Abstract
In certain conditions, members of the Lactobacillus genus are auxotrophs that have fastidious requirements for growth. Notably, Lactobacillus cannot grow in M9 medium, a minimal synthetic medium used for Escherichia coli. However, we found that some Lactobacillus strains can be grown in M9 when co-cultured with E. coli K-12. In the co-culture, L. casei proliferates exponentially, reaching cell densities of 108 CFU (colony-forming unit) ml−1 in 6 h and dominating E. coli in the late growth phase. Spent medium from E. coli grown overnight lacked this growth-promoting effect on L. casei. Similarly, the effect was not observed when the species were separated by a 0.4-µm membrane. Microscopic observations showed that L. casei are embedded in the micro-scale clusters of E. coli in the early growth phase. This study describes for the first time the ability of a Lactobacillus species to grow in minimal medium when in close proximity with co-cultured bacteria.
Highlights
In certain conditions, members of the Lactobacillus genus are auxotrophs that have fastidious requirements for growth
We found that the CFU values of 6 of the tested Lactobacillus strains, including 3 belonging to the L. casei-group and 3 strains of L. plantarum, increased in the presence of E. coli (Fig. 1)
This study demonstrated for the first time that lactic acid bacteria (LAB), which are strictly auxotrophic, can interact with co-cultured E. coli to proliferate in what would otherwise be nutrient-limiting conditions
Summary
Members of the Lactobacillus genus are auxotrophs that have fastidious requirements for growth. Some probiotic strains like L. rhamnosus, L. casei, and L. johnsonii potentially have therapeutic effects on chronic inflammatory bowel diseases[4,5] Despite such health-promoting and therapeutic relevance, information on the physiology of LAB is still lacking. It has been shown that lactobacilli employ multiple strategies for ecological adaptation, including amino acid transport[12], mucus adherence[17,18,19], adhesion to Peyer’s patches[20], and cell surface-associated proteinases[21,22]. Another ecological aspect of Lactobacillus auxotrophy is their inter-species interactions with other microbiota. NBRC 3831 with E. coli K-12, including the demonstration that E. coli fimbriae and lipopolysaccharide (LPS) are essential mediators of this interaction[28]
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