Contribution of glutamate decarboxylase in <it>Lactobacillus reuteri</it> to acid resistance and persistence in sourdough fermentation

Abstract Background Acid stress impacts the persistence of lactobacilli in industrial sourdough fermentations, and in intestinal ecosystems. However, the contribution of glutamate to acid resistance in lactobacilli has not been demonstrated experimentally, and evidence for the contribution of acid resistance to the competitiveness of lactobacilli in sourdough is lacking. It was therefore the aim of this study to investigate the ecological role of glutamate decarboxylase in L. reuteri. Results A gene coding for a putative glutamate decarboxylase, gadB, was identified in the genome of L. reuteri 100-23. Different from the organization of genetic loci coding for glutamate decarboxylase in other lactic acid bacteria, gadB was located adjacent to a putative glutaminase gene, gls3. An isogenic deletion mutant, L. reuteri ∆gadB, was generated by a double crossover method. L. reuteri 100-23 but not L. reuteri ∆gadB converted glutamate to γ-aminobutyrate (GABA) in phosphate butter (pH 2.5). In sourdough, both strains converted glutamine to glutamate but only L. reuteri 100-23 accumulated GABA. Glutamate addition to phosphate buffer, pH 2.5, improved survival of L. reuteri 100-23 100-fold. However, survival of L. reuteri ∆gadB remained essentially unchanged. The disruption of gadB did not affect growth of L. reuteri in mMRS or in sourdough. However, the wild type strain L. reuteri 100-23 displaced L. reuteri ∆gadB after 5 cycles of fermentation in back-slopped sourdough fermentations. Conclusions The conversion of glutamate to GABA by L. reuteri 100-23 contributes to acid resistance and to competitiveness in industrial sourdough fermentations. The organization of the gene cluster for glutamate conversion, and the availability of amino acids in cereals imply that glutamine rather than glutamate functions as the substrate for GABA formation. The exceptional coupling of glutamine deamidation to glutamate decarboxylation in L. reuteri likely reflects adaptation to cereal substrates.</p

Children at Risk of Poor Educational Outcomes: In Search of a Transdisciplinary Theoretical Framework

In most western countries, the number of \u27children at risk\u27 for poor educational outcomes seems to have been increased in recent years. Nearly 20 % of the students in those countries meanwhile fail to acquire the levels of literacy, mathematics and science achievement that are required to effectively participate in today\u27s knowledge-based society. Thus, there is a strong need to extend research focusing on the identification of risk factors associated with these undesired educational outcomes in children. Although attempts have been made to conceptualize the issue of \u27children at risk\u27 for poor educational outcomes from the perspective of different scientific disciplines, the interplay of multiple risk factors located on the different levels focused by different disciplines has been rarely addressed. Thus, we advocate for more transdisciplinary activities integrating multiple scientific perspectives on the concept of \u27children at risk\u27 for poor educational outcomes. These activities should include at least three dimensions affecting developmental trajectories being important for children\u27s individual academic outcomes: (1) individual characteristics including both biological as well as psychological features, (2) contextual factors, as well as dynamics defined by (3) time changes and interactions between individual and contextual categories of risk factors. (DIPF/Orig.