An image analysis method to quantify heterogeneous filamentous biomass based on pixel intensity values – Interrelation of macro- and micro-morphology in Actinomadura namibiensis

Abstract

• An image analysis method for the heterogeneous cell morphology was developed. • Quantification of the network of dispersed mycelia. • Salt-enhanced cultivation affected pellet size and non-agglomerated hyphal network. • Hyphal network spacing was found to decrease during salt-enhanced cultivation. • A new correlation between macro- and micro-morphological parameters was found. The cell morphology of the filamentous actinobacterium Actinomadura namibiensis was evaluated by image analysis of microscopic pictures. A pixel intensity thresholding method was used to differentiate between pelleted bioagglomerates, the macro-morphology, and the characterization of individual hyphae, the micro-morphology. At both scales morphological differences between salt-enhanced cultivation (addition of 50 mM (NH 4 ) 2 SO 4 ), which increased the labyrinthopeptin A1 concentration from < 50–325 mg L −1 , and the non-supplemented standard medium were revealed. The major focus in this investigation was set on the analysis of the network of dispersed mycelia to provide complementary data to previously published pellet shape characteristics. Hyphal network spacing (HNS), a newly introduced shape descriptor to describe the spatial proximity of loosely entangled hyphae, was found to decrease to during salt-enhanced cultivation resulting in a 20 % lower HNS value compared to the unsupplemented control after 10 d of shaking flask cultivation. The macro-morphological pellet shape descriptors of circularity and aspect ratio correlated with individual micro-morphological parameters. The strongest correlation was found between pellet circularity and hyphal growth unit (HGU) (r = 0.73) and between pellet circularity and HNS (r = 0.82).