Using a scanning electron microscope to examine the insects outer surfaces, the researchers showed that some of the bacteria were even banding together, forming continuous biofilms. Yet treatments that reduced the number of bacteria had no effect on life span, they found. That discovery led the researchers to conclude that, at least under optimal laboratory conditions, Drosophila can tolerate a significant number of bacteria and mount a strong innate immune response against them without cutting their 65-day lives any shorter.
There has been some thinking in general that life span is regulated according to trade-offsthat the body has only so much energy to devote to different processes, Tower said. If you devote a lot [of energy] to controlling bacteria, preventing them from growing to a toxic level, then that energy isnt available to maintain tissues and organs. However, we found no effect on the animals longevity even when their bacteria are taken from one extreme to the other.
Nevertheless, he added, the bacterial infestations seen in the aged flies have to be a quality of life issue.