Fig. 4: Group I capsule protect commensal Klebsiella isolates against V. cholerae’s T6SS attacks.

a In silico identification of capsular genes in the commensal collection. Enterobacteriaceae-specific capsule groups (ABC, IVe, IVs, I, colanic acid synthesis) are shown. The blue heatmap (on the left) shows the relative survival values of the T6SS-attacked commensals with 0 and 100 being defined as the lowest and highest log-transformed CFU/ml numbers, respectively (according to the data provided in Fig. 1a–j). Commensal strain numbers and the color code (on the right) are as defined in Fig. 1. b The production of group I capsules by the Klebsiella gut commensal isolates was assessed by quantification of the strains’ uronic acid content. c, d Deletion of capsule biosynthesis genes renders commensal Klebsiella sensitive to T6SS-mediated intoxication. Representative WT and wza-negative Klebsiella mutants (commensal K. oxytoca #16 and K. pneumoniae #19) were tested for survival in the presence of T6SS+ (WT; plain bars) or T6SS− (ΔvipA; stripped bars) V. cholerae (panel c) or against diverse T6SS-positive (plain bar) and T6SS-negative (stripped bar) pathogens (panel d; V. cholerae [V.c.], E. cloacae [E.cl.; commensal #10], or A. baumannii [A.b.; strain A118]). Values are derived from three independent experiments and the bars represent the mean (±SD, as defined by the error bars). dl, detection limit, as indicated by the dashed line. For panels c and d, significant differences between samples containing T6SS+ and T6SS− predators were determined using a two-sided Student’s t-test corrected for multiple comparisons. Only significant differences are indicated. *p < 0.05; ***p < 0.001. Source data underlying all panels are provided in the Source data file.