FIG 4.

T6SS-deficient Serratia marcescens strains do not differ from the WT strain in fitness within the bee gut. Percentages of sampled bees infected with S. marcescens (top) and abundance of S. marcescens in the midguts and hindguts of individuals (bottom) 1 to 4 days after exposure are shown. MF bees were exposed to WT S. marcescens (A) or to SmE1E2 (B). Conventionalized (CV) bees were exposed to WT S. marcescens (C) or to SmE1E2 (D). Bees were exposed to 4 × 10⁸ S. marcescens cells/ml in sugar syrup for 1 day. Abundance was quantified by counting CFU. Box and whisker plots show range, first and third quartiles, and median. *, P < 0.05; **, P < 0.005, Kruskal-Wallis test with Dunn’s multiple-comparison test.