Rheology and Culture Reproducibility of Filamentous Microorganisms: Impact of Flow Behavior and Oxygen Transfer During Salt-Enhanced Cultivation of the Actinomycete Actinomadura namibiensis

Abstract

Analyzing the relationship between cell morphology, rheological characteristics, and production dynamics of cultivations with filamentous microorganisms is a challenging task. The complex interdependencies and the commonly low reproducibility of heterogeneous cultivations hinder the bioprocess development of commercially relevant production systems. The present study aims to characterize process parameters in Actinomadura namibiensis shake flask cultures to gain insights into relationships between culture behavior and rheological characteristics during salt-enhanced labyrinthopeptin A1 production. Plate–plate (PP) and vane–cup rheometer measurements of viscous model fluids and culture broths are compared, revealing a more uniform distribution of broth when measured with the PP system. Additionally, rheological characteristics and culture performance of A. namibiensis cultures are evaluated using online data of the specific power input and the oxygen transfer rate. It is demonstrated that salt-enhancement labyrinthopeptin A1 production by the addition of 50 mM (NH₄)₂SO₄ increases the apparent viscosity of the A. namibiensis culture by four-fold and significantly reduces the reproducibility of the culture resulting in a 46 h difference in lag-phase duration. This approach demonstrates that the culture behavior of complex filamentous cell morphologies is challenging to decipher, but online monitoring of rheology and oxygen transfer can provide valuable insights into the cultivation dynamics of filamentous microbial cultures.