D-Alanine-Controlled Transient Intestinal Mono-Colonization with Non-Laboratory-Adapted Commensal E. coli Strain HS

Cuenca Vera, Miguelangel; Pfister, Simona; Buschor, Stefanie; Bayramova, Firuza; Hernandez, Sara B.; Cava, Felipe; Kuru, Erkin; Van Nieuwenhze, Michael S.; Brun, Yves V.; Matos Coelho, Fernanda; Hapfelmeier, Siegfried Hektor (2016). D-Alanine-Controlled Transient Intestinal Mono-Colonization with Non-Laboratory-Adapted Commensal E. coli Strain HS. PLoS ONE, 11(3), e0151872. Public Library of Science 10.1371/journal.pone.0151872

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Soon after birth the mammalian gut microbiota forms a permanent and collectively highly resilient consortium. There is currently no robust method for re-deriving an already micro- bially colonized individual again-germ-free. We previously developed the in vivo growth- incompetent E. coli K-12 strain HA107 that is auxotrophic for the peptidoglycan components D-alanine (D-Ala) and meso-diaminopimelic acid (Dap) and can be used to transiently asso- ciate germ-free animals with live bacteria, without permanent loss of germ-free status. Here we describe the translation of this experimental model from the laboratory-adapted E. coli K-12 prototype to the better gut-adapted commensal strain E. coli HS. In this genetic back- ground it was necessary to complete the D-Ala auxotrophy phenotype by additional knock- out of the hypothetical third alanine racemase metC. Cells of the resulting fully auxotrophic strain assembled a peptidoglycan cell wall of normal composition, as long as provided
with D-Ala and Dap in the medium, but could not proliferate a single time after D-Ala/Dap removal. Yet, unsupplemented bacteria remained active and were able to complete their cell cycle with fully sustained motility until immediately before autolytic death. Also in vivo, the transiently colonizing bacteria retained their ability to stimulate a live-bacteria-specific intestinal Immunoglobulin (Ig)A response. Full D-Ala auxotrophy enabled rapid recovery to again-germ-free status. E. coli HS has emerged from human studies and genomic analyses as a paradigm of benign intestinal commensal E. coli strains. Its reversibly colonizing deriv- ative may provide a versatile research tool for mucosal bacterial conditioning or compound delivery without permanent colonization.

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