Papers by Author: Verónica Martínez

Abstract: Previous physiological studies of the genus Ferroplasma have indicated that these microorganisms are capable of fixing CO2 in the presence of ferrous iron and low concentrations of yeast extract. Analysis of the gene complement of Ferroplasma acidarmanus fer1 and two partial genomes of Ferroplasma type I and II derived from the Iron Mountain acid mine drainage metagenome revealed the absence of several functional marker genes encoding key enzymes of three know alternative CO2 fixation routes present in archaea, i.e. the 3-hydroxypropionate cycle, the Ljungdahl–Wood pathway and the reverse TCA cycle. It is thus intriguing how these chemoautotrophic archaeal species deal with their requirements for carbon and suggests that they might have a distinct CO2 fixation route, as yet unreported. Using comparative genomics and metabolic reconstruction strategies, a putative pathway was detected for C1 fixation consisting of four main steps: 1) conversion of carbon monoxide to carbon dioxide with gain of energy and/or 2) reduction of carbon dioxide to formate, 3) incorporation of formate to tetrahydrofolate and 4) donation of the carbon moiety of tetrahydrofolate to glycine to produce serine. Steps 1 to 3 involve enzymes that correspond to some of the Ljungdahl–Wood pathway proteins, whereas step 4 resembles the well known “serine cycle”, utilized by methylotrophic microorganisms for formaldehyde fixation. Thus, this chimaeric pathway might represent the missing carbon fixation route in Ferroplasmatales. Herein, we discuss the implications of these findings in the context of central carbon metabolism requirements for biomass production in acidic environments.

Abstract: An understanding of the physiology and metabolic complexity of microbial consortia involved in metal solubilization is a prerequisite for the rational improvement of bioleaching technologies. Among the most challenging aspects that remain to be addressed is how aerobic acidophiles, especially Fe(II)-oxidizers, contend with the paradoxical hazards of iron overload and iron deficiency, each with deleterious consequences for growth. Homeostatic mechanisms regulating the acquisition, utilization/oxidation, storage and intracellular mobilization of cellular iron are deemed to be critical for fitness and survival of bioleaching microbes. In an attempt to contribute to the comprehensive understanding of the biology and ecology of the microbial communities in bioleaching econiches, we have used comparative genomics and other bioinformatic tools to reconstruct the iron management strategies in newly sequenced acidithiobacilli and other biomining genomes available in public databases. Species-specific genes have been identified with distinctive functional roles in iron management as well as genes shared by several species in biomining consortia. Their analysis contributes to our understanding of the general survival strategies in acidic and iron loaded environments and suggests functions for genes with currently unknown functions that might reveal novel aspects of iron response in acidophiles. Comprehensive examination of the occurrence and conservation of regulatory functions and regulatory sites also allowed the prediction of the metal regulatory networks for these biomining microbes.

Abstract: Ceramic materials exhibit very low fracture toughness, which limits their applications. Recently, metal-ceramic composites have been developed to achieve improvements in toughness. In this work, the fracture toughness of SiC-Cu based alloys cermets, obtained by reactive infiltration, was measured at room temperature using the single edge notched beam (SENB) method. Values up to 11 MPam1/2 were obtained; these values were compared with the fracture toughness of commercial materials. The results of fracture toughness were directly related with the amount of the infiltrated metallic phase. The fracture energy was calculated using values of KIC and Young Modulus obtained from four points bending tests. Differences on toughness values were related with porosity and type of fracture of the several systems. The microstructural analysis of the fracture surfaces was carried out by scanning electron microscopy. The role of different operating toughening mechanisms; such as crack deflection, bridging, branching, and energy dissipation through microcracking and/or microplasticity; has been examined.