Fig. 2

Figure 2. Loss of spdE enables rapid immigration into hosts and fish-to-fish transmission

(A) Competitive indices (CI) of ancestral Aer01 (WT^anc), an evolved isolate (L3_P10), ΔspdE, the WT overexpressing spdE (WT^anc_OE), ΔspdE complemented with WT copy of spdE (ΔspdE_comp), and ΔspdE complemented with an evolved mutant allele (ΔspdE_comp^evol). All strains were competed against a WT reference strain (see Figure S1A). Points outlined in red represent a lower or upper bound for the actual CI (see STAR Methods). Dotted line indicates CI of 1 (i.e., no competitive advantage). n ≥ 8 fish/condition, one experimental replicate. Inset graph presents CI data for Aer01 mutants in the flask medium (a single point for each flask); y axis and symbols match the main graph.

(B) Competitive indices of ΔspdE and L3_P10 evolved isolate are dependent on mode of inoculation (flask medium [FM inoc.] versus gavage). Dotted line indicates CI of 1 (i.e., no competitive advantage). n ≥ 6 fish/condition, one experimental replicate.

(C) Immigration rates of ancestral Aer01, ΔspdE, and the L3_P10 mono-associated into larval fish (see STAR Methods and Figure S3A) (n = 3 experimental replicates per time point). Means (± SEM) are plotted.

(D) Fish-to-fish transmission of ancestral Aer01 (WT^anc) and ΔspdE. Mono-associated “donor” fish were added to a flasks of GF “recipient” fish for 15 h, then abundances of Aer01 in all fish were determined. n ≥ 27 fish/condition, two experimental replicates. p value < 0.0001, two-tailed Mann-Whitney test. CFU/gut, colony-forming units per gut. Median and interquartile ranges are plotted in (A, B, and D). See also Figure S2.