The Reaction Dimension for Fungal Enzyme Catalysis of an Organic Dye
CAMERON L. JONES*, DAVID E. MAINWARINGþ, AND GREG T. LONERGAN*
*Centre for Applied Colloid and BioColloid Science, School of Chemical Sciences, Swinburne University of Technology, Victoria 3122, Australia
þDepartment of Applied Chemistry, Royal Melbourne Institute of Technology, Melbourne 3001, Australia
We investigate the kinetics for an enzyme induced decolorization of an organic dye in solid surface fermentation (SSF). In the SSF system described here, colonies of the white-rot fungus Pycnoporus cinnabarinus were germinated on agar media containing basal levels of ground wood powder (0.2% w/v). Treatment media contained a concentration gradient of the aminoanthraquinone dye, Remazol Brilliant Blue R (RBBR) at 100, 200, 300, 400, 500, 1000ppm in small volume (25mL) standard petri- plates. Colour image processing and analysis was used1 to record daily zones of decolorization over a 7 day growth cycle. Dye decolorization progressed as radial bands originating from the inoculation site over time. The tangential radial size of the concentric bands was a function of (1) endogenous fungal growth rate, (2) substrate dye concentration, (3) enzyme induction - in addition to constitutive activity. SSF occurred in a gel (2% w/v agar) which is a cross-linked polymer forming a large cluster at the critical point of gelation. The network of nearest neighbour connected paths confers percolation properties for enzyme diffusion through the gel. We hypothesised that the conformational geometry, i.e. the spatial distribution of RBBR dye molecular clusters would influence the kinetics of dye decolorization by fungal exo-enzymes (i.e. laccase for P. cinnabarinus).
This paper provides evidence for a mathematical power law termed Fractal Catalysis which goes some way towards describing the decolorization rates in terms of reaction-diffusion kinetics. We conclude that at low dye concentrations, a lack of geometric screening allows for a greater exposed particle size (R) available for reaction compared with higher dye concentrations where the effect of geometric clustering/screening limits the diffusional accessibility of the enzyme. This restricts initial catalytic activity to the cluster boundaries in non-stirred SSF systems. The scaling law between catalytic activity, a (mol.time-1.particle-1) and particle size, 2R (measured by twice the radius R) follows: a~RDR with DR equal to the reaction dimension2. The graph shows the straight line power law behaviour, and the measured reaction dimensions are discussed with reference to scale-up implications for SSF.
1. Jones, C.L., Lonergan, G.T. and Mainwaring, D.E. (1993). Biotech Tech. 7: 645-650
2. Farin, D. and Avnir, D. (1988). J.Am.Chem.Soc. 110: 2039-2045.
This paper should be referenced as follows:
TITLE: "The Reaction Dimension for Fungal Enzyme Catalysis of an Organic Dye"AUTHOR: Cameron L. Jones, David E. Mainwaring and Greg T. Lonergan
AFFILIATION: Centre for Applied Colloid and BioColloid Science, Swinburne University of Technology, School of Chemical Sciences, GPO Box 218, Hawthorn, Victoria, 3122, Australia and Department of Applied Chemistry, Royal Melbourne Institute of Technology, Melbourne, Victoria, 3001 Australia
EMAIL: CJONES@swin.edu.au
DATE: Accepted for Publication: 12/07/96
URL REFERENCE: http://www.swin.edu.au/chem/bio/aba96/environ1.htm
SOURCE: 10th International Biotechnology Symposium and 9th International Symposium on Yeasts; Sydney Convention Centre, Sydney, Australia, 25-30 August 1996
PRESENTATION DATE: Thursday 29 August 1996 - Poster Session 8 - Environmental Biotechnology