Human health risks of metalloids and metals in muscle tissue of silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) from Lake Flag Boshielo,South Africa

The Olifants River, a major tributary of the Limpopo River, is one of the most polluted rivers in South Africa. Consequently, concerns regarding the human health impact of long-term consumption of fish from the Olifants River have been raised in recent studies. Nevertheless, Lake Flag Boshielo situated on the main stem of the Olifants River has been proposed as a site for an inland fishery. Planktivorous silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) is among the potential target species for such a fishery. Therefore, a desk-top human health risk assessment was conducted for silver carp from Lake Flag Boshielo. From January to November 2013, muscle samples from 50 specimens were collected and analysed for metals and metalloids. The hazard quotient based on a weekly meal of 150 g exceeded the acceptable level for As, Cd, Cr, Co, Pb, Hg, Se, V and Zn. Compared with previous studies from Lake Flag Boshielo, muscle tissue concentrations of As, Cr, Pb, Hg, Se, V and Zn for H. molitrix were higher. Based on the metal and metalloid concentrations reported in this study, long-term consumption of silver carp from Lake Flag Boshielo might pose a health risk to impoverished rural communities.     

Extraction of food consumption systems by nonnegative matrix factorization (NMF) for the assessment of food choices

In Western countries where food supply is satisfactory, consumers organize their diets around a large combination of foods. It is the purpose of this article to examine how recent nonnegative matrix factorization (NMF) techniques can be applied to food consumption data to understand these combinations. Such data are nonnegative by nature and of high dimension. The NMF model provides a representation of consumption data through latent vectors with nonnegative coefficients, that we call consumption systems (CS), in a small number. As the NMF approach may encourage sparsity of the data representation produced, the resulting CS are easily interpretable. Beyond the illustration of its properties we provide through a simple simulation result, the NMF method is applied to data issued from a French consumption survey. The numerical results thus obtained are displayed and thoroughly discussed. A clustering based on the k-means method is also achieved in the resulting latent consumption space, to recover food consumption patterns easily usable for nutritionists.     

Microwave-induced facile synthesis of water-soluble fluorogenic alginic acid derivatives

A facile microwave-induced method was developed for synthesizing water-soluble fluorescent derivatives of alginic acid (ALG) with four different diamines, hydrazine (HY), ethylenediamine (EDA), 1,6-hexanediamine (HDA), and 1,4-cyclohexanediamine (CHDA), followed by a cross-linking reaction with a natural cross linker genipin. The ethylenediamine derivative of alginic acid (ALG-EDA) exhibited good fluorescent activity, which upon cross linking was enhanced threefold. The other amide derivatives, for example, ALG-HY, ALG-HDA, and ALG-CHDA, were not fluorescent, but their respective crosslinked products exhibited excellent fluorescent activity. The fluorescence intensity had an inverse correlation with the number of carbon atoms present in the amine, which in turn was a function of degree of substitution (DS). These fluorescent polysaccharide derivatives are of potential utility in the domain of sensor applications.     

An alternative structural isoform in amyloid‐like aggregates formed from thermally denatured human γD‐crystallin

The eye lens protein γD‐crystallin contributes to cataract formation in the lens. In vitro experiments show that γD‐crystallin has a high propensity to form amyloid fibers when denatured, and that denaturation by acid or UV‐B photodamage results in its C‐terminal domain forming the β‐sheet core of amyloid fibers. Here, we show that thermal denaturation results in sheet‐like aggregates that contain cross‐linked oligomers of the protein, according to transmission electron microscopy and SDS‐PAGE. We use two‐dimensional infrared spectroscopy to show that these aggregates have an amyloid‐like secondary structure with extended β‐sheets, and use isotope dilution experiments to show that each protein contributes approximately one β‐strand to each β‐sheet in the aggregates. Using segmental ¹³C labeling, we show that the organization of the protein's two domains in thermally induced aggregates results in a previously unobserved structure in which both the N‐terminal and C‐terminal domains contribute to β‐sheets. We propose a model for the structural organization of the aggregates and attribute the recruitment of the N‐terminal domain into the fiber structure to intermolecular cross linking.     

Structural diversity of bacterial flagellar motors

The bacterial flagellum is one of nature's most amazing and well-studied nanomachines. Its cell-wall-anchored motor uses chemical energy to rotate a microns-long filament and propel the bacterium towards nutrients and away from toxins. While much is known about flagellar motors from certain model organisms, their diversity across the bacterial kingdom is less well characterized, allowing the occasional misrepresentation of the motor as an invariant, ideal machine. Here, we present an electron cryotomographical survey of flagellar motor architectures throughout the Bacteria. While a conserved structural core was observed in all 11 bacteria imaged, surprisingly novel and divergent structures as well as different symmetries were observed surrounding the core. Correlating the motor structures with the presence and absence of particular motor genes in each organism suggested the locations of five proteins involved in the export apparatus including FliI, whose position below the C-ring was confirmed by imaging a deletion strain. The combination of conserved and specially-adapted structures seen here sheds light on how this complex protein nanomachine has evolved to meet the needs of different species.