Serrano-Carreón L, Galindo E, Rocha-Valadéz J A, Holguín-Salas A, Corkidi G
Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, 62210, Cuernavaca, Mor, México,
Adv Biochem Eng Biotechnol. 2015;149:55-90. doi: 10.1007/10_2015_304.
Filamentous cultures, such as fungi and actinomycetes, contribute substantially to the pharmaceutical industry and to enzyme production, with an annual market of about 6 billion dollars. In mechanically stirred reactors, most frequently used in fermentation industry, microbial growth and metabolite productivity depend on complex interactions between hydrodynamics, oxygen transfer, and mycelial morphology. The dissipation of energy through mechanically stirring devices, either flasks or tanks, impacts both microbial growth through shearing forces on the cells and the transfer of mass and energy, improving the contact between phases (i.e., air bubbles and microorganisms) but also causing damage to the cells at high energy dissipation rates. Mechanical-induced signaling in the cells triggers the molecular responses to shear stress; however, the complete mechanism is not known. Volumetric power input and, more importantly, the energy dissipation/circulation function are the main parameters determining mycelial size, a phenomenon that can be explained by the interaction of mycelial aggregates and Kolmogorov eddies. The use of microparticles in fungal cultures is also a strategy to increase process productivity and reproducibility by controlling fungal morphology. In order to rigorously study the effects of hydrodynamics on the physiology of fungal microorganisms, it is necessary to rule out the possible associated effects of dissolved oxygen, something which has been reported scarcely. At the other hand, the processes of phase dispersion (including the suspended solid that is the filamentous biomass) are crucial in order to get an integral knowledge about biological and physicochemical interactions within the bioreactor. Digital image analysis is a powerful tool for getting relevant information in order to establish the mechanisms of mass transfer as well as to evaluate the viability of the mycelia. This review focuses on (a) the main characteristics of the two most common morphologies exhibited by filamentous microorganisms; (b) how hydrodynamic conditions affect morphology and physiology in filamentous cultures; and (c) techniques using digital image analysis to characterize the viability of filamentous microorganisms and mass transfer in multiphase dispersions. Representative case studies of fungi (Trichoderma harzianum and Pleurotus ostreatus) exhibiting different typical morphologies (disperse mycelia and pellets) are discussed.
丝状培养物，如真菌和放线菌，对制药行业和酶生产有重大贡献，年市场规模约为60亿美元。在发酵工业中最常用的机械搅拌反应器中，微生物生长和代谢产物生产力取决于流体动力学、氧气传递和菌丝形态之间的复杂相互作用。通过机械搅拌装置（无论是烧瓶还是罐体）进行的能量耗散，既通过对细胞的剪切力影响微生物生长，也影响质量和能量传递，改善了相（即气泡和微生物）之间的接触，但在高能量耗散率下也会对细胞造成损伤。细胞中的机械诱导信号引发对剪切应力的分子反应；然而，完整的机制尚不清楚。体积功率输入，更重要的是能量耗散/循环功能，是决定菌丝大小的主要参数，这一现象可以通过菌丝聚集体和柯尔莫哥洛夫涡旋的相互作用来解释。在真菌培养中使用微粒也是一种通过控制真菌形态来提高过程生产力和可重复性的策略。为了严格研究流体动力学对真菌微生物生理学的影响，有必要排除溶解氧可能的相关影响，而这方面的报道很少。另一方面，相分散过程（包括作为丝状生物质的悬浮固体）对于全面了解生物反应器内的生物和物理化学相互作用至关重要。数字图像分析是获取相关信息以建立传质机制以及评估菌丝活力的有力工具。本综述重点关注：（a）丝状微生物呈现的两种最常见形态的主要特征；（b）流体动力学条件如何影响丝状培养物的形态和生理学；（c）使用数字图像分析技术来表征丝状微生物的活力以及多相分散体系中的传质。讨论了表现出不同典型形态（分散菌丝体和菌球）的真菌（哈茨木霉和糙皮侧耳）的代表性案例研究。
