Widespread formation of intracellular calcium carbonates by the bloom-forming cyanobacterium Microcystis

The formation of intracellular amorphous calcium carbonates (iACC) has been recently observed in a few cultured strains of Microcystis, a potentially toxic bloom-forming cyanobacterium found worldwide in freshwater ecosystems. If iACC-forming Microcystis are abundant within blooms, they may represent a significant amount of particulate Ca. Here, we investigate the significance of iACC biomineralization by Microcystis. First, the presence of iACC-forming Microcystis cells has been detected in several eutrophic lakes, indicating that this phenomenon occurs under environmental conditions. Second, some genotypic (presence/absence of ccyA, a marker gene of iACC biomineralization) and phenotypic (presence/absence of iACC) diversity have been detected within a collection of strains isolated from one single lake. This illustrates that this trait is frequent but also variable within Microcystis even at a single locality. Finally, one-third of publicly available genomes of Microcystis were shown to contain the ccyA gene, revealing a wide geographic and phylogenetic distribution within the genus. Overall, the present work shows that the formation of iACC by Microcystis is common under environmental conditions. While its biological function remains undetermined, this process should be further considered regarding the biology of Microcystis and implications on the Ca geochemical cycle in freshwater environments.     

Phenotypic effects of overexpression of Agrobacterium rhizogenes T-DNA ORF13 in transgenic tobacco plants are mediated by diffusible factor(s)

Nicotiana tabacum cv. Xanthi transgenic plants expressing ORF13 of Agrobacterium rhizogenes 8196 T-DNA under the 35S RNA promoter from the cauliflower mosaic virus displayed developmental abnormalities. They were small, with short and variable internodal lengths, their root systems were poorly developed; leaves were small, asymmetric, rounded, wrinkled and dark green; flowers were short, and irregularly shaped. They exhibited reduced apical dominance and regularly produced offshoots at the base of the plant. This phenotype was also exhibited by offshoots of normal N. tabacum cv. Xanthi stock grafted with a transgenic scion indicating that expression of ORF13 influences plant development via diffusible factor(s).     

Continuous polyhydroxybutyrate production from biogas in an innovative two-stage bioreactor configuration

Biogas biorefineries have opened up new horizons beyond heat and electricity production in the anaerobic digestion sector. Added-value products such as polyhydroxyalkanoates (PHAs), which are environmentally benign and potential candidates to replace conventional plastics, can be generated from biogas. This work investigated the potential of an innovative two-stage growth-accumulation system for the continuous production of biogas-based polyhydroxybutyrate (PHB) using Methylocystis hirsuta CSC1 as cell factory. The system comprised two turbulent bioreactors in series to enhance methane and oxygen mass transfer: a continuous stirred tank reactor (CSTR) and a bubble column bioreactor (BCB) with internal gas recirculation. The CSTR was devoted to methanotrophic growth under nitrogen balanced growth conditions and the BCB targeted PHB production under nitrogen limiting conditions. Two different operational approaches under different nitrogen loading rates and dilution rates were investigated. A balanced nitrogen loading rate along with a dilution rate (D) of 0.3 day⁻¹ resulted in the most stable operating conditions and a PHB productivity of ~53 g PHB m⁻³ day⁻¹. However, higher PHB productivities (~127 g PHB m⁻³ day⁻¹) were achieved using nitrogen excess at a D = 0.2 day⁻¹. Overall, the high PHB contents (up to 48% w/w) obtained in the CSTR under theoretically nutrient balanced conditions and the poor process stability challenged the hypothetical advantages conferred by multistage vs single-stage process configurations for long-term PHB production.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

Inhibition of ATP-regulated K+-channels by a photoactivatable ATP-analogue in mouse pancreatic β-cells

The effects of a photoactivatable (DMNPE-caged) ATP-analogue on ATP-regulated K⁺-channels (K_ATP-channel) in mouse pancreatic β-cells were investigated using the inside-out patch configuration of the patch-clamp technique. The caged precursor caused a concentration-dependent reduction of channel activity with a K_i of 17 μM; similar to the 11 μM obtained for standard Mg-ATP. The small difference in the blocking capacity between the precursor and ATP is probably the reason why no change in channel activity was observed upon photolysis of the caged molecule and liberation of ATP. It is suggested that the part of the ATP molecule involved in the blocking reaction of the K_ATP-channel is not sufficiently protected in DMNPE-caged ATP making this compound unsuitable for studying the rapid kinetics of ATP-induced K_ATP-channel inhibition.     

EPR and multi-field magnetisation of reduced forms of the binuclear iron centre in ribonucleotide reductase from mouse

Mouse ribonucleotide reductase is composed of a 1?:?1 complex of two homodimeric subunits and catalyses the first unique step on the biochemical pathway to DNA synthesis. The small subunit, protein R2, contains dinuclear iron-oxygen clusters and a tyrosyl free radical required for catalytic activity. We have studied the mixed valent and fully reduced forms of the diiron oxygen cluster from mouse R2 protein by low-temperature EPR. EPR signals of the mixed-valent states of proteins R2 reconstituted with ferrous iron and oxygen in normal and deuterated water, using the same buffers, show apparent g values of 1.92, 1.73, and 1.60 for the mixed-valent state in H₂O and 1.93, 1.73, and 1.62 in D₂O. These g values are typical for diiron-oxygen proteins, while the effect of D₂O is unprecedented for this class of proteins. We estimate the coupling constant J for the Heisenberg exchange (H?=?2J*S₁*S₂) to be J?=?–7.5±1?cm^–1 for the mixed-valent form. The diferrous R2 protein shows an integer spin EPR signal in the presence of azide or 20% glycerol. Variable temperature variable field saturation magnetisation measurements show that only in the azide-complexed R2 protein does a weak ferromagnetic coupling occur (J?=?0.26±0.05?cm^–1), while R2 protein in the absence or presence of 20% glycerol contains non-coupled mononuclear ferrous iron (S?=?2) sites.     

Effect of taurine on wound healing

Summary Taurine which has antioxidant effects is also known to have effects on cell proliferation, inflammation and collagenogenesis. The aim of this study was to investigate the effect of taurine on incisional skin wounds.The mice incised on the dorsal area were divided into control and experimental groups. Saline was injected intraperitoneally to half of the animals in the control group and locally applied to the other half. Fifty mM taurine solution was given intraperitoneally to the first half of the experimental animals and locally to the second half of the experimental group.After four days of treatment, malondialdehyde (MDA) and histamine levels as well as the tensile strength of the wound tissue were measured. Structural alterations in epidermis and dermis were histologically evaluated.The locally administreated taurine significantly increased wound tensile strength by decreasing the MDA and histamine levels and prevented the degranulation of the mast cells. These observations suggest that taurine may be useful on wound healing.     

Precise physical mapping of theEscherichia coli rnb gene, encoding ribonuclease II

Ribonuclease II (encoded byrnb) is one of the two main exonucleases involved in mRNA degradation inEscherichia coli. We report the precise physical mapping ofrnb to 29 min on the chromosomal map in the vicinity ofpyrF, and clarify the genetic and physical maps of thisE. coli chromosomal region. The results were confirmed by the construction of a strain partially deleted forrnb.