Microbial Communities Associated with Zones of Elevated Magnetic Susceptibility in Hydrocarbon-Contaminated Sediments

Recent studies suggest that magnetic susceptibility (MS) measurements can play an important role in identifying zones where microbial-mediated iron mineral transformations are occurring. Here we investigated the microbial community variations within zones of elevated MS in a petroleum hydrocarbon-contaminated aquifer near Bemidji, Minnesota, USA. Our main objective was to 1) identify the key microbial populations that may play a role in hydrocarbon degradation, 2) analyze which microbial populations could be connected to the elevated MS and 3) explore the use of non-destructive geophysical techniques as a tool to guide microbial sampling. Clone libraries based on the 16S rRNA gene revealed the presence of iron-reducing β-Proteobacteria in the vadose zone, whereas the free petroleum phase on the water table was characterized by a methanogenic consortium, in which the syntrophic δ-proteobacterium Smithella and the hydrogenotrophic Methanoregula predominated. Nonmetric multidimensional scaling (NMDS) found a close relationship between elevated MS values and the methanogenic hydrocarbon-degrading consortium. Our results suggest that magnetic susceptibility measurements can guide microbiologists to zones of active microbial biodegradation in aged petroleum spills.     

Generation of a conditional lima1a allele in zebrafish using the FLEx switch technology

Gene trapping has emerged as a valuable tool to create conditional alleles in various model organisms. Here we report the FLEx‐based gene trap vector SAGFLEx that allows the generation of conditional mutations in zebrafish by gene‐trap mutagenesis. The SAGFLEx gene‐trap cassette comprises the rabbit β‐globin splice acceptor and the coding sequence of GFP, flanked by pairs of inversely oriented heterotypic target sites for the site‐specific recombinases Cre and Flp. Insertion of the gene‐trap cassette into endogenous genes can result in conditional mutations that are stably inverted by Cre and Flp, respectively. To test the functionality of this system we performed a pilot screen and analyzed the insertion of the gene‐trap cassette into the lima1a gene locus. In this lima1a allele, GFP expression faithfully recapitulated the endogenous lima1a expression and resulted in a complete knockout of the gene in homozygosity. Application of either Cre or Flp was able to mediate the stable inversion of the gene trap cassette and showed the ability to conditionally rescue or reintroduce the gene inactivation. Combined with pharmacologically inducible site specific recombinases the SAGFLEx vector insertions will enable precise conditional knockout studies in a spatial‐ and temporal‐controlled manner. genesis 54:19–28, 2016. © 2015 Wiley Periodicals, Inc.     

S100A11 plays a role in homologous recombination and genome maintenance by influencing the persistence of RAD51 in DNA repair foci

The repair of DNA double-strand breaks (DSBs) by homologous recombination (HR) is an essential process in maintenance of chromosomal stability. A key player of HR is the strand exchange factor RAD51 whose assembly at sites of DNA damage is tightly regulated. We detected an endogenous complex of RAD51 with the calcium-binding protein S100A11, which is localized at sites of DNA repair in HaCaT cells as well as in normal human epidermal keratinocytes (NHEK) synchronized in S phase. In biochemical assays, we revealed that S100A11 enhanced the RAD51 strand exchange activity. When cells expressing a S100A11 mutant lacking the ability to bind Ca²⁺, a prolonged persistence of RAD51 in repair sites and nuclear γH2AX foci was observed suggesting an incomplete DNA repair. The same phenotype became apparent when S100A11 was depleted by RNA interference. Furthermore, down-regulation of S100A11 resulted in both reduced sister chromatid exchange confirming the restriction of the recombination capacity of the cells, and in an increase of chromosomal aberrations reflecting the functional requirement of S100A11 for the maintenance of genomic stability. Our data indicate that S100A11 is involved in homologous recombination by regulating the appearance of RAD51 in DSB repair sites. This function requires the calcium-binding activity of S100A11.     

Lack of functional P2X7 receptor aggravates brain edema development after middle cerebral artery occlusion

Effective therapeutic measures against the development of brain edema, a life-threatening complication of cerebral ischemia, are necessary to improve the functional outcome for the patient. Here, we identified a beneficial role of purinergic receptor P2X7 activation in acute ischemic stroke. Involvement of P2X7 in the development of neurological deficits, infarct size, brain edema, and glial responses after ischemic cerebral infarction has been analyzed. Neurologic evaluation, magnetic resonance imaging, and immunofluorescence assays were used to characterize the receptor’s effect on the disease progress during 72 h after transient middle cerebral artery occlusion (tMCAO). Sham-operated animals were included in all experiments for control purposes. We found P2X7-deficient mice to develop a more prominent brain edema with a trend towards more severe neurological deficits 24 h after tMCAO. Infarct sizes, T2 times, and apparent diffusion coefficients did not differ significantly between wild-type and P2X7^?/? animals. Our results show a characteristic spatial distribution of reactive glia cells with strongly attenuated microglia activation in P2X7^?/? mice 72 h after tMCAO. Our data indicate that P2X7 exerts a role in limiting the early edema formation, possibly by modulating glial responses, and supports later microglia activation.     

Multiple chromosomal rearrangements in a hybrid zone between Littorina saxatilis ecotypes

Both classical and recent studies suggest that chromosomal inversion polymorphisms are important in adaptation and speciation. However, biases in discovery and reporting of inversions make it difficult to assess their prevalence and biological importance. Here, we use an approach based on linkage disequilibrium among markers genotyped for samples collected across a transect between contrasting habitats to detect chromosomal rearrangements de novo. We report 17 polymorphic rearrangements in a single locality for the coastal marine snail, Littorina saxatilis. Patterns of diversity in the field and of recombination in controlled crosses provide strong evidence that at least the majority of these rearrangements are inversions. Most show clinal changes in frequency between habitats, suggestive of divergent selection, but only one appears to be fixed for different arrangements in the two habitats. Consistent with widespread evidence for balancing selection on inversion polymorphisms, we argue that a combination of heterosis and divergent selection can explain the observed patterns and should be considered in other systems spanning environmental gradients.