became smaller and spherical following the addition of nonionic surfactants, resulting in enhanced production of β-fructofuranosidase [16]. Gao et al demonstrated that the morphology of the oleaginous fungus Mortierella isabellina could be precisely controlled by adding magnesium silicate microparticles [17]
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