Cell wall characteristics of Thielavia terrestris dispersed and pelleted mycelia

In submerged fermentation of filamentous fungi, pelleted and dispersed types of growth are the two main morphological forms largely affecting the productivity of industrial processes. Despite the immense importance of fungal biotechnology various aspects of the biology of these two growth forms have been rarely studied. Whether there are any differences in architecture and properties of hyphal cell wall between pelleted and dispersed mycelia of the same non-genetically modified fungus was unknown. This comparative study characterized the cell wall structure and properties of pelleted and dispersed forms of Thielavia terrestris growth. Infrared spectroscopy revealed that the hyphal cell wall of pellets, in contrast to dispersed mycelium, contained considerably more chitin (22 % and 1-2 % of dry weight [dw], respectively), glucans (28 % and 10 % dw), and lipids (8 % and 6 % dw). The dispersed form was characterised by much higher content of phosphate-rich polysaccharide (dispersed vs pelleted: 23 % and 1 % dw) and protein (55 % and 40 % dw, respectively). TEM-microscopy showed the thicker cell wall of the dispersed form, which did not manifest the third well-defined electron-dense smooth outer layer present in pellets. The cell wall of the pelleted form was less susceptible to mechanical and enzymatic destruction and demonstrated in AFM hardness tests 5-10 times greater nano-hardness than the dispersed form. Thus, the cell wall structure and properties are very different in the pelleted than the dispersed growth forms, where the narrower and chitin/glucans-richer cell wall of the pelleted form provides more effective protection from mechanical and enzymatic damages.