Fungal producers

A plausible sequence based on inspection of the structural formulae, and in which the roridin skeleton holds a central position, is shown in Scheme 6. The scheme assumes that the pathway in Baccharis, or its endophyte (see below), is essentially the same as in Myrothecium, and that all the fungal producers of macrocyclic trichothecenes use the same pathway. 

Of course, feeding deterrence may be cansed simply by the bitter, unpleasant taste of many alkaloids. However, all mechanisms of action discussed above may contribute more or less to the protection of their fungal producers as well as of the ergoline-positive convolvulaceous or graminaceous species against herbivores due to intoxications - lethal or survived (avoidance in future). Even pathogenic/para-sitic bacteria may be inhibited by certain clavines. 

Hood, R. D., and Szczech, G. M. 1983. Teratogenicity of Fungal Toxins and Fungal-Produced Antimicrobial Agents. In.- Plant and Fungal Toxins-Handbook of Natural Toxins, Vol.l, Keeler, R. R, and Tu, A. T., eds. New York, Marcel Dekker. pp.201-233. 

With the aid of cytosine permease, flucytosine reaches the fungal cell where it is converted by cytosine deaminase into 5-fluorouracil [51-21-8]. Cytosine deaminase is not present in the host, which explains the low toxicity of 5-FC. 5-Fluorouracil is then phosphorylated and incorporated into RNA and may also be converted into 5-fluorodeoxyuridine monophosphate, which is a potent and specific inhibitor of thymidylate synthetase. As a result, no more thymidine nucleotides are formed, which in turn leads to a disturbance of the DNA-synthesis. These effects produce an inhibition of the protein synthesis and cell repHcation (1,23,24). 5-Fluorouracil caimot be used as an antimycotic. It is poorly absorbed by the fungus to begin with and is also toxic for mammalian cells. 

Starch is converted enzymatically toglucose either by diastase present in sprouting grain or by fungal amylase. The resulting dextrose is fermented to ethanol with the aid of yeast, producing CO2 as a coproduct. Other by-products depend on the type of process. 

The pH has to be controlled - the acid which is produced has to be neutralised maintaining a pH in excess of 6.0. Below pH 3.0 the glucose oxidase is inactivated and in fungal systems low pH encourages citric add production. 

A possible example of this thesis is the crystalline insect toxin found in Bacillus thuringiensis spores and discussed here by Dr. Anderson. Although neither the bacillus nor its spores exhibit useful antibiotic activity against other microorganisms, the very specific toxicity to insects has become of major commercial interest. The enormous number and variety of fungal species available for further examination must lead inevitably to one or more which produces pesticidal metabolites. 

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