Challenges of influencing cellular morphology by morphology engineering techniques and mechanical induced stress on filamentous pellet systems : a critical review

Filamentous microorganisms are main producers of organic acids, enzymes, and pharmaceutical agents such as antibiotics and other active pharmaceutical ingredients. With their complex cell morphology, ranging from dispersed mycelia to dense pellets, the cultivation is challenging. In recent years, various techniques for tailor‐made cell morphologies of filamentous microorganisms have been developed to increase product formation and have been summarised under the term morphology engineering. These techniques, namely microparticle‐enhanced cultivation, macroparticle‐enhanced cultivation, and alteration of the osmolality of the culture medium by addition of inorganic salts, the salt‐enhanced cultivation, are presented and discussed in this review. These techniques have already proven to be useful and now await further proof‐of‐concept. Furthermore, the mechanical behaviour of individual pellets is of special interest for a general understanding of pellet mechanics and the productivity of biotechnological processes with filamentous microorganisms. Correlating them with substrate uptake and finally with productivity would be a breakthrough not to be underestimated for the comprehensive characterisation of filamentous systems. So far, this research field is under‐represented. First results on filamentous pellet mechanics are discussed and important future aspects, which the filamentous expert community should deal with, will be presented and critically discussed.