Utilization of sludge derived from landfill leachate treatment as a source of nutrients for the growth of Nicotiana alata L.

The sludges derived from the leachate treatment (LS) represent an important environmental and operational problem in the landfill management. On the other hand, they can be utilized as an alternative source of nutrients and organic matter. The main objective of this work was to evaluate the reuse of the LS of a sanitary landfill in Santa Fe city - Argentina, as an organic amendment for the development of Nicotiana alata L. plants. Different doses of LS were applied to a soil mixture for potted seedling growth. The response surface methodology was applied, using a one-factor design. Once the phenological stage of flowering began, the plants were harvested. Physiological and biochemical determinations were made in order to evaluate the effects of the different amendments. Application of LS notably improved growth parameters such as stem height, leaf area and dry matter. Additionally, the content of proteins and photosynthetic pigments was enhanced. Through the multiple regression statistical analyses, the relationship between the response variables and the sludge content was established. The multivariate optimization analysis yielded 53% as the optimal sludge content. Our results indicate that this sludge, in appropriate doses, can be used as an organic amendment for the revegetation of sanitary landfills.

Biochemical Characterization of Heat-Tolerant Recombinant L-Arabinose Isomerase from Enterococcus faecium DBFIQ E36 Strain with Feasible Applications in D-Tagatose Production.

D-Tagatose is a ketohexose, which presents unique properties as a low-calorie functional sweetener possessing a sweet flavor profile similar to D-sucrose and having no aftertaste. Considered a generally recognized as safe (GRAS) substance by FAO/WHO, D-tagatose can be used as an intermediate for the synthesis of other optically active compounds as well as an additive in detergent, cosmetic, and pharmaceutical formulations. This study reports important features for L-arabinose isomerase (EC 5.3.1.4) (L-AI) use in industry. We describe arabinose (araA) gene virulence analysis, gene isolation, sequencing, cloning, and heterologous overexpression of L-AI from the food-grade GRAS bacterium Enterococcus faecium DBFIQ E36 in Escherichia coli and assess biochemical properties of this recombinant enzyme. Recombinant L-AI (rL-AI) was one-step purified to homogeneity by Ni2+-agarose resin affinity chromatography and biochemical characterization revealed low identity with both thermophilic and mesophilic L-AIs but high degree of conservation in residues involved in substrate recognition. Optimal conditions for rL-AI activity were 50 °C, pH 5.5, and 0.3 mM Mn2+, exhibiting a low cofactor concentration requirement and an acidic optimum pH. Half-life at 45 °C and 50 °C were 1427 h and 11 h, respectively, and 21.5 h and 39.5 h at pH 4.5 and 5.6, respectively, showing the high stability of the enzyme in the presence of a metallic cofactor. Bioconversion yield for D-tagatose biosynthesis was 45% at 50 °C after 48 h. These properties highlight the technological potential of E. faecium rL-AI as biocatalyst for D-tagatose production.