Article Figures & Data
Figures
- FIG 1
Description of lrp mutations. The lrp gene is made of two domains, HTH and RAM. The study used four lrp mutants, each with a single point mutation that strains 23, 42, 44, and 51 do not carry. Strains 36 and 39 carry different nonsense mutations in codon position 53, leading to a frameshift (FS). Strains 25 and 29 carry each a missense mutation in codon position 120, leading to different amino acids. Strain 40 carries a nonsense mutation (duplication) in codon position 124, leading to a Stop codon (*).
- FIG 2
Survival of adult Drosophila melanogaster flies upon infection with wild-type or lrp mutant Xenorhabdus nematophila. (A) Survival over time of hosts when injected with 1,000 bacteria. Wild-type bacteria, represented individually by blue dotted lines, always killed their hosts faster than lrp mutants, represented individually by red dotted lines. Solid lines represent the pooled wild-type (blue) and mutant (red) strains. Black dashed lines show the median lethal time in hours (LT50) of wild-type strains. The numbers of host individuals are mentioned in parentheses. (B) Virulence of each bacterial strain. Each dot represents the death hazard ratio relative to sham infection calculated from the Cox model used to analyze the survival in panel A. Blue represents infection with wild-type bacterial strains, and red represents infection with mutant strains. Details of strain numbers for reference are given in Fig. 1.
- FIG 3
Bacterial success during the first step of the infection. (A) Bacterial load estimated at 8 h postinjection in immunodeficient (IMD) flies (genotype Dredd55) and in the control genetic background (w1118). The lowercase letters represent the significant differences between loads of different bacterial strains in hosts with a functional immune system. Wild-type bacterial strains reached a higher density than strains with a mutation in lrp. Only mutant strain 29 is intermediate. “p” indicates the P value of the difference in bacterial load between immunodeficient hosts and healthy hosts. Unlike other strains, those with a nonsense lrp mutation proliferated better in the immunodeficient host. Experiments were replicated with three (strains 23 and 29) or five (all other strains) different overnight bacterial cultures and fly batches. (B) Bacterial load at injection and 8 h postinjection in immunodeficient and healthy hosts. “p” indicates the P value of the interaction between time and genotype testing for the difference in proliferation. This approach validates that strain 40, with a nonsense lrp mutation, proliferates less in the presence of the immune system. Experiments were replicated with three different overnight bacterial cultures and fly batches. (C) Correlation between early growth in wild-type hosts of the bacterial strains with or without mutation and the hazard ratio (i.e., virulence) extracted for survival analysis in Fig. 2. The virulence correlated strongly with the speed of proliferation at the initiation of the infection. (D) Correlation between early growth in wild-type hosts of the bacterial strains with their early growth in the immunodeficient host. A solid line represents a perfect correlation (i.e., when the immune system does not affect the bacterial growth). Departure from the line (y = x) indicates a difference in proliferation when the host was immunodeficient. (E) Correlation between the effect of the immune system on proliferation (i.e., estimate of the interaction effect between time and genotype) and the hazard ratio. A dotted line represents the absence of difference between proliferation in immunodeficient hosts and in the healthy host. Values are the estimates extracted from the analysis in panel B. In all panels, blue represents wild-type strains and red represents lrp mutants. Colored triangles represent the mean per replicate.
- FIG 4
Bacterial load upon death (BLUD) estimated approximately 12 h to 30 h after injection in wild-type hosts. (A) Mutant strains reached the same BLUD as wild-type strains. Experiments were replicated with three different overnight bacterial cultures and fly batches. (B) Correlation between BLUD and hazard ratio. Mutant and wild-type strains reached the same BLUD, but wild-type strains had a higher hazard ratio and reached the BLUD about 10 h earlier, suggesting that lrp mutations affect virulence but not pathogenicity. Colored triangles represent the mean of the replicates.
- FIG 5
Proliferation during the second step of infection, within the dead host. (A) Proliferation between death and 24 h later in the wild-type host and (B) model estimate of growth postdeath (i.e., estimate of the parameter “time” in the model to analyze panel A). Unlike when the host was alive, lrp mutant strains had a higher density than wild-type strains when the host was dead. Missense mutation strains (light red) did not proliferate differently in dead hosts from nonsense mutation strains (dark red). Experiments were replicated with two (strains 23, 36, 42, and 51), three (strain 44), or four (strains 25, 29, and 40) different overnight bacterial cultures and fly batches.
- FIG 6
Trade-off between proliferation in the first and second steps of infection. The correlation between proliferation at the start of the infection and within the dead host is shown. While wild-type strains proliferated best at the initiation of the infection, they performed poorly in the dead host. Conversely, lrp mutant strains proliferated better in the dead host but lost the ability to proliferate rapidly at the initiation of the infection.
