Morphology and productivity of filamentous fungi

Abstract

Cultivation processes involving filamentous fungi have been optimised for decades to obtain high product yields. Several bulk chemicals like citric acid and penicillin are produced this way. A simple adaptation of cultivation parameters for new production processes is not possible though. Models explaining the correlation between process-dependent growth behaviour and productivity are therefore necessary to prevent long-lasting empiric test series. Yet, filamentous growth consists of a complex microscopic differentiation process from conidia to hyphae resulting in various macroscopically visible appearances. Early approaches to model this morphologic development are recapitulated in this review to explain current trends in this area of research. Tailoring morphology by adjusting process parameters is one side of the coin, but an ideal morphology has not even been found. This article reviews several reasons for this fact starting with nutrient supply in a fungal culture and presents recent advances in the investigation of fungal metabolism. It illustrates the challenge to unfold the relationship between morphology and productivity.

Microparticle‐enhanced cultivation of filamentous microorganisms: Increased chloroperoxidase formation by Caldariomyces fumago as an example

“…The synthesis of these products is often dependent on the morphology of the microorganisms (Gibbs et al, 2000;Grimm et al, 2005). For instance, for enzyme production processes with Aspergillus species, dispersed mycelial suspensions are often favored over the pelleted form due to higher product yields obtained, despite the higher viscosities associated with the higher cell densities of dispersed mycelial cultures (Christiansen et al, 1998;Couri et al, 2003;Gibbs et al, 2000).…”

“…The specific morphology of filamentous microorganisms leads to the formation of mycelial clumps resulting in difficulties with mixing and limitations in oxygen and nutrient supply of the biomass (Gibbs et al, 2000;Grimm et al, 2005;Znidarsic and Pavko, 2001). These difficulties also reduce the capacity of C. fumago for growth and enzyme secretion.…”

“…The cultivation of filamentous fungi is often accompanied by technical problems, such as high broth viscosity, clumpy growth, insufficient oxygen, and nutrient transfer which results in reduced productivity or even inactivation predominantly of cells in the center of the pellets (Gibbs et al, 2000;Grimm et al, 2005;Huang and Bungay, 1973;Znidarsic and Pavko, 2001). Although pellet-like growth of fungi has been reported to be important or even a prerequisite for certain production processes, there is a general agreement that in most cases loosely grown mycelia lead to higher biomass concentrations and specific activities due to a better nutrient supply of cells in a dispersed mycelial culture (Couri et al, 2003;Elmayergi et al, 1973;Gibbs et al, 2000;Grimm et al, 2005).…”

“…Although pellet-like growth of fungi has been reported to be important or even a prerequisite for certain production processes, there is a general agreement that in most cases loosely grown mycelia lead to higher biomass concentrations and specific activities due to a better nutrient supply of cells in a dispersed mycelial culture (Couri et al, 2003;Elmayergi et al, 1973;Gibbs et al, 2000;Grimm et al, 2005). Depending on the species used and the cultivation parameters applied different mycelial morphologies appear during the cultivation of filamentous microorganisms.…”

Agitation effects on morphology and protein productive fractions of filamentous and pelleted growth forms of recombinant Aspergillus niger

“…Filamentous fungi such as A. niger exhibit different growth morphologies in submerged culture varying from compact pelleted to filamentous growth forms which strongly affect the overall cell performance [15]. An important advantage of the pelleted morphology is the decrease in viscosity of the culture fluid, resulting in improved mixing and mass transfer properties.…”