Microbes as Bio-control Agents and Biofertilisers

Widespread use of chemical pesticides and insecticides harms human health and pollutes the environment, so biocontrol — using microbes, or naturally occurring substances derived from plants and animals, to manage a specific pest — offers a safer alternative; using a microbe or other biological agent for pest control specifically is called a biopesticide, and simple examples from the wider ecosystem include ladybird beetles controlling aphids and dragonflies controlling mosquito larvae. The soil bacterium Bacillus thuringiensis (Bt) is the most widely used microbial biopesticide (Fig. 9.5): during sporulation it produces crystalline Cry (delta-endotoxin) proteins encoded by cry genes, which have specific activity against insects of the orders Lepidoptera, Diptera, Coleoptera and Hymenoptera. When a susceptible insect ingests the crystals, its alkaline gut dissolves them into an active soluble toxin that inserts itself into gut-cell membranes and paralyses the digestive tract, so the insect stops feeding and starves to death; scientists have transferred cry genes into crop plants to create genetically engineered insect-resistant varieties such as Bt-cotton. Bioweedicides similarly use compounds and secondary metabolites derived from microbes such as fungi, bacteria or protozoa to destroy weeds without harming useful plants — the first bioherbicide (a mycoherbicide), developed in 1981 from the fungus Phytophthora palmivora, controls the growth of strangler vine in citrus crops. Trichoderma specie …