Aflatoxin B1 induction of lysogenic bacteria

Prophage induction and filamentation in Bacillus thuringiensis caused by the genotoxic mycotoxin aflatoxin B1

Cultures of the lysogenic strain of Bacillus thuringiensis var. tolworthi were made in the presence of various drugs. The determination of bacterial size and plaque forming units (by using an indicator strain of B. thuringiensis var. galleriae) as well as colony forming units were then performed. Treatment of lysogenic cells by aflatoxin B1: provokes the formation of elongated cells (filamentation); induces a pathway that leads to the induction of prophage. Results of the present study indicated that filament formation and bacteriophage induction are two commonplace effects that occur in virtually every member of this cellular population exposed to low doses of certain drugs such as aflatoxin B1 (10 micrograms/ml); all of which have in common the ability to produce damaging changes in DNA. The following findings support the hypothesis that error-prone repair mechanisms seem to be present in B. thuringiensis as in Escherichia coli.

Conditions for induction of bacteriophage from lysogenic Bacillus megaterium with aflatoxin B1

The present study was conducted to determine whether or not aflatoxin B1 was an effective inducing agent for lysogenic bacteria and to characterize some of the parameters involved in induction. A lysogenic strain of Bacillus megaterium (NRRL-B-3695) and an indicator strain of this species (NRRL-B-3694) were used. Cultures of the lysogenic strain were incubated for various periods of time in the presence of aflatoxin B1. Plaque-forming units as well as colony-forming units were then determined. Results of the present study indicated that bacteriophage lysogenizing B. megaterium could be induced with aflatoxin B1. The optimum concentration for induction was 25 micrograms of toxin per ml of early-log-phase culture. Evidence suggested that: (i) higher concentrations of aflatoxin B1 formed hydrophobic complexes which would not efficiently induce B. megaterium; (ii) the toxic effect of aflatoxin B1 severely limited the number of cells which could be induced prior to killing action of the toxin; and (iii) concentrations less than 25 micrograms of aflatoxin B1 per ml were not efficient inducers of bacteriophage production nor did they demonstrate the toxic effect observed at higher concentrations.