Structural Factors That Determine the Activity of the Xenobiotic Reductase B Enzyme from Pseudomonas putida on Nitroaromatic Compounds.

Xenobiotic reductase B (XenB) catalyzes the reduction of the aromatic ring or nitro groups of nitroaromatic compounds with methyl, amino or hydroxyl radicals. This reaction is of biotechnological interest for bioremediation, the reuse of industrial waste or the activation of prodrugs. However, the structural factors that explain the binding of XenB to different substrates are unknown. Molecular dynamics simulations and quantum mechanical calculations were performed to identify the residues involved in the formation and stabilization of the enzyme/substrate complex and to explain the use of different substrates by this enzyme. Our results show that Tyr65 and Tyr335 residues stabilize the ligands through hydrophobic interactions mediated by the aromatic rings of these aminoacids. The higher XenB activity determined with the substrates 1,3,5-trinitrobenzene and 2,4,6-trinitrotoluene is consistent with the lower energy of the highest occupied molecular orbital (LUMO) orbitals and a lower energy of the homo orbital (LUMO), which favors electrophile and nucleophilic activity, respectively. The electrostatic potential maps of these compounds suggest that the bonding requires a large hydrophobic region in the aromatic ring, which is promoted by substituents in ortho and para positions. These results are consistent with experimental data and could be used to propose point mutations that allow this enzyme to process new molecules of biotechnological interest.

Inclusion of ionizing radiation in a mathematical model for photosynthesis.

Ionizing radiation of astrophysical origin might have played an important role in biological evolution during the long course of Earth's evolution. Several phenomena might have induced intense fluctuations in background ionizing radiation, such as highly energetic stellar explosions. There might also be anthropogenic causes for environmental radiation fluctuations, resulting from nuclear industry activities. The inclusion of these effects in a mathematical model for photosynthesis provides a useful tool to account for the damages of the above-mentioned phenomena in vegetal life. Mathematical models for photosynthesis typically only consider ultraviolet radiation and photosynthetically active radiation, as they have been a ubiquitous physical factor in the settlement of vegetal life. In this work a mathematical model for aquatic photosynthesis is modified, from first principles, to include the action of particulate ionizing radiation on the photosynthetic process. After assuming an ansatz allowing to separate damage/repair kinetics of ultraviolet and ionizing radiations, a treatable mathematical expression of the model is obtained. This generalized model is presented as a function of radiometric and photometric magnitudes, making it prone to calibration and useful to apply to aquatic ecosystems under radiational stress due to gamma-ray bursts, cosmic ray bursts, solar storms, or other sources of ionizing radiations.

A new method to map groundwater-dependent ecosystem zones in semi-arid environments: A case study in Chile.

Groundwater (GW) use has intensified in recent decades, threatening the ecological integrity of groundwater-dependent ecosystems (GDEs). The study of GDEs is limited; therefore, integrated, interdisciplinary environmental approaches that guarantee their monitoring and management amid current climate and anthropogenic changes are needed. A new geospatial method with an integrated and temporal approach was developed through a multicriteria approximation, taking into account expert opinion, remote sensing-GIS, and fieldwork to map groundwater-dependent ecosystem zones (GDEZ). A survey of experts (N = 26) was conducted to assign degrees of importance to the various geospatial parameters, and the mapping was carried out using 14 parameters. The reclassified parameters were normalized on a scale of 1 to 5 according to the degree of probability of the presence of GDE. The validation was carried out through fieldwork and statistical analysis. Then, the spatio-temporal changes amid changing GW levels were assessed using the summer season normalized difference vegetation index (NDVI). Two GDEZ maps were obtained, for 2002 and 2017, between which the high- and very-high-probability zones of GDEs decreased by 31,887 ha (~ 38%). The most sensitive temporal parameters that most influenced the spatio-temporal changes on GDEs were precipitation and land use, with rain exerting a slightly the greatest influence. It was also demonstrated that identified ecosystems decreased in area or were affected by aquifer depletion (NDVI-GW, r Pearson ≥0.74). This validated method allows spatio-temporal changes in GDEs to be mapped and analyzed at an annual scale and is transferable to other arid and semi-arid environments.