(A) In vitro growth of B. thai wild-type and a strain bearing gene deletions in all five T6SSs (ΔT6S). The data presented are an average of three replicates. (error bars smaller than symbols). (B) B. thai wild-type and ΔT6S swimming motility in semi-solid LB agar (scale bar = 1.0 cm). (C) Fluorescence images of growth competition assays between GFP-labeled B. thai wild-type and ΔT6S strains against the indicated unlabeled competitor species. Competition assay outcomes could be divided into T6S-independent (AR, Agrobacterium rhizogenes; ATu, A. tumefaciens; AV, A. vitis; PD, Paracoccus denitrificans; RS, Rhodobacter sphaeroides; ATe, Acidovorax temperans; BT, B. thailandensis; BV, B. vietnamiensis; AC, Acinetobacter calcoaceticus; AH, Aeromonas hydrophila; PAt, Pectobacterium atrosepticum; FN, Francisella novicida; PAe, Pseudomonas aeruginosa; SM, Serratia marcescens; VC, Vibrio cholerae; VP, Vibrio parahaemolyticus; VV, V. vulnificus; XC, Xanthomonas campestris; XN, Xenorhabdus nematophilus; YP, Yersinia pestis LCR–; BC, Bacillus cereus; BS, B. subtilis; ML, Micrococcus luteus; SA, Staphylococcus aureus; SP, Streptococcus pyogenes), those with modest T6S-effects (BA, B. ambifaria; EC, E. coli; KP, Klebsiella pneumoniae; ST, Salmonella typhimurium) and those in which B. thai proliferation was strongly T6S-dependent (dashed boxes – PP, P. putida E0044; PF, P. fluorescens ATCC27663; SP, S . proteamaculans 568). This latter group of organisms is referred to as the T6S-dependent competitors (TDCs).