Klebsiella pneumoniae T6SS exacerbates gut inflammation promoting tumorigenesis.

Fragkoulis, K.; Uusi-Makela, M. I.; Sanz, G.; Williams, C.; Schuppe-Koistinen, I.; Gustafsson, U. O.; Engstrand, L.; Normark, S.; Henriques-Normark, B.; Hayer, J.; Peuget, S.; Aschtgen, M.-S.

doi:10.64898/2026.03.31.715367

bioRxiv · 10.64898/2026.03.31.715367

Klebsiella pneumoniae T6SS exacerbates gut inflammation promoting tumorigenesis.

Fragkoulis, K.·Uusi-Makela, M. I.·Sanz, G.·Williams, C.·Schuppe-Koistinen, I.·Gustafsson, U. O.·Engstrand, L.·Normark, S.·Henriques-Normark, B.·Hayer, J.·Peuget, S.·Aschtgen, M.-S.

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Abstract

Dysbiosis and bacterial pathobionts contribute to inflammation in IBD and CRC, yet the molecular drivers of this process remain unclear. We identify the Klebsiella pneumoniae type VI secretion system (T6SS) as a key promoter of intestinal inflammation and tumor progression. Metagenomic analyses revealed enrichment of T6SS encoding genes in the gut microbiota of IBD patients during inflammatory flares. In zebrafish and mouse models, K. pneumoniae T6SS activity exacerbated inflammation and promoted colorectal tumor growth. Mechanistically, T6SS firing enhanced the secretion of LPS via outer membrane vesicles (OMVs), driving NF-{kappa}B activation and interferon signalling in host cells. In vivo, T6SS-dependent inflammation was associated with the expansion of regulatory T-cell subsets and an immunosuppressive tumor microenvironment. These findings redefine the T6SS as a microbial determinant of host inflammation and cancer progression, highlighting T6SS inhibition as a potential therapeutic approach for IBD and CRC. HighlightsO_LIT6SS-encoding Enterobacteria are enriched in the gut microbiota of IBD patients C_LIO_LIKlebsiella pneumoniae T6SS exacerbates colitis in mice C_LIO_LIT6SS activity enhances outer membrane vesicle secretion and LPS release C_LIO_LIT6SS promotes colorectal tumorigenesis and immune dysregulation C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=186 HEIGHT=200 SRC="FIGDIR/small/715367v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1c99341org.highwire.dtl.DTLVardef@e2d0eborg.highwire.dtl.DTLVardef@1021387org.highwire.dtl.DTLVardef@1502c97_HPS_FORMAT_FIGEXP M_FIG C_FIG

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Fragkoulis, K., Uusi-Makela, M. I., Sanz, G., Williams, C., Schuppe-Koistinen, I., Gustafsson, U. O., Engstrand, L., Normark, S., Henriques-Normark, B., Hayer, J., Peuget, S., Aschtgen, M.-S.. 2026-03-31. Klebsiella pneumoniae T6SS exacerbates gut inflammation promoting tumorigenesis.. https://doi.org/10.64898/2026.03.31.715367

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