It's all about the children: a participant-driven photo-elicitation study of Mexican-origin mothers' food choices

Abstract Background There is a desperate need to address diet-related chronic diseases in Mexican-origin women, particularly for those in border region colonias (Mexican settlements) and other new destination communities in rural and non-rural areas of the U.S. Understanding the food choices of mothers, who lead food and health activities in their families, provides one way to improve health outcomes in Mexican-origin women and their children. This study used a visual method, participant-driven photo-elicitation, and grounded theory in a contextual study of food choices from the perspectives of Mexican-origin mothers. Methods Teams of trained promotoras (female community health workers from the area) collected all data in Spanish. Ten Mexican-origin mothers living in colonias in Hidalgo County, TX completed a creative photography assignment and an in-depth interview using their photographs as visual prompts and examples. English transcripts were coded inductively by hand, and initial observations emphasized the salience of mothers' food practices in their routine care-giving. This was explored further by coding transcripts in the qualitative data analysis software Atlas.ti. Results An inductive conceptual framework was created to provide context for understanding mothers' daily practices and their food practices in particular. Three themes emerged from the data: 1) a mother's primary orientation was toward her children; 2) leveraging resources to provide the best for her children; and 3) a mother's daily food practices kept her children happy, healthy, and well-fed. Results offer insight into the intricate meanings embedded in Mexican-origin mothers' routine food choices. Conclusions This paper provides a new perspective for understanding food choice through the eyes of mothers living in the colonias of South Texas -- one that emphasizes the importance of children in their routine food practices and the resilience of the mothers themselves. Additional research is needed to better understand mothers' perspectives and food practices with larger samples of women and among other socioeconomic groups

Cyanobacterial nitrogenases: phylogenetic diversity, regulation and functional predictions

Abstract Cyanobacteria is a remarkable group of prokaryotic photosynthetic microorganisms, with several genera capable of fixing atmospheric nitrogen (N2) and presenting a wide range of morphologies. Although the nitrogenase complex is not present in all cyanobacterial taxa, it is spread across several cyanobacterial strains. The nitrogenase complex has also a high theoretical potential for biofuel production, since H2 is a by-product produced during N2 fixation. In this review we discuss the significance of a relatively wide variety of cell morphologies and metabolic strategies that allow spatial and temporal separation of N2 fixation from photosynthesis in cyanobacteria. Phylogenetic reconstructions based on 16S rRNA and nifD gene sequences shed light on the evolutionary history of the two genes. Our results demonstrated that (i) sequences of genes involved in nitrogen fixation (nifD) from several morphologically distinct strains of cyanobacteria are grouped in similarity with their morphology classification and phylogeny, and (ii) nifD genes from heterocytous strains share a common ancestor. By using this data we also discuss the evolutionary importance of processes such as horizontal gene transfer and genetic duplication for nitrogenase evolution and diversification. Finally, we discuss the importance of H2 synthesis in cyanobacteria, as well as strategies and challenges to improve cyanobacterial H2 production

Uncoupling nitrogenase: catalytic reduction of hydrazine to ammonia by a MoFe protein in the absence of Fe protein-ATP.

The catalytic reduction of hydrazine (N(2)H(4)) to ammonia by a β-98(Tyr→His) MoFe protein in the absence of the Fe protein or ATP is reported. The reduction of N(2) or other substrates (e.g., hydrazine, protons, acetylene) by nitrogenase normally requires the transient association of the two nitrogenase component proteins, the Fe protein and the MoFe protein. The Fe protein, with two bound MgATP molecules, transfers one electron to the MoFe protein during each association, coupled to the hydrolysis of two MgATP. All substrate reduction reactions catalyzed by nitrogenase require delivery of electrons by the Fe protein coupled to the hydrolysis of MgATP. We report that when a single amino acid within the MoFe protein (β-98(Tyr)) is substituted by His, the resulting MoFe protein supports catalytic reduction of the nitrogenous substrate hydrazine (N(2)H(4)) to two ammonia molecules when provided with a low potential reductant, polyaminocarboxylate ligated Eu(II) (E(m) -1.1 V vs NHE). The wild-type and a number of other MoFe proteins with amino acid substitutions do not show significant rates of hydrazine reduction under these conditions, whereas the β-98(His) MoFe protein catalyzes hydrazine reduction at rates up to 170 nmol NH(3)/min/mg MoFe protein. This rate of hydrazine reduction is 94% of the rate catalyzed by the β-98(His) or wild-type MoFe protein when combined with the Fe protein, ATP, and reductant under comparable conditions. The β-98(His) MoFe protein reduction of hydrazine in the absence of the Fe protein showed saturation kinetics for the concentration of reductant and substrate. The implications of these results in understanding the nitrogenase mechanism are discussed

Specificity of NifEN and VnfEN for the Assembly of Nitrogenase Active Site Cofactors in Azotobacter vinelandii

Deutsche Forschungsgemeinschaft RTG1976The nitrogen-fixing microbe Azotobacter vinelandii has the ability to produce three genetically distinct, but mechanistically similar, components that catalyze nitrogen fixation. For two of these components, the Mo-dependent and V-dependent components, their corresponding metal-containing active site cofactors, designated FeMo-cofactor and FeV-cofactor, respectively, are preformed on separate molecular scaffolds designated NifEN and VnfEN, respectively. From prior studies, and the present work, it is now established that neither of these scaffolds can replace the other with respect to their in vivo cofactor assembly functions. Namely, a strain inactivated for NifEN cannot produce active Mo-dependent nitrogenase nor can a strain inactivated for VnfEN produce an active V-dependent nitrogenase. It is therefore proposed that metal specificities for FeMo-cofactor and FeV-cofactor formation are supplied by their respective assembly scaffolds. In the case of the third, Fe-only component, its associated active site cofactor, designated FeFe-cofactor, requires neither the NifEN nor VnfEN assembly scaffold for its formation. Furthermore, there are no other genes present in A. vinelandii that encode proteins having primary structure similarity to either NifEN or VnfEN. It is therefore concluded that FeFe-cofactor assembly is completed within its cognate catalytic protein partner without the aid of an intermediate assembly site. IMPORTANCE Biological nitrogen fixation is a complex process involving the nitrogenases. The biosynthesis of an active nitrogenase involves a large number of genes and the coordinated function of their products. Understanding the details of the assembly and activation of the different nitrogen fixation components, in particular the simplest one known so far, the Fe-only nitrogenase, would contribute to the goal of transferring the necessary genetic elements of bacterial nitrogen fixation to cereal crops to endow them with the capacity for self-fertilization. In this work, we show that there is no need for a scaffold complex for the assembly of the FeFe-cofactor, which provides the active site for Fe-only nitrogenase. These results are in agreement with previously reported genetic reconstruction experiments using a non-nitrogen-fixing microbe. In aggregate, these findings provide a high degree of confidence that the Fe-only system represents the simplest and, therefore, most attractive target for mobilizing nitrogen fixation into plants.Work performed in the laboratory of D.R.D. was supported by Bill and Melinda Gates Foundation grants BNF Cereals Phase II (OPP1143172) and BNF Cereals phase III (INV-005889), work performed in the laboratory of O.E. was supported by funds from Deutsche Forschungsgemeinschaft grant RTG1976, and work performed in the laboratory of L.C.S. was supported by a grant from the U.S. Department of Energy, Office of Science, (BES) DE-SC0010687.Peer reviewe

Infrared spectroscopy of the nitrogenase MoFe protein under electrochemical control: potential-triggered CO binding.

We demonstrate electrochemical control of the nitrogenase MoFe protein, in the absence of Fe protein or ATP, using europium(iii/ii) polyaminocarboxylate complexes as electron transfer mediators. This allows the potential dependence of proton reduction and inhibitor (CO) binding to the active site FeMo-cofactor to be established. Reduction of protons to H2 is catalyzed by the wild type MoFe protein and β-98Tyr→His and β-99Phe→His variants of the MoFe protein at potentials more negative than -800 mV (vs. SHE), with greater electrocatalytic proton reduction rates observed for the variants compared to the wild type protein. Electrocatalytic proton reduction is strongly attenuated by carbon monoxide (CO), and the potential-dependence of CO binding to the FeMo-cofactor is determined by in situ infrared (IR) spectroelectrochemistry. The vibrational wavenumbers for CO coordinated to the FeMo-cofactor are consistent with earlier IR studies on the MoFe protein with Fe protein/ATP as reductant showing that electrochemically generated states of the protein are closely related to states generated with the native Fe protein as electron donor