High temperature of development and selection of Bacillus thuringiensis-supernatant-resistant females in a Drosophila melanogaster Oregon R strain

Abstract

The supernatant of Bacillus thuringiensis cultures contains a thermostable toxin: the beta exotoxin or thuringiensin, which in vivo acts as a preferential inhibitor of ribosomal RNA synthesis. Added to Drosophila melanogaster culture medium, it induces, during the flies' development, a lethal effect that is, in our Oregon R strain, greater for females than for males. The authors have previously shown that a diminution of the ribosomal DNA amount increases the sensitivity to the lethal effect of the supernatant. From a stock subjected for several generations to a 28 degrees C temperature and more, they have spontaneously obtained a variant population where males and females have similar resistance. It is shown here that this difference between the two populations is expressed in the X/X female genotypes, and that there is a correlation between the sensitivity to the lethal effect of the Berliner Bacillus thuringiensis supernatant and the sensitivity to the effect of the 28 degrees C developmental temperature; genotypes resistant to the lethal effect of the temperature were positively selected when the temperature of development was increased. The better resistance of these genotypes could be related to more active ribosomal units on the X chromosome.

Increase in the resistance to the Bacillus thuringiensis supernatant effect in a Drosophila melanogaster wild type Oregon R line

“…The initial and variant Oregon R populations do not exhibit any difference on a standard medium at 25°C. However, these two populations express differences when they are bred at 28°C: this temperature has a lethal effect during development and females of the variant population are more resistant than those of the initial population; we have shown that genotypes resistant to increased temperature were present in the initial stock and have been positively selected when bred at the high temperature (Paumard-Rigal & Rosenberg-Bourgin, 1990). We have postulated that variation in the degree of resistance to Bacillus thuringiensis supernatant could reveal variations in the amount of active rDNA units.…”

“…We had previously observed a correlation between the sensitivity of different genotypes to the lethal effect of the increase in temperature and to that of the Bacillus thuringiensis supernatant (Paumard-Rigal & Rosenberg-Bourgin, 1990). The 3B line females have more active ribosomal transcriptional units compared to the 1C line females.…”

“…Heterogeneity of our initial Oregon R population had been observed in 0. MELANOGAS TEA RESISTANCE TO B. THURINGIENSIS 545 temperature-resistant tests on individual X/O genotypes (Paumard-Rigal & Rosenberg-Bourgin, 1990). …”

“…We have postulated that variation in the degree of resistance to Bacillus thuringiensis supernatant could reveal variations in the amount of active rDNA units. By successive individual crosses, two lines, whose females differ extensively for resistance to beta-exotoxin, have been isolated: the 3B line from the variant population and the 1C line from the initial one (Paumard-Rigal & Rosenberg-Bourgin, 1990). We report here on the results of genetical and molecular studies of these two Oregon R lines.…”