The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances

Due to a growing world population and increasing welfare, energy demand worldwide is increasing. To meet the increasing energy demand in a sustainable way, new technologies are needed. The Plant-Microbial Fuel Cell (P-MFC) is a technology that could produce sustainable bio-electricity and help meeting the increasing energy demand. Power output of the P-MFC, however, needs to be increased to make it attractive as a renewable and sustainable energy source. To increase power output of the P-MFC internal resistances need to be reduced. With a flat-plate P-MFC design we tried to minimize internal resistances compared to the previously used tubular P-MFC design. With the flat-plate design current and power density per geometric planting area were increased (from 0.15 A/m² to 1.6 A/m² and from 0.22 W/m² to and 0.44 W/m²)as were current and power output per volume (from 7.5 A/m³ to 122 A/m³ and from 1.3 W/m³ to 5.8 W/m³). Internal resistances times volume were decreased, even though internal resistances times membrane surface area were not. Since the membrane in the flat-plate design is placed vertically, membrane surface area per geometric planting area is increased, which allows for lower internal resistances times volume while not decreasing internal resistances times membrane surface area. Anode was split into three different sections on different depths of the system, allowing to calculate internal resistances on different depths. Most electricity was produced where internal resistances were lowest and where most roots were present; in the top section of the system. By measuring electricity production on different depths in the system, electricity production could be linked to root growth. This link offers opportunities for material-reduction in new designs. Concurrent reduction in material use and increase in power output brings the P-MFC a step closer to usable energy density and economic feasibility.     

Zisupton--a novel superfamily of DNA transposable elements recently active in fish

Transposable elements are widespread mobile DNA sequences able to integrate into new locations within genomes. Through transposition and recombination, they significantly contribute to genome plasticity and evolution. They can also regulate gene expression and provide regulatory and coding sequences (CDSs) for the evolution of novel gene functions. We have identified a new superfamily of DNA transposon on the Y chromosome of the platyfish Xiphophorus maculatus. This element is 11 kb in length and carries a single CDS of 24 exons. The N-terminal part of the putative protein, which is expressed in all adult tissues tested, contains several nucleic acid- and protein-binding domains and might correspond to a novel type of transposase/integrase not described so far in any transposon. In addition, a testis-specific splice isoform encodes a C-terminal Ulp1 SUMO protease domain, suggesting a function in posttranslational protein modification mediated by SUMO and/or ubiquitin small peptides. Accordingly, this element was called Zisupton, for Zinc finger SUMO protease transposon. Beside the Y-chromosomal sequence, five other very similar copies were identified in the platyfish genome. All copies are delimited by 99-bp conserved subterminal inverted repeats and flanked by copy-specific 8-nt target site duplications reflecting their integration at different positions in the genome. Zisupton elements are inserted at different genomic locations in different poeciliid species but also in different populations of X. maculatus. Such insertion polymorphisms between related species and populations indicate relatively recent transposition activity, with a high degree of nucleotide identity between species suggesting possible implication of horizontal gene transfer. Zisupton sequences were detected in other fish species, in urochordates, cephalochordates, and hemichordates as well as in more distant organisms, such as basidiomycete fungi, filamentous brown algae, and green algae. Possible examples of nuclear genes derived from Zisupton have been identified. To conclude, our analysis has uncovered a new superfamily of DNA transposons with potential roles in genome diversity and evolutionary innovation in fish and other organisms.     

Pigmentary function and evolution of tyrp1 gene duplicates in fish

The function of the tyrosinase‐related protein 1 (Tyrp1) has not yet been investigated in vertebrates basal to tetrapods. Teleost fishes have two duplicates of the tyrp1 gene. Here, we show that the teleost tyrp1 duplicates have distributed the ancestral gene expression in the retinal pigment epithelium (RPE) and melanophores in a species‐specific manner. In medaka embryos, tyrp1a expression is found in the RPE and in melanophores while tyrp1b is only expressed in melanophores. In zebrafish embryos, expression of tyrp1 paralogs overlaps in the RPE and in melanophores. Knockdown of each zebrafish tyrp1 duplicate alone does not show pigmentary defects, but simultaneous knockdown of both tyrp1 genes results in the formation of brown instead of black eumelanin accompanied by severe melanosome defects. Our study suggests that the brown melanosome color in Tyrp1‐deficient vertebrates is an effect of altered eumelanin synthesis. Black eumelanin formation essentially relies on the presence of Tyrp1 and some of its function is most likely conserved from the common ancestor of bony vertebrates.     

Modern evolution of a single-copy gene: the immunoglobulin C kappa locus in wild mice

The immunoglobulin kappa light-chain constant region gene (C kappa) has been cloned and sequenced from five wild mouse species. Analysis of these data has permitted an assessment of single-copy gene evolution during a limited time period as defined by the genus Mus. Sequence conservation was found to be as high (or higher) in the 5' and enhancer regions as in the coding region. The pattern of substitutions throughout these genes suggests that parallel evolution has occurred frequently and that substitutions at replacement sites have not decreased significantly, owing to saturation during this period of approximately 10 Myr. Phylogenetic relationships have been determined among these wild species as well as among members of the genus Rattus.      

Artificial circularization of the chromosome with concomitant deletion of its terminal inverted repeats enhances genetic instability and genome rearrangement in Streptomyces lividans

The unstable linear chromosome of Streptomyces lividans was circularized by homologous recombination and its terminal inverted repeats deleted. Strains with circularized chromosomes showed no obvious phenotypic disadvantages compared to the wild type. However, they segregated about 20 times more chloramphenicol-sensitive mutants than the wild type (24.3% vs. 1.4%), due to a higher incidence of large deletions. In addition, in all circularized chromosomes amplification of 30–60 kb fragments was observed at the new chromosomal junction, to levels of approximately 10 copies per chromosome. Arginine auxotrophs that arose spontaneously among the progeny of strains with a circularized chromosome showed high-copy-number amplification of the DNA element AUD1, as also seen in mutants of the wild type. These observations demonstrate that the circular form of the Streptomyces chromosome is more unstable than the linear one. Received: 28 July 1996 / Accepted: 18 November 1996