Strain-specific diversity of mucus-binding proteins in the adhesion and aggregation properties of Lactobacillus reuteri.
Mucus-binding proteins (MUBs) have been revealed as one of the effector molecules involved in mechanisms of the adherence of lactobacilli to the host; mub, or mub-like, genes are found in all of the six genomes of Lactobacillus reuteri that are available. We recently reported the crystal structure of a Mub repeat from L. reuteri ATCC 53608 (also designated strain 1063), revealing an unexpected recognition of immunoglobulins. In the current study, we explored the diversity of the ATCC 53608 mub gene, and MUB expression levels in a large collection of L. reuteri strains isolated from a range of vertebrate hosts. This analysis revealed that the MUB was only detectable on the cell surface of two highly related isolates when using antibodies that were raised against the protein. There was considerable variation in quantitative mucus adhesion in vitro among L. reuteri strains, and mucus binding showed excellent correlation with the presence of cell-surface ATCC 53608 MUB. ATCC 53608 MUB presence was further highly associated with the autoaggregation of L. reuteri strains in washed cell suspensions, suggesting a novel role of this surface protein in cell aggregation. We also characterized MUB expression in representative L. reuteri strains. This analysis revealed that one derivative of strain 1063 was a spontaneous mutant that expressed a C-terminally truncated version of MUB. This frameshift mutation was caused by the insertion of a duplicated 13&emsp14;nt sequence at position 4867&emsp14;nt in the mub gene, producing a truncated MUB also lacking the C-terminal LPxTG region, and thus unable to anchor to the cell wall. This mutant, designated 1063N (mub-4867(i)), displayed low mucus-binding and aggregation capacities, further providing evidence for the contribution of cell-wall-anchored MUB to such phenotypes. In conclusion, this study provided novel information on the functional attributes of MUB in L. reuteri, and further demonstrated that MUB and MUB-like proteins, although present in many L. reuteri isolates, show a high genetic heterogeneity among strains.
MacKenzie
Donald A
DA
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Jeffers
Faye
F
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Parker
Mary L
ML
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Vibert-Vallet
Amandine
A
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Bongaerts
Roy J
RJ
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Roos
Stefan
S
Department of Microbiology, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden.
Walter
Jens
J
Department of Food Science and Technology, University of Nebraska, Lincoln, NE, USA.
Juge
Nathalie
N
Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
D000818:Animals; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D016368:Frameshift Mutation; D052200:Limosilactobacillus reuteri / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009093:Mucus / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013045:Species Specificity
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008565:Membrane Proteins