A statistical approach to medium optimization for growth and toxin production by the bacterium Bacillus thuringiensis : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Biotechnology at Massey University, Palmerston North, New Zealand

Abstract

Bacillus thuringiensis is a Gram positive spore-forming bacterium. Knowledge of its pathogenicity against the larval stages of certain lepidopterous insects has been known for over 70 years. Ishiwata (1902) was the first to isolate it from dying silkworm larvae. Later Berliner (1915) isolated it from sick larvae of Anagasta kuhniella. He noted the existence of a parasporal body or "Rostkorper" in sporulated cells. These observations were confirmed by Mattes (1927), but it was not until 1953 that Hannay (1953) characterized the parasporal body as a crystal. The crystal has since been known to play a key role in the pathogenicity towards the most susceptible lepidopterous larvae. In recent years a considerable degree of interest has been aroused on the use of biological methods for insect control as against the use of chemical insecticides. Among many biological products considered as insect control agents, the crystal produced in the bacterium B. thuringiensis is one of the most hopeful. Industrial organisations in several countries are presently engaged in fundamental research and commercial scale production of insecticidal preparations based on this bacterium (Falcon, 1971; Pendleton, 1969). Apart from the crystal, which might be considered as an enterotoxin, a number of exotoxins are also known or postulated to be produced by B. thuringiensis. Heimpel (1967a) suggested the following nomenclature: δ -endotoxin, or the proteinaceous crystal; α-exotoxin, a lecithinase C or phospholipase C; β -exotoxin, a thermostable exotoxin or "fly factor"; γ -exotoxin (an enzyme that clears egg yolk agar, not yet identified). The toxicity for insects of the β -exotoxin and the δ -endotoxin has been substantiated, but the efficiency of the so-called γ -exotoxin has not been proved. Quite recently Krieg (1971) suggested that the α -exotoxin is not identical with lecithinase C. He concluded that the α -exotoxin is a thermosensitive exotoxin of proteinaceous character which is produced during growth phase by strains of B. thuringiensis and of B. cereus. Krieg (1970) also isolated a relative heat stable bacteriocin produced by B. thuringiensis which he called Thuricin. He suggested that this is a polypeptide and can cause inhibition of growth of Gram positive bacteria and antagonism between several strains of B. thuringiensis.[FROM INTRO]