Mycelial systems

I now turn to an example concerning antibiotic production, where the problem is increasing productivity in oxygen-limited, very viscous, mycelial systems. In many of these antibiotic-producing biosystems, a 5% improvement in yield represents several million dollars of increased profit per year—obviously, there is great motivation to try to get even that 5% improvement. 

One would think a solution to increase the productivity would be to use oxygen enrichment, not just during the choke-out period but also during the remainder of the fermentation in order to sustain the productivity. This does not work because of broth viscosity and gas holdup problems. In highly mycelial systems, a 15% increase in cell mass doubles the viscosity. The volumetric oxygen mass transfer coefficient and the bubble rise velocity—... 

Donnelly, D. D., Boddy, L. Leake, J. R. (2004). Development, persistence and regeneration of foraging ectomycorrhizal mycelial systems in soil microcosms. Mycorrhiza,... 

SoderstrSm, B. Read, D. J. (1987). Respiratory activity of intact and excised ectomycorrhizal mycelial systems growing in unsterilised soil. Soil Biology and Biochemistry,... 

Donnelly, D.P., and L. Boddy. 1997. Development of mycelial systems of Stropharia caerulea and Phane-rochaete velutina on soil Effect of temperature and water potential. Mycol. Res. 101 705-713. 

The AM fungus develops two associated mycelial systems, one within the root, from which the other extends into the soil. This stmctural continuum at the interface between plant root and soil make these symbionts particularly relevant in plant-to-soil interactions. The extraradical mycelium develops links between roots... 

Donnelly, D.R, Wilkins, M.R and Boddy, L. (1995). An integrated image analysis approach for determining biomass, radial extent and box-count fractal dimension of macroscopic mycelial systems. Binary, 7,19. 

DonneUy, D P, Boddy, L. and Wilkins, M.R (1999). Image analysis - a valuable tool for recording and analysing development of mycelial systems. Mycologist, 13, 120. 

Figure 8.1 Image preprocessing of mycelial systems in soil microcosms (a) unprocessed image (b) masking of central inoculum and uncolonised soil area (c) thresholded binary image (d) overlaid grid for box-count determination of fractal dimension (e) close-up of mycelial colonisation of wood resources and localised mycelial patch production (encircled dotted lines).

Figure 8.4 Digital images of ectomycorrhizal mycelial systems of (a) Suillus bovinus and (b) Paxillus involutus in peat microcosms (in association with Pinus sylvestris) (c) the pine root pathogen Rhizina undulata extending from a 50 cm section of pine stem (d) Armillaria ostoyae extending from a 8cm pine wood resource across nonsterile soil compacted in 24 cm X 24 cm trays.

Figure 8.5 Digital images of mycelial systems of (a) Agrocybe gibberosa, (b) Phallus impudicus, (c) Stropharia caerulea, (d) Stropharia aeruginosa after 28 days, (e) Coprinus picaceus after 180 days (image courtesy of Alaa Alawi) and (f) Resinicium bicolour after 30 days (image courtesy of GM. Tordoff), extending from 4 cm beech wood resonrces onto non-sterile soil which has been compacted in 24 cm x 24 cm trays. White circles (a-d) are inert plastic caps I are inocula. Note the differences between the mass (Dbm) and snrface (Dbs) fractal dimensions of the species.

Figure 8.6 Digital images showing development of a mycelial system of Hypholoma fasciculare after (a) 14 days, (b) 21 days and (c) 35 days, extending from 4cm beech wood resource onto nonsterile soil compacted into 24 cm x 24 cm trays.

Figure 8.8 Change with time of surface (a, b) and mass (c, d) fractal dimensions of mycelial systems of (a, c) Hypholoma fasciculare and (b, d) Phanerochaete velutina extending from a 4 cm beech wood resources across nonsterile soil, compacted in 24 cm x 24 cm trays, either to inert control baits (squares) or 4 cm uncolonised wood resources (circles) (modified from [61]).

Water potential" (which determines ease or difficulty of obtaining water), temperature and pH all affect fractal structure of mycelial systems. Moreover, they exert interactive effects with each other and with other abiotic variables, e.g. sand content of soil [66, 68], Temperature effects on fractal dimensions of Stropharia caerulea were variable (Table 8.3) [69]. At 5°C, it took 9 days longer to achieve the Dgs values obtained at 10-20 °C, and 12 days longer to achieve the Dbm values for Stropharia caerulea. At 25 °C, both fractal dimensions of Stropharia caerulea were significantly lower than values of mycelial systems at 10-20 °C, until 26-29 days. There were also slight intraspecific differences between strains of Stropharia caerulea [69]. For Phanerochaete velutina, both fractal dimensions at 5 °C were significantly less than at 10-25 °C for the first 20 days and 14 days respectively. It is unclear what is mediating these temperature effects. 

Table 8.3 Effect of temperature on the fractal geometry of mycelial systems of Stropharia caerulea and Phanerochaete velutina, extending from beech (Fagus sylvatica) wood block inocula across soil after 30 days. Data from [69].

Table 8.4 Changes in fractal geometry of mycelial systems during interactions between Stmpharia caerulea and other cord-forming, saprotrophic basidiomycetes in trays of compressed soil. Data from [61].

Donnelly, D.P. and Boddy, L. (1998). Developmental and morphological responses of mycelial systems of Stropharia caerulea and Phanerochaete velutina to soil nnirient enrichment. New PhytoL, 138, 519-531. 

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