Drosophila lifespan enhancement by exogenous bacteria

Abstract

We researched the lifespan of Drosophila under axenic conditions compared with customary procedure. The experiments revealed that the presence of bacteria during the first week of adult life can enhance lifespan, despite unchanged food intake. Later in life, the presence of bacteria can reduce lifespan. Certain long-lived mutants react in different ways, indicating an interplay between bacteria and longevity-enhancing genes.

Fig. 1.

Survival curves of axenic flies compared with those of flies maintained under customary, nonaxenic conditions. (A) In the presence of bacteria, mean lifespan was 30% longer (P < 0.0001). (B) Starting with axenic embryos, bacteria were introduced during development by adding a homogenate of nonaxenic flies. Introduction of bacteria at that time produced a 30% increase in longevity (P = 0.002). (C) Starting with axenic embryos, bacteria were introduced either during development or after day 7 of adult life. The latter flies' lives were 25% shorter than those of flies receiving bacteria during development (P < 0.0001). (D) Starting with axenic embryos, bacteria were introduced either during development or after day 2 of adult life. Introduction of bacteria at adult day 2 promoted longevity as well as if introduced during development (P = 0.23). (A and B, 22°C; C and D, 25°C). Error bars represent SEM.

Fig. 2.

Critical period for extension of longevity by the presence of bacteria by using antibiotics. (A) Lifelong (from embryo onward) antibiotic in the food results in a 35% reduction in longevity (P < 0.0001), consistent with that observed under axenic conditions. (B) Flies developed on normal food. Flies were raised on nonsterile food until adult emergence; they were then transferred, at various times, to antibiotic food. Those transferred to antibiotic food at days 1 and 2 showed a reduction in longevity, compared with flies maintained lifelong on nonsterile food. However, flies not transferred to antibiotic food until days 4 or 7 showed similar lifespans to untreated flies. (C) Flies developed on antibiotic food. Flies were raised on antibiotics from the embryo up to adult emergence and then transferred, at various times, to nonsterile food. Flies transferred at days 1 or 2 showed no difference compared with flies under ordinary conditions. However, flies transferred after days 4 or 7 showed a reduction in longevity comparable to flies maintained lifelong on antibiotics. The bars in B and C correspond to two experiments, each of at least 90 flies (the day 7 experiment was a single trial). Error bars represent SEM.

Fig. 3.

Presence of bacteria late in life is deleterious. Flies were raised and maintained under ordinary (nonsterile) conditions to age 31 days and then either transferred to antibiotic food or maintained on standard food. This late addition of antibiotics resulted in an 8% increase in mean lifespan (P < 0.0001). These results confirm at 25°C the results shown in Table 1, which were from experiments done at 29°C. Error bars represent SEM.

Fig. 4.

Feeding rate is unchanged by the antibiotics used. Food intake was determined by using ³²P-labeled food under four different conditions. Flies were raised from embryos to adulthood on either antibiotic-containing or standard food, and then, at adult age (7 days), they were transferred either to antibiotic or standard food and allowed to feed for 18 h. Food intake, as determined by scintillation counting, showed no significant differences under the four regimes. Bars represent the results of two trials with 20 flies each. Error bars represent experimental range.

Fig. 5.

Host genotype can enhance or suppress the effect of bacteria on lifespan. (A) w¹¹¹⁸ flies. For w¹¹¹⁸ flies, the presence of antibiotic throughout lifespan decreases longevity (P < 0.001). (B) EcR^v559fs flies. Similar treatment does not affect the long-lived heterozygous EcR^v559fs strain (P = 0.2). (C and D) No antibiotics versus with antibiotics. The enhancer trap strain DJ817 is 30% longer lived than w¹¹¹⁸ in the presence of bacteria (P < 0.001) (C), but removal of bacteria with antibiotics (D) eliminates the difference in their lifespans (P = 0.3).