Fig. 3.

Formation of S-cells is widespread in filamentous actinomycetes. a Morphology of S-cells released by K. viridifaciens, S. venezuelae and a number of filamentous actinomycetes from our culture collection (all referred to with the prefix MBT). Cells were stained with FM5-95 (red) and SYTO-9 (green) to visualize membranes and DNA, respectively. b Phylogenetic tree of filamentous actinomycetes based on the taxonomic marker ssgB. Strains with the ability to form S-cells are indicated with an asterisk (*). Streptomyces strains that are able to produce spores in liquid-grown cultures are referred to as LSp (for Liquid Sporulation), while those unable to sporulate in liquid environments are called NLSp (No Liquid Sporulation²⁶). This classification is based on amino acid residue 128 in the conserved SsgB protein, which is a threonine (T) or glutamine (Q) for LSp and NLSp strains, respectively. Please note that an arginine (R) is present at this position in all Kitasatospora strains (c). Scale bars represent 5 µm