pH-controlled continuous cultivation of mycoplasmas.

The continuous cultivation of mycoplasmas in a pH-controlled metabolistat was investigated with the fermentative strain Mycoplasma mobile 163K and the nonfermentative strain Mycoplasma arthritidis ISR1. The addition of medium and the removal of culture suspension were regulated by acid production from glucose by M. mobile 163K and by ammonium production from arginine by M. arthritidis ISR1, respectively. For both strains the optimal pH for continuous growth was 7.0. The steady state could be maintained for at least 21 days. With CFU of 8.4 X 10(9) ml-1 (M. mobile 163K) and 3.2 X 10(9) ml-1 (M. arthritidis ISR1), the cell concentrations were slightly higher than those obtained in batch cultures. The dependence on the adjusted pH values was measured for several parameters, such as flow rate, CFU, glucose fermentation or production of ammonia, and gliding velocity. Since the long lag phases of batch cultures can be avoided, pH-controlled continuous cultures provide an appropriate system for the production of mycoplasma cells.     

Effects of exposure to short-term heat stress on fitness components in Drosophila melanogaster

Effects of thermal stress on survival and reproductive success in ten recently collected isofemale lines of Drosophila melanogaster were compared for flies treated as follows: always held at 25° C, placed in an incubator set at 37° C for 120 min, or exposed to 40° C in an incubator for 90 min, with or without previous exposure to 37° C. Short-term exposure to the higher temperature greatly reduced adult survival, the mating frequency of males and females, and female fecundity, which was measured as offspring produced over ten days. Male fertility, measured as the progeny produced by a female mated once, differed little among treatments. Previous exposure to a high, but non-lethal, temperature before exposure to the higher one, improved survival of males and females, and improved offspring production of females. Genetic variation was present among lines for offspring production, but genetic variation for survival was not significant, and genotype by environment interactions for fitness components of females were small. These results indicated low genetic variation in thermal resistance in the studied population, such that a threshold for temperature stress probably exists, above which local extinction is more likely than the evolution of resistance.