The effects of elevated atmospheric CO(2) (560 p.p.m.) and subsequent plant responses on the soil microbial community composition associated with trembling aspen was assessed through the classification of 6996 complete ribosomal DNA sequences amplified from the Rhinelander WI free-air CO(2) and O(3) enrichment (FACE) experiments microbial community metagenome. This in-depth comparative analysis provides an unprecedented, detailed and deep branching profile of population changes incurred as a response to this environmental perturbation. Total bacterial and eukaryotic abundance does not change; however, an increase in heterotrophic decomposers and ectomycorrhizal fungi is observed. Nitrate reducers of the domain bacteria and archaea, of the phylum Crenarchaea, potentially implicated in ammonium oxidation, significantly decreased with elevated CO(2). These changes in soil biota are evidence for altered interactions between trembling aspen and the microorganisms in its surrounding soil, and support the theory that greater plant detritus production under elevated CO(2) significantly alters soil microbial community composition.

Proteome and transcriptome analysis, combined with mutagenesis, were used to better understand the response of Cupriavidus metallidurans CH34 against lead(II). Structural Pb(II)-resistance genes of the pMOL30-encoded pbrUTRABCD operon formed the major line of defense against Pb(II). However, several general stress response mechanisms under the control of alternative sigma factors such as sigma24/rpoK, sigma32/rpoH and sigma28/fliA were also induced. In addition, the expression of the pbrR(2) cadA pbrC(2) operon of the CMGI-1 region and the chromosomally encoded zntA were clearly induced in the presence of Pb(II), although their respective gene products were not detected via proteomics. After inactivation of the pbrA, pbrB or pbrD genes, the expression of the pbrR(2) cadA pbrC(2) operon went up considerably. This points towards synergistic interactions between pbrUTRABCD and pbrR(2) cadA pbrC(2) to maintain a low intracellular Pb(II) concentration, where pbrR(2) cadA pbrC(2) gene functions can complement and compensate for the mutations in the pbrA and pbrD genes. This role of zntA and cadA to complement for the loss of pbrA was further confirmed by mutation analysis. The pbrB:: colonsTn(Km2) mutation resulted in the most significant decrease of Pb(II) resistance, indicating that Pb(II) sequestration, avoiding re-entry of this toxic metal ion, forms a critical step in the pbr-encoded Pb(II) resistance mechanism.

The transcription factors HNF1B and Pax2, co-expressed in the Wolffian duct and ureteric bud epithelia, play essential roles during the early steps of mouse kidney development. In humans, heterozygous mutations in these genes display a number of common kidney phenotypes, including hypoplasia and multicystic hypoplastic kidneys. Moreover, a high prevalence of mutations either in HNF1B or PAX2 has been observed in children with renal hypodysplasia. To gain a better understanding of Hnf1b and Pax2 interactions in vivo, we generated compound heterozygous mice for Hnf1b and Pax2 null alleles. We show here that compound heterozygous mutants display phenotypes similar to severe congenital anomalies of the kidney and the urinary tract (CAKUT), including strong hypoplasia of the kidneys, caudal ectopic aborted ureter buds, duplex kidneys, megaureters and hydronephrosis. At a molecular level, compound mutants show a delay in nephron segment and medullar interstitial differentiation, increased apoptosis and a transient decrease in Lim1 and Wnt4 expression. We also observe a perturbation of smooth muscle differentiation around the ureter associated with a local down-regulation in transcript levels of Bmp4 and Tbx18, two key regulators involved in ureter smooth muscle formation, thus explaining, at least in part, megaureters. These results together uncover a novel role of Hnf1b as a modifier of the Pax2 haplo-insufficient phenotype and show that these two transcription factors operate in common pathways governing both kidney morphogenesis and ureter differentiation. This mouse model should provide new insights into the pathogenic mechanisms of human CAKUT, the most frequent developmental defect identified in newborns.