Isolation and nucleotide sequence of the GDP-mannose:cellobiosyl- diphosphopolyprenol α-mannosyltransferase gene from Acetobacter xylinum

A genetic locus from Acetobacter xylinum involved in acetan polysaccharide synthesis has been characterized. The chromosomal region was identified by screening a genomic library of A. xylinum in a Xanthomonas campestris mutant defective in xanthan polysaccharide synthesis. The A. xylinum cosmid clone can functionally complement a xanthan-negative mutant. The polymer produced by the recombinant strain was found to be indistinguishable from xanthan. Insertion mutagenesis and subcloning of the cosmid clone combined with complementation studies allowed the identification of a 2.3-kb fragment of A. xylinum chromosomal DNA. The nucleotide sequence of this fragment was analyzed and found to contain an open reading frame (aceA) of 1,182 bp encoding a protein of 43.2 kDa. Results from biochemical and genetic analyses strongly suggest that the aceA gene encodes the GDP- mannose:cellobiosyl-diphosphopolyprenol α-mannosyltransferase enzyme, which is responsible for the transfer of an α-mannosyl residue from GDP-Man to cellobiosyl-diphosphopolyprenol. A search for similarities with other known mannosyltransferases revealed that all bacterial α-mannosyltransferases have a short COOH-termina1 amino acid sequence in common.Fil:Petroni, E.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ielpi, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

A novel galacturonide from Xanthomonas campestris

Enzyme preparations from Xanthomonas campestris incubated in the presence of UDP-[14C]GlcA and Mg2+ produced a lipophilic galacturonide with unusual properties. It was easily degraded by both mild acid treatment (0.01 M-HCl, 100°C, 10 min) and mild alkali treatment (0.06 M-NaOH, room temperature, 5 min) releasing free [14C]galacturonic acid. The galacturonide appeared to be a single compound with one negative charge, as judged by TLC, paper electrophoresis and chromotography, LH-20 gel filtration and DEAE-cellulose column chromatography. Competition experiments indicated that the true glycosyl donor was UDP-GalA, in agreement with the detection of UDP-GlcA-4-epimerase activity in the crude enzyme preparation. The transglycosidase activity was located mainly in the membrane fraction. UDP inhibited the reaction and even produced some loss of label, suggesting an easily reversible reaction. UMP had almost no effect.Fil:Baldessari, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ielpi, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Dankert, M.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Meandering rivers in modern desert basins: Implications for channel planform controls and prevegetation rivers

The influence of biotic processes in controlling the development of meandering channels in fluvial systems is controversial. The majority of the depositional history of the Earth's continents was devoid of significant biogeomorphic interactions, particularly those between vegetation and sedimentation processes. The prevailing perspective has been that prevegetation meandering channels rarely developed and that rivers with braided planforms dominated. However, recently acquired data demonstrate that meandering channel planforms are more widely preserved in prevegetation fluvial successions than previously thought. Understanding the role of prevailing fluvial dynamics in non- and poorly vegetated environments must rely on actualistic models derived from presently active rivers developed in sedimentary basins subject to desert-climate settings, the sparsest vegetated regions experiencing active sedimentation on Earth. These systems have fluvial depositional settings that most closely resemble those present in prevegetation (and extra-terrestrial) environments. Here, we present an analysis based on satellite imagery which reveals that rivers with meandering channel planforms are common in modern sedimentary basins in desert settings. Morphometric analysis of meandering fluvial channel behaviour, where vegetation is absent or highly restricted, shows that modern sparsely and non-vegetated meandering rivers occur across a range of slope gradients and basin settings, and possess a broad range of channel and meander-belt dimensions. The importance of meandering rivers in modern desert settings suggests that their abundance is likely underestimated in the prevegetation rock record, and models for recognition of their deposits need to be improved

Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields

Complete Genome Sequence of the N2-Fixing Broad Host Range Endophyte Klebsiella pneumoniae 342 and Virulence Predictions Verified in Mice

We report here the sequencing and analysis of the genome of the nitrogen-fixing endophyte, Klebsiella pneumoniae 342. Although K. pneumoniae 342 is a member of the enteric bacteria, it serves as a model for studies of endophytic, plant-bacterial associations due to its efficient colonization of plant tissues (including maize and wheat, two of the most important crops in the world), while maintaining a mutualistic relationship that encompasses supplying organic nitrogen to the host plant. Genomic analysis examined K. pneumoniae 342 for the presence of previously identified genes from other bacteria involved in colonization of, or growth in, plants. From this set, approximately one-third were identified in K. pneumoniae 342, suggesting additional factors most likely contribute to its endophytic lifestyle. Comparative genome analyses were used to provide new insights into this question. Results included the identification of metabolic pathways and other features devoted to processing plant-derived cellulosic and aromatic compounds, and a robust complement of transport genes (15.4%), one of the highest percentages in bacterial genomes sequenced. Although virulence and antibiotic resistance genes were predicted, experiments conducted using mouse models showed pathogenicity to be attenuated in this strain. Comparative genomic analyses with the presumed human pathogen K. pneumoniae MGH78578 revealed that MGH78578 apparently cannot fix nitrogen, and the distribution of genes essential to surface attachment, secretion, transport, and regulation and signaling varied between each genome, which may indicate critical divergences between the strains that influence their preferred host ranges and lifestyles (endophytic plant associations for K. pneumoniae 342 and presumably human pathogenesis for MGH78578). Little genome information is available concerning endophytic bacteria. The K. pneumoniae 342 genome will drive new research into this less-understood, but important category of bacterial-plant host relationships, which could ultimately enhance growth and nutrition of important agricultural crops and development of plant-derived products and biofuels

Isolation and nucleotide sequence of the GDP-mannose:cellobiosyl- diphosphopolyprenol α-mannosyltransferase gene from Acetobacter xylinum

A genetic locus from Acetobacter xylinum involved in acetan polysaccharide synthesis has been characterized. The chromosomal region was identified by screening a genomic library of A. xylinum in a Xanthomonas campestris mutant defective in xanthan polysaccharide synthesis. The A. xylinum cosmid clone can functionally complement a xanthan-negative mutant. The polymer produced by the recombinant strain was found to be indistinguishable from xanthan. Insertion mutagenesis and subcloning of the cosmid clone combined with complementation studies allowed the identification of a 2.3-kb fragment of A. xylinum chromosomal DNA. The nucleotide sequence of this fragment was analyzed and found to contain an open reading frame (aceA) of 1,182 bp encoding a protein of 43.2 kDa. Results from biochemical and genetic analyses strongly suggest that the aceA gene encodes the GDP- mannose:cellobiosyl-diphosphopolyprenol α-mannosyltransferase enzyme, which is responsible for the transfer of an α-mannosyl residue from GDP-Man to cellobiosyl-diphosphopolyprenol. A search for similarities with other known mannosyltransferases revealed that all bacterial α-mannosyltransferases have a short COOH-termina1 amino acid sequence in common.Fil:Petroni, E.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ielpi, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Isolation and nucleotide sequence of the GDP-mannose:cellobiosyl-diphosphopolyprenol alpha-mannosyltransferase gene from Acetobacter xylinum.

A genetic locus from Acetobacter xylinum involved in acetan polysaccharide synthesis has been characterized. The chromosomal region was identified by screening a genomic library of A. xylinum in a Xanthomonas campestris mutant defective in xanthan polysaccharide synthesis. The A. xylinum cosmid clone can functionally complement a xanthan-negative mutant. The polymer produced by the recombinant strain was found to be indistinguishable from xanthan. Insertion mutagenesis and subcloning of the cosmid clone combined with complementation studies allowed the identification of a 2.3-kb fragment of A. xylinum chromosomal DNA. The nucleotide sequence of this fragment was analyzed and found to contain an open reading frame (aceA) of 1,182 bp encoding a protein of 43.2 kDa. Results from biochemical and genetic analyses strongly suggest that the aceA gene encodes the GDP-mannose:cellobiosyl-diphosphopolyprenol alpha-mannosyltransferase enzyme, which is responsible for the transfer of an alpha-mannosyl residue from GDP-Man to cellobiosyl-diphosphopolyprenol. A search for similarities with other known mannosyltransferases revealed that all bacterial alpha-mannosyltransferases have a short COOH-terminal amino acid sequence in common

Lipid-linked intermediates in the biosynthesis of xanthan gum

Fil:Ielpi, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Couso, R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Dankert, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

A novel galacturonide from Xanthomonas campestris

Enzyme preparations from Xanthomonas campestris incubated in the presence of UDP-&#91;14C&#93;GlcA and Mg2+ produced a lipophilic galacturonide with unusual properties. It was easily degraded by both mild acid treatment (0.01 M-HCl, 100°C, 10 min) and mild alkali treatment (0.06 M-NaOH, room temperature, 5 min) releasing free &#91;14C&#93;galacturonic acid. The galacturonide appeared to be a single compound with one negative charge, as judged by TLC, paper electrophoresis and chromotography, LH-20 gel filtration and DEAE-cellulose column chromatography. Competition experiments indicated that the true glycosyl donor was UDP-GalA, in agreement with the detection of UDP-GlcA-4-epimerase activity in the crude enzyme preparation. The transglycosidase activity was located mainly in the membrane fraction. UDP inhibited the reaction and even produced some loss of label, suggesting an easily reversible reaction. UMP had almost no effect.Fil:Baldessari, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ielpi, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Dankert, M.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina