Toxins existence

This tremendous range of activity is brought about by the ability of B. thuringiensis and its varieties to produce not one, but at least five, substances toxic to insects. The possibility that a sixth toxin exists is matter for further investigation. 

Even within the lepidopteran pathotype, large differences in the insecticidal spectra of B.t. toxins exist. For example, screening of a large collection of B.t. strains has lead to the identification of strains highly toxic to Soodoptera littoralis, an insect which is insensitive to most commonly known B.t. strains. 

For many years, toxoids, which are immunologically active but non-toxic derivatives of toxins, have been used as in the prophylaxis and treatment of bacterial toxin-related diseases. These include notably diphtheria and botulism. Toxins must be produced as an essential precursor to the production of antitoxins and thus potential stocks of toxins exist from this route, which are produced in large-scale fermentation tanks. The existence of such stocks, which were outside the existing Chemical Weapons Convention, was the initial source of suspicion that toxins were being developed for use as toxic agents by the Soviet Union during the Cold War in the 1980s. 

In reality, the demands upon most freshwaters, whether from human potable supply, animal watering, aquaculture, recreation, or amenity are increasing, and a need exists to monitor the types, location and levels of cyanobacterial toxins. 

In view of the easy disruption of the nonaldehyde form of the toxin it seems probable that a loose complex in some form of acetal exists between the two hemiacetals (XIV, XV). When this is disrupted under mild conditions prehelminthosporol is formed and remains until converted under more vigorous conditions to helminthosporol, while prehelminthosporal (XIV, XIX) is too unstable and is converted to Helminthosporal. 

The PSP toxins represent a real challenge to the analytical chemist interested in developing a method for their detection. There are a great variety of closely related toxin structures (Figure 1) and the need exists to determine the level of each individually. They are totally non-volatile and lack any useful UV absorption. These characteristics coupled with the very low levels found in most samples (sub-ppm) eliminates most traditional chromatographic techniques such as GC and HPLC with UVA S detection. However, by the conversion of the toxins to fluorescent derivatives (J), the problem of detection of the toxins is solved. It has been found that the fluorescent technique is highly sensitive and specific for PSP toxins and many of the current analytical methods for the toxins utilize fluorescent detection. With the toxin detection problem solved, the development of a useful HPLC method was possible and somewhat straightforward. 

Targets for toxins can be considered to exist at various levels. Toxins may evolve which subdue prey by either blocking the systems responsible for locomotion, circulation, or for central coordination, in the potential victim. In order to disable these systems, advantage is often taken of the fact that their physiology depends upon specific transmembrane channels such as those for sodium, potassium, and calcium ions. 

Another possible target for toxins are the receptors for neurotransmitters since such receptors are vital, especially for locomotion. In vertebrates the most strategic receptor is that for acetylcholine, the nicotinic receptor. In view of the breadth of action of the various conotoxins it is perhaps not surprising that alpha-conotoxin binds selectively to the nicotinic receptor. It is entirely possible that similar blockers exist for the receptors which are vital to locomotion in lower species. As mentioned previously, lophotoxin effects vertebrate neuromuscular junctions. It appears to act on the end plate region of skeletal muscle (79,59), to block the nicotinic receptor at a site different from the binding sites for other blockers (81). 

Although significance of cholesterol hydroperoxides formation under physiological conditions is still unknown, they are apparently very important factors in the development of many pathophysiological disorders. Thus it has been shown [87] that 13ZE-Chl8 2-OOH exists in vivo in atherosclerotic lesions and is the primary toxin of oxidized human LDL. 

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