Aims:  To characterize the adhesion molecule of Lactobacillus plantarum LA 318 that shows high adhesion to human colonic mucin (HCM). Methods and Results:  The adhesion test used the BIACORE assay where PBS‐washed bacterial cells showed a significant decrease in adherence to HCM than distilled water‐washed cells. A component in the PBS wash fraction adhered to the HCM and a main protein was detected as a c. 40‐kDa band using SDS‐PAGE. Using homology comparisons of the N‐terminal amino acid sequences compared with sequence databases, this protein was identified as glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH). The DNA sequence of LA 318 GAPDH was 100% identical to the GAPDH (gapB) of L. plantarum WCFS1. The purified GAPDH adhered to HCM. Conclusions:  We found the adhesin of L. plantarum LA 318 to HCM in its culture PBS wash fraction. The molecule was identified as GAPDH. Because LA 318 possesses the same adhesin as many pathogens, the lactobacilli GAPDH may compete with pathogens infecting the intestine. Significance and Impact of the Study:  This is the first report showing GAPDH expressed on the cell surface of lactobacilli adheres to mucin suggesting L. plantarum LA 318 adheres to HCM using GAPDH binding activity to colonize the human intestinal mucosa.

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In addition to functioning as detergents that aid digestion of dietary lipids in the intestine, some bile acids have been shown to exhibit antimicrobial activity. However, detailed information on the bactericidal activities of the diverse molecular species of bile acid in humans and rodents is largely unknown. Here, we investigated the toxicity of 14 typical human and rodent free bile acids (FBAs) by monitoring intracellular pH, membrane integrity, and viability of a human intestinal bacterium, Japan Collection of Microorganisms (JCM) 1192, upon exposure to these FBAs. Of all FBAs evaluated, deoxycholic acid (DCA) and chenodeoxycholic acid displayed the highest toxicities. Nine FBAs common to humans and rodents demonstrated that α-hydroxy-type bile acids are more toxic than their oxo-derivatives and β-hydroxy-type epimers. In five rodent-specific FBAs, β-muricholic acid and hyodeoxycholic acid showed comparable toxicities at a level close to DCA. Similar trends were observed for the membrane-damaging effects and bactericidal activities to JCM 1395 and DSM 2079, commonly represented in the human and rodent gut microbiota. These findings will help us to determine the fundamental properties of FBAs and better understand the role of FBAs in the regulation of gut microbiota composition.

Polyether metabolites are an important class of natural products. Although their biosynthesis, especially construction of polyether skeletons, attracted organic chemists for many years, no experimental data on the enzymatic polyether formation has been obtained. In this study, a putative epoxide hydrolase gene lsd19 found on the biosynthetic gene cluster of an ionophore polyether lasalocid was cloned and successfully overexpressed in Escherichia coli. Using the purified Lsd19, a proposed substrate, bisepoxyprelasalocid, and its synthesized analogue were successfully converted into lasalocid A and its derivative via a 6-endo-tet cyclization mode. On the other hand, treatment of the bisepoxide with trichloroacetic acid gave isolasalocid A via a 5-exo-tet cyclization mode. Therefore, the enzymatic conversion observed in this study unambiguously showed that the bisepoxyprelasalocid is an intermediate of the lasalocid biosynthesis and that Lsd19 catalyzes the sequential cyclic ether formations involving an energetically disfavored 6-endo-tet cyclization. This is the first example of the enzymatic epoxide-opening reactions leading to a polyether natural product.

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