Figure 1. L. plantarum (Lp) rescues the developmental delay due to amino acid (AA) imbalance.

(A,B) Developmental timing of germ-free (GF) larvae (grey) and Lp-associated larvae (green) on FLY AA diets with a –70% (A) or –60% (B) decrease in each essential AA (EAA). Boxplots show maximum, minimum, and median D50 (median time of pupariation) of five replicates. Each replicate consists in one tube containing 40 larvae. L2: larvae stalled at the L2 stage. L3: larvae stalled at the L3 stage. For each diet in (B), we used a Cox proportional hazards model to test the effect of the diet, association with Lp, and the interaction between these two parameters. We show the p-values of the interactions between diet and association with Lp after correction by the FDR method. n.s.: non-significant, **: p-value <0.01, ***: p-value <0.001. (C) Developmental timing of larvae raised on balanced diet (FLY AA, filled circles) or imbalanced diet (FLY AA –60% Val, empty circles). The graph represents the total fraction of emerged pupae over time as a percentage of the final number of pupae. The graph shows five replicates per condition (mean and standard deviation). Each replicate consists in one tube containing 40 larvae. We used a Cox proportional hazards model to test the effect of the diet, the association with Lp, and the interaction between these two parameters. (D) Developmental timing of larvae raised on balanced diet (FLY AA, filled circles), on imbalanced diet (FLY AA Val –60%, empty circles), on imbalanced diet adjusted with His (FLY AA Val –60%+His, triangles) or on imbalanced diet adjusted with Leu (FLY AA Val –60%+Leu, squares). The graph represents the total fraction of emerged pupae over time as a percentage of the final number of pupae. The graph shows five replicates per condition (mean and standard deviation). Each replicate consists in one tube containing 40 larvae. (E) Valine concentration in the haemolymph of larvae. The graph shows the mean and standard deviation of three replicates. Each replicate consists in the haemolymph of 10 larvae pooled together. We used an ANOVA followed by post hoc Dunnett’s test to compare the mean of each condition to the mean of the condition GF on imbalanced diet. **: p-value <0.01.

Figure 1—figure supplement 1. Characterization of the growth promoting effect of L. plantarum on AA-imbalanced diet.

(A–D) Developmental timing and survival rate: the graphs show five replicates (mean and standard deviation). Each replicate consists in one tube containing 40 larvae. (A) Developmental timing of larvae raised on balanced diet (FLY AA, filled circles) or on severely imbalanced diets (FLY AA –80% Val, empty circles, FLY AA –90% Val, empty triangles) in germ-free (GF) condition (grey) or L. plantarum (Lp)-associated conditions (green). The graph represents the total fraction of emerged pupae over time as a percentage of the final number of pupae. GF larvae reared on severely imbalanced diets (–80% or –90% Val) did not reach pupariation. (B) Developmental timing of larvae raised on balanced diet (FLY AA, filled circles) or on imbalanced diet due to excess Val (FLY AA +60% Val, empty circles) in GF condition (grey) or Lp-associated conditions (green). (C) Egg-to-pupa survival of GF larvae (in grey) and Lp-associated larvae (green) on balanced diet and imbalanced diets. Survival was calculated as the final number of pupae divided by the initial number of eggs (i.e. 40 per replicate). We performed a Kruskal-Wallis test followed by post hoc Dunn’s tests to compare each condition to the condition GF on balanced diet and found no statistically significant difference. (D) Developmental timing of larvae raised on imbalanced diet (FLY AA Val –60%) in GF conditions (grey), in live Lp-associated conditions (filled green circles) or after supplementation with the same quantity of heat-killed (HK) Lp (empty green circles). We used a Cox proportional hazards model to compare the effect of Lp and HK Lp to the GF condition. (E–F) Food intake of GF larvae (grey) or Lp-associated larvae (green) reared on balanced diet (E) or imbalanced diet (F). Larvae were transferred on coloured food, and food intake was calculated as the optical density (OD) of the food ingested by the larvae over time. The graph shows the mean absorbance and standard deviation of five replicates per condition. Each replicate consists in 5 larvae.