Roy Keya Rani, Byrd Zachary, Sama Michael P, Barzee Tyler J
Department of Biosystems and Agricultural Engineering, University of Kentucky, Lexington, KY, 40506, USA.
Fungal Biol Biotechnol. 2025 Jun 4;12(1):10. doi: 10.1186/s40694-025-00202-y.
Stillage is a byproduct of distilleries which is rich in organic matter, minerals, and acidic components. It is commonly used as animal feed and has high potential for use as an alternative substrate for microorganisms. Filamentous fungi are saprophytes that can utilize stillage solids to grow as threadlike mycelium. The structure and composition of the filamentous mycelium has shown promise to produce pure mycelium materials (PMM), which might have potential to serve as leather-like or other novel materials with improved environmental impact profiles. Basidiomycota fungi (including true mushrooms) species are presently used in industry to produce PMM due to the ease of suppressing sporulation and encouraging vegetative growth. Other fungal phyla such as Mucoromycota offer benefits of faster growth, but suppression of sporulation is often more difficult. The production of PMM is a relatively new area and sufficient quantitative data is lacking on the effective cultivation and processing steps required to optimize the materials for different potential applications. In this study, a cultivation system capable of producing PMM with solid-state fermentation (SSF) of stillage substrate by Mucoromycota fungus Rhizopus microsporus var. oligosporus was designed and tested. The influence of important operational parameters on the aerial mycelium growth characteristics was studied including (1) substrate packing density, (2) external support geometry, (3) substrate carbon-to-nitrogen (C: N) ratio, and (4) aerial delivery of additives. The results showed that stillage was a favorable substrate to produce PMM and that the studied operational parameters allowed for effective control of the mycelium fiber length, density, and moisture content. R. oligosporus displayed rapid growth, enhanced 3 to 4 times compared to Basidiomycota fungus Pleurotus ostreatus (oyster mushroom). Increasing substrate packing density and the length of external supports was found to encourage development of longer aerial mycelium fibers while aerial delivery of additives was found to have limited effects on fiber length but significantly influenced mycelium density and moisture content. It was also found that the use of unprocessed stillage solids was effective at delaying the sporulation of this Mucoromycota fungus and promoting development of aerial mycelium, which was hypothesized to be related to its natively low C: N ratio. Together, these results indicate promise for the efficient production of tunable PMM from inexpensive organic substrates.
酒糟是酿酒厂的一种副产品，富含有机物、矿物质和酸性成分。它通常用作动物饲料，并且作为微生物的替代底物具有很高的利用潜力。丝状真菌是腐生菌，能够利用酒糟固体生长成丝状菌丝体。丝状菌丝体的结构和组成已显示出有望生产纯菌丝体材料（PMM），这种材料可能有潜力用作类似皮革的材料或其他对环境影响较小的新型材料。担子菌门真菌（包括真蘑菇）目前在工业上用于生产PMM，因为易于抑制孢子形成并促进营养生长。其他真菌门，如毛霉门，具有生长更快的优势，但抑制孢子形成通常更困难。PMM的生产是一个相对较新的领域，缺乏足够的定量数据来了解优化不同潜在应用材料所需的有效培养和加工步骤。在本研究中，设计并测试了一种能够通过米根霉（Rhizopus microsporus var. oligosporus）对酒糟底物进行固态发酵（SSF）来生产PMM的培养系统。研究了重要操作参数对气生菌丝生长特性的影响，包括（1）底物堆积密度、（2）外部支撑物几何形状、（3）底物碳氮比（C:N）以及（（4）添加剂的气送。结果表明，酒糟是生产PMM的良好底物，所研究的操作参数能够有效控制菌丝纤维长度、密度和水分含量。米根霉生长迅速，与担子菌门真菌糙皮侧耳（Pleurotus ostreatus，平菇）相比，生长速度提高了3至4倍。发现增加底物堆积密度和外部支撑物长度可促进更长气生菌丝纤维的发育，而添加剂的气送对纤维长度影响有限，但显著影响菌丝密度和水分含量。还发现使用未加工的酒糟固体可有效延迟这种毛霉门真菌的孢子形成并促进气生菌丝的发育，据推测这与其天然较低的C:N比有关。总之，这些结果表明从廉价有机底物高效生产可调谐PMM具有前景。
