Exopolysaccharides May Increase Gastrointestinal Stress Tolerance of Lactobacillus reuteri

This study investigated a possible relationship between exopolysaccharides (EPS) production and the resistance to bile salts and low pH in intestinal strains of Lactobacillus reuteri. The strains displayed a mucoid phenotype, when grown in the presence of 10 % sucrose. Scanning electron microscopy (SEM) revealed strands of exopolysaccharide linking neighbouring cells. The strains (except L. reuteri B1/1) produced EPS in the range from 15.80 to 650.70 mg.l−1. The strains were tested for tolerance to bile salts (0.15; 0.3 %) and low pH (1.5—2.0—2.5—3.0). The survival rate, after the treatment with artificial gastric and intestinal juices, was determined by flow cytometric analysis. The strains of L. reuteri that produced 121—650 mg.l−1 of EPS showed a significantly higher tolerance (P < 0.001) to the gastric juice at pH 3 and 2.5, throughout the entire exposure time, in comparison to the strains that produced less than 20 mg.l−1 of EPS. L. reuteri L26, with the highest production of EPS, exhibited the highest survival rate (60 %) at pH 2 after the 120 minutes of in-cubation and was able to tolerate pH 1.5 for 30 minutes. Higher production of EPS significantly (P < 0.001) increased the strains’ tolerance against the intestinal juice in the presence of 0.15 and 0.3 % bile salts and was time dependent. L. reuteri L26 showed the highest tolerance (P < 0.001) against 0.3 % bile salts. This investigation revealed a positive correlation between the EPS production and the resistance of intestinal L. reuteri to the stress conditions of the gastrointestinal tract (GIT)

How do social status and tree architecture influence radial growth, wood density and drought response in spontaneously established oak forests?

AbstractKey messageDuring the past decades, a multitude of oak stands have spontaneously established across the pine-dominated landscapes of the French Landes de Gascogne. Yet their future performance under modern climate change is unknown. We show that coppiced, dominant trees are most prepared to cope with drought episodes, displaying higher basal area increment and lower sensitivity to extreme events.ContextForest stands dominated by pedunculate oak (Quercus robur L.) have spontaneously established across the pine-dominated landscapes of the French Landes de Gascogne. These oak stands are typically unmanaged and unsystematically coppiced, resulting in mixtures of single- and multi-stemmed (coppiced) trees.AimsTo determine the ability of spontaneous oak forest stands to face climate change–related hazards, by analysing differences in growth (tree-ring width and basal area increment—BAI), wood density and climate sensitivity depending on their tree architecture (single- vs multi-stemmed trees) and their social status in the forest.MethodsWe exhaustively cored 15 oak stands (n = 657 trees). We compared stand characteristics and climate sensitivity between tree architectures considering two sampling designs, either all sampled trees (the exhaustive sampling) or those with a dominant status (dominant sampling). At the tree level, we used linear mixed effects models to compare wood density and growth between tree architectures and the trees’ social status within the canopy layer (dominant- vs non-dominant trees).ResultsMulti-stemmed trees exhibited higher wood density than single-stemmed trees for diameters > 30 cm. Dominant multi-stemmed trees showed lower sensitivity to extreme events (pointer years), higher BAI but lower annual growth rates than dominant single-stemmed trees.ConclusionDominant multi-stemmed trees are potentially the most prepared ones to cope with increasing soil water deficit following drought episodes, at least during the first 60 years of the life of the tree. The vulnerability to face harsher climate conditions for Q. robur stands can be misled when using a dominant sampling design