Competitiveness of reutericyclin producing and nonproducing Limosilactobacillus reuteri in food and intestinal ecosystems: a game of rock, paper, and scissors?

The ecological relationships among antimicrobial producing, resistant, and sensitive strains have been proposed to follow rock-paper-scissors dynamics, but evidence is mainly based on Gram-negative bacteriocins in vitro. The ecological relevance of antimicrobials in vivo or in situ has not been systematically studied. This study therefore aimed to analyze binary and ternary competitions among reutericyclin-producing strain Limosilactobacillus reuteri TMW1.656, its reutericyclin-resistant, nonproducing isogenic derivative L. reuteri TMW1.656ΔrtcN, and the reutericyclin-sensitive, nonproducing L. reuteri TMW1.656ΔrtcNΔrtcT in vitro (liquid culture and static plate), in situ (sourdough fermentation), and in vivo (gut of germ-free mice). In liquid culture, L. reuteri TMW1.656 had a higher fitness than TMW1.656ΔrtcN and TMW1.656ΔrtcNΔrtcT. Limosilactobacillus reuteri TMW1.656ΔrtcNΔrtcT had a higher fitness than TMW1.656ΔrtcN. On agar plates, L. reuteri TMW1.656 had a higher fitness than TMW1.656ΔrtcNΔrtcT. In situ, reutericyclin production and resistance had no influence on the fitness of the strains. In vivo, TMW1.656 had an advantage over TMW1.656ΔrtcN and TMW1.656ΔrtcNΔrtcT. Ternary competitions showed reutericyclin production was ecologically beneficial in all ecosystems. The findings support the ecological importance of reutericyclin in a variety of environments/niches, providing an explanation for the acquisition of the reutericyclin gene cluster in L. reuteri and its contribution to the ecological fitness of Streptococcus mutans.