Production of labyrinthopeptin A1 with Actinomadura namibiensis

The filamentous actinomycete Actinomadura namibiensis is the only known producer of labyrinthopeptins, a class of ribosomally synthesized and posttranslationally modified peptides (RiPPs) displaying highly attractive bioactive properties. In order to increase the labyrinthopeptin A1 productivity in shaking flask cultivations of A. namibiensis, a new cultivation method called salt-enhanced cultivation was used. Compared to the unsupplemented control, labyrinthopeptin A1 productivity was enhanced the most by addition of 50 mM (NH4)2SO4, reaching a 7-fold higher yield of 325 mg L-1 within 10 cultivation days. Salt-enhanced cultivation affected growth and product formation mechanisms, cell morphology characteristics and rheological characteristics of cultivation broth. An image analysis method was developed to quantify both the macro-morphology (pellet size and shape) and the micro-morphology (hyphal network structure) of the heterogeneous filamentous biomass in detail. Productivity-related morphological parameters were in particular the size and circularity of pellets and the degree of hyphal interweaving (hyphal network spacing). It was shown that the time-dependent change in morphology linked to the rheological properties of the cultivation broth. The results presented in this work provide new insights into the cultivation aspects of A. namibiensis and illustrate the challenges on the way to a comprehensive understanding of the complex relationship between productivity, morphology and rheology in filamentous cultivations.