Artisanal and farmer bread making practices differently shape fungal species community composition in French sourdoughs

Preserving microbial diversity in food systems is one of the many challenges to be met to achieve food security and quality. Although industrialization led to the selection and spread of specific fermenting microbial strains, there are still ongoing artisanal processes that may allow the conservation of a wider species diversity and genetic diversity. We examined whether the diversity of artisanal practices could lead to an increased level in fungal species diversity for bread making. We used an interdisciplinary participatory research approach including bakers, psycho-sociologists and microbiologists to analyze French bread making practices and describe fungal communities in naturally fermented sourdough of 27 bakers and 12 farmer bakers. Bread making practices were classified in two groups: the farmer-like practice group and the artisanal-like practice group. The well-known bakery yeast, Saccharomyces cerevisiae, was dominant (i.e. with a relative abundance over 50%) in only 24% of sourdoughs while other yeast species, belonging to the Kazachstania genus, were dominant in 54% of sourdoughs. Bread making practices were found to drive the distribution of fungal species across sourdoughs. The most striking bread making practice effect was the occurrence of Kazachstania humilis in sourdoughs made with artisanal-like practices and the occurrence of Kazachstania bulderi in sourdoughs made with farmer-like practices. Phenotypic divergences between sourdough and non-sourdough strains were found for K. humilis but not for K. bulderi. Overall, our results showed that preserving bread making practice diversity allows the preservation of a higher species and phenotypic diversity in microbial communities

Concentration-dependent reversible activation-inhibition of human butyrylcholinesterase by tetraethylammonium ion

International audienceTetraalkylammonium (TAA) salts are well known reversibleinhibitors of cholinesterases. However, at concentrationsaround 10 mM, they have been found to activate thehydrolysis of positively charged substrates, catalyzed bywild-type human butyrylcholinesterase (EC 3.1.1.8)[Erdoes,E.G., Foldes, F.F., Zsigmond, E.K., Baart, N. & Zwartz,J.A. (1958) Science 128, 92]. The present study was undertaken to determine whether the peripheral anionic site (PAS)of human BuChE (Y332, D70) and/or the catalytic substratebinding site (CS) (W82, A328) are involved in this phenomenon. For this purpose, the kinetics of butyrylthiocholine(BTC) hydrolysis by wild-type human BuChE, by selectedmutants and by horse BuChE was carried out at 25 °C andpH 7.0 in the presence of tetraethylammonium (TEA). Itappears that human enzymes with more intact structure ofthe PAS show more prominent activation phenomenon. Thefollowing explanation has been put forward: TEA competeswith the substrate at the peripheral site thus inhibiting thesubstrate hydrolysis at the CS. As the inhibition by TEA isless effective than the substrate inhibition itself, it mimicsactivation. At the concentrations around 40 mM, well withinthe range of TEA competition at both substrate binding sites,it lowers the activity of all tested enzymes

Contribution of the active-site metal cation to the catalytic activity and to the conformational stability of phosphotriesterase: temperature- and pH-dependence.

Phosphotriesterase (PTE) detoxifies nerve agents and organophosphate pesticides. The two zinc cations of the PTE active centre can be substituted by other transition metal cations without loss of activity. Furthermore, metal-substituted PTEs display differences in catalytic properties. A prerequisite for engineering highly efficient mutants of PTE is to improve their thermostability. Isoelectric focusing, capillary electrophoresis and steady-state kinetics analysis were used to determine the contribution of the active-site cations Zn2+, Co2+ or Cd2+ to both the catalytic activity and the conformational stability of the corresponding PTE isoforms. The three isoforms have different pI values (7.2, 7.5 and 7.1) and showed non-superimposable electrophoretic titration curves. The overall structural alterations, causing changes in functional properties, were found to be related to the nature of the bound cation: ionic radius and ion electronegativity correlate with Km and kcat respectively. In addition, the pH-dependent activity profiles of isoforms were different. The temperature-dependent profiles of activity showed maximum activity at T < or =35 degrees C, followed by an activation phase near 45-48 degrees C and then inactivation which was completed at 60 degrees C. Analysis of thermal denaturation of the PTEs provided evidence that the activation phase resulted from a transient intermediate. Finally, at the optimum activity between pH 8 and 9.4, the thermostability of the different PTEs increased as the pH decreased, and the metal cation modulated stability (Zn2+-, Co2+- and Cd2+-PTE showed different T (m) values of 60.5-67 degrees C, 58-64 degrees C and 53-64 degrees C respectively). Requirements for optimum activity of PTE (displayed by Co2+-PTE) and maximum stability (displayed by Zn2+-PTE) were demonstrated