L. plantarum-monoassociated fly guts have low numbers of intestinal progenitor cells. (A to C) Immunofluorescence of posterior midguts of CR (A), GF (B), and L. plantarum-monoassociated (C) flies at day 11 of age. Bars, 25 µm. (D to F) Immunofluorescence of posterior midguts of CR (D), GF (E), and L. plantarum-monoassociated (F) flies at day 26 of age. Bars, 10 µm. Guts were stained with Hoechst stain and anti-Armadillo/Prospero antibodies as indicated. Progenitor cells were visualized with GFP as indicated. Hoechst stain (blue), GFP (green), and anti-Armadillo/Prospero (red) were merged in the fourth and eighth rows. (G) Quantification of progenitor numbers per unit surface area at day 26 of age. P values are the results of pairwise comparisons from a one-way ANOVA. (H) Mean midgut length of CR, GF, and L. plantarum-monoassociated flies at day 15 postinoculation. n.s., not significant.