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Diagram of a Spore of Aspergillus Germinating on a Starch Substrate

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 Spores germinate if there is moisture, nutrient, and a suitable temperature for the species.  As it grows, the germ tube releases exogenous enzymes into the substrate (e.g. amylases, blue arrow). These break down the starch to their component glucose molecules that are waater soluble and absorbed by the fungus (curved black arrows). Free living bacteria (dark blue rods) in the vicinity, however, can take advantage of the 'free' glucose and multiply. To protect the substrate for its own use, the fungus can release a 'chaser' of antibiotics (e.g. patulin, aflatoxin: red arrows) to inhibit or eliminate competition from bacteria and other microorganisms. You can appreciate the limitation of exogenous secretion of enzymes and how fungi can compensate for this limitation.  

Alternatively fast growing fungi such as Rhizopus and other Mucorales (the so-called 'sugar fungi') are rapidly growing opportunists.   They use up the simple sugars avaialble very rapidly and grow away from the source before the bacteria have built up to competitive levels.   Mucorales do not produce antibacterial antibiotics.   

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