This study analyzes the occurrence of bile salt hydrolase in fourteen strains belonging to the genus Bifidobacterium. Deconjugation activity was detected using a plate test, two-step enzymatic reaction and activity staining on a native polyacrylamide gel. Subsequently, bile salt hydrolases from B. pseudocatenulatum and B. longum subsp. suis were purified using a two-step chromatographic procedure. Biochemical characterization of the bile salt hydrolases showed that the purified enzymes hydrolyzed all of the six major human bile salts under the pH and temperature conditions commonly found in the human gastrointestinal tract. Next, the dynamic rheometry was applied to monitor the gelation process of deoxycholic acid under different conditions. The results showed that bile acids displayed aqueous media gelating properties. Finally, gel-forming abilities of bifidobacteria exhibiting bile salt hydrolase activity were analyzed. Our investigations have demonstrated that the release of deconjugated bile acids led to the gelation phenomenon of the enzymatic reaction solution containing purified BSH. The presented results suggest that bile salt hydrolase activity commonly found among intestinal microbiota increases hydrogel-forming abilities of certain bile salts. To our knowledge, this is the first report showing that bile salt hydrolase activity among Bifidobacterium is directly connected with the gelation process of bile salts. In our opinion, if such a phenomenon occurs in physiological conditions of human gut, it may improve bacterial ability to colonize the gastrointestinal tract and their survival in this specific ecological niche.
SummarySuccinic acid is an important C4‐building chemical platform for many applications. A novel succinic acid‐producing bacterial strain was isolated from goat rumen. Phylogenetic analysis based on the 16S rRNA sequence and physiological analysis indicated that the strain belongs to the genus Enterobacter. This is the first report of a wild bacterial strain from the genus Enterobacter that is capable of efficient succinic acid production. Co‐fermentation of glycerol and lactose significantly improved glycerol utilization under anaerobic conditions, debottlenecking the utilization pathway of this valuable biodiesel waste product. Succinic acid production reached 35 g l−1 when Enterobacter sp. LU1 was cultured in medium containing 50 g l−1 of glycerol and 25 g l−1 of lactose as carbon sources.
Background: Members of the genus Bifidobacterium are anaerobic Gram-positive Actinobacteria, which are natural inhabitants of human and animal gastrointestinal tract. Certain bifidobacteria are frequently used as food additives and probiotic pharmaceuticals, because of their various health-promoting properties. Due to the enormous demand on probiotic bacteria, manufacture of high-quality products containing living microorganisms requires rapid and accurate identification of specific bacteria. Additionally, isolation of new industrial bacteria from various environments may lead to multiple isolations of the same strain, therefore, it is important to apply rapid, low-cost and effective procedures differentiating bifidobacteria at the intra-species level. The identification of new isolates using microbiological and biochemical methods is difficult, but the accurate characterization of isolated strains may be achieved using a polyphasic approach that includes classical phenotypic methods and molecular procedures. However, some of these procedures are time-consuming and cumbersome, particularly when a large group of new isolates is typed, while some other approaches may have too low discriminatory power to distinguish closely related isolates obtained from similar sources.
Response surface methodology was used to optimize media components such as carbon and nitrogen (simple and complex) sources, mineral agents and growth factors (B vitamins, amino acids) for enhancing the biomass production of Lactobacillus rhamnosus PEN. For screening experiment the following carbon sources were selected: glucose, glucose+pyruvate, glucose+citrate, glucose+lactate, galactose, fructose, lactose, sucrose, maltose, lactulose, fructooligosaccharides, maltodextrins DP 4-7 and DP 13-17. Nitrogen sources such as yeast extract, meat extract and peptone K were used in lower concentrations than in MRS medium which served as a control. All experiments were run at 37 degrees C for 24-48 h under stationary conditions. Constituents chosen after the first screening experiments were further screened by the Plackett-Burman design. Glucose and sodium pyruvate, meat extract, potassium phosphate, sodium acetate, and ammonium citrate were chosen as promising medium components for further optimization studies. By solving the regression equation and analyzing the response surface carton, optimal concentrations of the components were determined as: glucose (13.4 g/l), sodium pyruvate (3.4 g/l), meat extract (7.2 g/l), potassium phosphate (2.0 g/I), sodium acetate (5.0 g/1) and ammonium citrate (2.0 g/l). In comparison to MRS broth the optimal medium contained fewer ingredients and in modified amounts but Lb. ihamnosus PEN showed better growth activity. Biomass concentration (as dry cell weight) of bacteria cultivated in optimal medium at bioreactor conditions was 5.5 g/l after 16 h of incubation, being higher in comparison with bacterial growth in MRS medium (1.9 g/l) under the same conditions. Moreover, the new medium was less expensive.
The central composite design was developed to search for an optimal medium for the growth of Lactobacillus rhamnosus OXY. The effect of various media components, such as carbon sources, simple and complex nitrogen sources, mineral agents, and growth factors (vitamins B, amino acids) was examined. The first-order model based on Plackett-Burman design showed that glucose, sodium pyruvate, meat extract and mineral salts significantly influenced the growth of the examined bacteria. The second-order polynomial regression confirmed that maximum biomass production could be achieved by the combination of glucose (12.38 g/l), sodium pyruvate (3.15 g/l), meat extract (4.08 g/l), potassium phosphate (1.46 g/l), sodium acetate (3.65 g/l) and ammonium citrate (1.46 g/l). The validation of the predicted model carried out in bioreactor conditions confirmed the usefulness of the new medium for the culture of L. rhamnosus OXY in large scale. The optimal medium makes the culture of the probiotic bacterium L. rhamnosus OXY more cost effective.
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