Identification of Lactobacillus plantarum genes that are induced in the gastrointestinal tract of mice

Abstract

Lactobacillus plantarum is a flexible and versatile microorganism that inhabits a variety of environmental niches, including the human gastrointestinal (GI) tract. Moreover, this lactic acid bacterium can survive passage through the human or mouse stomach in an active form. To investigate the genetic background of this persistence, resolvase-based in vivo expression technology (R-IVET) was performed in L. plantarum WCFS1 by using the mouse GI tract as a model system. This approach identified 72 L. plantarum genes whose expression was induced during passage through the GI tract as compared to laboratory media. Nine of these genes encode sugar-related functions, including ribose, cellobiose, sucrose, and sorbitol transporter genes. Another nine genes encode functions involved in acquisition and synthesis of amino acids, nucleotides, cofactors, and vitamins, indicating their limited availability in the GI tract. Four genes involved in stress-related functions were identified, reflecting the harsh conditions that L. plantarum encounters in the GI tract. The four extracellular protein encoding genes identified could potentially be involved in interaction with host specific factors. The rest of the genes are part of several functionally unrelated pathways or encode (conserved) hypothetical proteins. Remarkably, a large number of the functions or pathways identified here have previously been identified in pathogens as being important in vivo during infection, strongly suggesting that survival rather than virulence is the explanation for the importance of these genes during host residence.

FIG. 1.

Basic principles of R-IVET. L. plantarum strain NZ7109 harbors a chromosomally located loxP-ery-loxP cassette and pNZ7125. Chromosomal loci of the L. plantarum genome (▴) are cloned upstream of cre in pNZ7125 and promoter activities in the resulting library can be trapped by monitoring the erythromycin phenotype, since cre expression will lead to excision of the erythromycin marker from the chromosome by a homologous recombination event between the two loxP sites. The colonies in the library appearing as erythromycin-resistant in the laboratory (no active promoters under laboratory conditions) were administered to mice, and changes in the erythromycin phenotype (promoter activations) were monitored in fecal samples.