Fungal Cell Factories - Food and Industrial Bioproducts and Bioprocessing - page 200

8 Fungal Cell Factories
Sue A. Karagiosis and Scott E. Baker
8.1 FUNGI AND FUNGAL BIOTECHNOLOGY
Human history and fungi have been profoundly intertwined for centuries. This large and
diverse group of eukaryotic, heterotrophic microbes derives its energy through extracellular
digestion of organic matter. Some of these microbes exist as the bane of mankind, notably
pathogens of crops, plants or people. Alternatively, a multitude of beneficial and valuable
resources have been obtained by harnessing the metabolic activities of fungi. Fungi are a
major food source and essential for the creation of bread, veined cheeses, alcoholic
beverages, and traditionally fermented foods such as tempeh, miso and soy sauce to just
name a few. Commercial manufacture of antibiotics, many organic acids and enzymes are
driven by fungal biotechnology. Additionally, these organisms are a treasure trove of yet
undiscovered bioactive secondary metabolites with possible drug discovery and
pharmaceutical applications.
Applications of fungal biotechnology allow for the industrial exploitation of a fungal
culture's innate biochemical activities. Molds secrete an impressive diversity of enzymes
and metabolites, some of which are important commodities for the food, agricultural,
enzyme and pharmaceutical industries. Fungi are commercially cultured by various means
to obtain high process productivity and product yields. Highlighted here are a few of the key
processes, as these techniques have been reviewed extensively elsewhere (Murphy and
Horgan, 2005 ; Ruijter et al ., 2002 ; Sahasrabudhe and Sankpal, 2001 ; Bentley and Bennett,
2008 ; Fazenda et al ., 2008 ).
One of the oldest methods, solid-state fermentation or the koji process , uses solid
substrates, such as steam sterilized fibers or wheat bran, to cultivate the mold inoculum.
This technique has been central to traditional food and beverage fermentations throughout
Asia for thousands of years. Today solid-state fermentation is the cultivation method of
choice for the commercial production of many enzymes and is gaining popularity in areas
including bioremediation, detoxification of agro-industrial waste and biotransformation of
crop residues for nutritional enrichment (Pandey et al ., 2000 ; Singhania et al ., 2009 ).
Surface fermentation , used in the early production of both penicillin and citric acid, is
carried out in shallow, nutrient medium-filled stainless steel trays instead of on a solid
matrix. These trays are stacked within an aseptic fermentation chamber, and the fungal
mycelium develops as a mat on the surface of the liquid.