Microbial toxins in the soil

A toxin (Greek toxikon)
Poisonous substance produced by living cells or organisms
Small molecules, peptides, or proteins that capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules (enzymes or cellular receptors)
Severity: minor and acute to almost immediately deadly (as in botulinum toxin).
Microbial toxins are toxins produced by microorganisms,
including bacteria, viruses and fungi.
Abundant dispersal.

1. Microbial Toxins In The Soil Amjad Khan Afridi

2. Microbial Toxins A toxin (Greek toxikon ) P oisonous substance produced by living cells or organisms S mall molecules, peptides, or proteins that capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules (enzymes or cellular receptors ) S everity : minor and acute to almost immediately deadly (as in botulinum toxin). Microbial toxins are toxins produced by microorganisms, including bacteria, viruses and fungi. Abundant dispersal.

3. Different Types of Microbial Toxins Bacterial Toxins: Exotoxins : generated by the bacteria and actively secreted. Endotoxins : are part of the bacteria itself (bacterial outer membrane ) and it is not released until the bacteria is killed by the immune system . Clostridium tetani : Rod-shaped, anaerobic , gram-positive Found as spores in soil or in the gastrointestinal tract of animals. Biological toxin, tetanospasmin. The causative agent of tetanus (lockjaw) , a disease characterized by painful muscular spasms that can lead to respiratory failure .

4. Clostridium botulinum Gram-positive, rod-shaped Produces neurotoxins , known as botulinum neurotoxins types A-G, That cause the seen in botulism. Obligate anaerobic spore-former, endospores Commonly found in soil. Pseudomonas fluorescens Gram-negative, rod-shaped , an obligate aerobe H as multiple flagella F ound in the soil and in water. S trains (CHA0 or Pf-5, ) present biocontrol properties, protecting the roots of some plant species against parasitic fungi such as Fusarium or Pythium , as well as some phytophagous nematodes (Insects feeding on plants. P roduce the secondary metabolite 2,4-diacetylphloroglucinol (2,4-DAPG ) . natural phenol 

5. Mycotoxin: Fungi produces two categories of toxins. One of those produced by some mushrooms (such as Amanita phalloids, Cortinarius orellanus, Coprinus atrementarius, Inocybe sp ., etc) which are consumed directly as food. The poisoning caused by mushrooms is called “ mycetismus ”. Second type of toxins is those produced by certain molds, which grow on other food products. These are reffered as “mycotoxins”. Mycotoxins may be mutagenic or carcinogenic and may display specific organ toxicity.

6. Mycotoxins are produced by fungi as secondary metabolites at the end of the exponential growth phase. Mycotoxins are generally synthesized via polypeptide route. Induction of mycotoxicoses i.e. disease of animals and humans caused by the consumption of feed and food invaded by toxin producing fungi, thus pose serious threat to human and animal health. Most mycotoxicoses are caused by common and wide spread fungi as Aspergillus, Fusarium, Penicillum and Stachybotrys. Aspergillus and Penicillum produces toxins mostly in stored seeds, hay or commercially processed food and feeds. Fusarium produces toxins on corn and other stored grains and Stachbotrys on straw, hay and other cellulose products used as fodder or bedding for animals.

7. Aflatoxins are naturally occurring mycotoxins. Aflotoxins may be produced in infected cereal grains, most legumes, groundnut and other seeds. The moisture content in the seed or grains is the most important factor determining whether the aflotoxins producing fungus will grow or not. Moisture content >14% favours fungal growth. Aflotoxin , a polyketide toxin , is a metabolic product of Aspergillus flavus , Aspergillus parasiticus and other Aspergillus species. Aflotoxins consists of several chromatographically distinguishable components such as aflotoxin B 1 , B 2 , G 1 ,G 2 ,etc. The main target organ in mammals is the liver so aflatoxicosis is primarily a hepatic disease.

8. Fusarium toxins: Several species of Fusarium produce zearalenone (ZEA) and trichothecene (TC) toxins in molded corn. Z earalenone (F-2 mycotoxin) is produced by ; F . roseum , F . graminearum , F.oxisporum, F. moniliforme and F. tricinctum. It causes ‘ estrogenic syndrome ’ in swine . (Caused hypoestrogenism : Estrogen  deficiency )

9. Ergot alkaloids ( Ergotoxin ) : These are produced by Claviceps purpurea and other Claviceps species which grow in the heads of, produce sclerotinia and replace grains with the bodies containing ergot alkaloids . These fungi produce an extensive series of alkaloids . The alkaloids are structurally related to lysergic acid diethylamide (LSD ), a well known psycho-active drug / hallucinogenic  drugs. Ergots cause abortion and smooth muscle contraction which sometimes may lead to the loss of limbs. white mold

10. Patulin: It i s polyk e tide c arcin o genic to x in produced by Pen i ci l l i um urticae, P . patulum , P . griseofulvum , P . claviforme, etc,. It is toxic to bacteria and some fungi, higher plants and animals. Stachybotrys toxins: These toxins are produced thye species of stachybotrys ( black mold) on straw, hay, other fodders and animal feeds, etc. S tachybotrys toxins cause diseases like haemorrhage, necrosis and general cell damage in domesticated animals.

11. Alternaria toxins: Several species of Alternaria produce toxins that have been found in apple, tomato , blue berry, etc. T he toxins produced include alternariol, monomethl ether, alternune, tenuazoic acid and altertoxin. Aspergillus and Penicillium produce many other kinds of toxins such as yellow rice toxins and tremorgenic toxins. Ochratoxins produced by A . ochraceus causes fatty liver disease.

12. Effects of Mycotoxins ( aflatoxin B 1 ) Mycotoxins (100 or 200 μg kg −1 soil) significantly decreased nodule number, nodule fresh weight and total nitrogenase activity, leading to reductions in dry matter accumulation and nitrogen yield of the bean suppressed specific nitrogenase activity. NADH-dependent glutamate dehydrogenase (NADH-GDH) as well as glutamate synthase (NADH-GOGAT) activities. I nhibited synthesis of leghaemoglobin / legoglobin (oxygen carrying)   , carbohydrate and protein in the nodule cytosol ( cytoplasmic matrix) . I nterference with normal nodule physiology and function.

13. Bacillus thuringiensis (Bt) Gram-positive, soil-dwelling bacterium N aturally in the gut of caterpillars ( moths, butterflies, ) A erobes capable of producing endospores. During sporula t ion prod u ce cr y s tal pro t e ins ( proteina c e o us inclusions), δ-endotoxins ( crystal proteins or Cry proteins), E ncoded by cry genes ( located on the plasmid)

14. S pec if i c activ i t i e s aga i nst ins e ct spec i es of orde rs Lepidoptera (moths and butterflies), Diptera (flies and mosquitoes), Coleoptera (beetles ), hy m enopt e ra (wasps, bees, ants and nematodes , sawflies). Use as inse c ti c ide s , gen e tic a lly m odified crops us ing Bt genes. Biological alternative to a pesticides. M any cr y sta l - p roduci n g B t s t r a i n s that do not have insecticidal properties. Used as specific insecticides under trade names such as Dipel and Thuricide

15. Bt crops Bt crops Cry Protein Target pests Maize Cry1Ab European corn borer ( Ostrinia nubilalis),Corn stalk borer ( Sesamia nonagrioides),corn earworm ( Helicoverpa zea Boddie) Cotton Cry1Ac Bollworm ( Earias spp ,Helicoverpa spp, Heliothis spp, Pectinophora spp)

16. Mechanism of Toxicity Inges t io n : ICP (In s e ct i ci da l c r y sta l l ine p r o teins) spore complexes of Bt by susceptible insect larvae Activation: alkaline pH, in midgut ICP is dissociated to protoxin form protoxin is then activated to holotoxin by gut proteases . Paralysis: gut becomes paralysed larva ceases to feed

17. Binding: Binding of the ICP to receptors major determinant of ICP specificity Pore formation: midgut epithelial cells damaged, the haemolymph and gut contents can mix. re su l ts i n favourable condi t ions for the B t spor es to germinate. vegetative cells of Bt and the pre-existing microorganisms in the gut proliferate in the haemocoel causing septicaemia, Mortality of larvae

18. Mechanism of Toxicity

19. Thank You 7 th April, 2021, Wednesday