Inorganic nitrogen concentrations in soil solutions vary across several orders of magnitude among different soils and as a result of seasonal changes. In order to respond to this heterogeneity, plants have evolved mechanisms to regulate and influx. In addition, efflux analysis using (13)N has revealed that there is a co-ordinated regulation of all component fluxes within the root, including biochemical fluxes. Physiological studies have demonstrated the presence of two high-affinity transporter systems (HATS) for and one HATS for in roots of higher plants. By contrast, in Arabidopsis thaliana there exist seven members of the NRT2 family encoding putative HATS for and five members of the AMT1 family encoding putative HATS for. The induction of high-affinity transport and Nrt2.1 and Nrt2.2 expression occur in response to the provision of, while down-regulation of these genes appear to be due to the effects of glutamine. High-affinity transport and AMT1.1 expression also appear to be subject to down-regulation by glutamine. In addition, there is evidence that accumulated and may act post-transcriptionally on transporter function. The present challenge is to resolve the functions of all of these genes. In Aspergillus nidulans and Chlamydomonas reinhardtii there are but two high-affinity transporters and these appear to have undergone kinetic differentiation that permits a greater efficiency of absorption over the wide range of concentration normally found in nature. Such kinetic differentiation may also have occurred among higher plant transporters. The characterization of transporter function in higher plants is currently being inferred from patterns of gene expression in roots and shoots, as well as through studies of heterologous expression systems and knockout mutants.
SummaryThe mechanisms involved in regulating high-af®nity ammonium (NH 4 + ) uptake and the expression of the
Acidobacteria are among the most abundant bacterial phyla found in terrestrial ecosystems, but relatively little is known about their diversity, distribution and most critically, their function. Understanding the functional activities encoded in their genomes will provide insights into their ecological roles. Here we describe the genomes of three novel cold‐adapted strains of subdivision 1 Acidobacteria. The genomes consist of a circular chromosome of 6.2 Mbp for Granulicella mallensis MP5ACTX8, 4.3 Mbp for Granulicella tundricola MP5ACTX9, and 5.0 Mbp for Terriglobus saanensis SP1PR4. In addition, G. tundricola has five mega plasmids for a total genome size of 5.5 Mbp. The three genomes showed an abundance of genes assigned to metabolism and transport of carbohydrates. In comparison to three mesophilic Acidobacteria, namely Acidobacterium capsulatum ATCC 51196, ‘Candidatus Koribacter versatilis’ Ellin345, and ‘Candidatus Solibacter usitatus’ Ellin6076, the genomes of the three tundra soil strains contained an abundance of conserved genes/gene clusters encoding for modules of the carbohydrate‐active enzyme (CAZyme) family. Furthermore, a large number of glycoside hydrolases and glycosyl transferases were prevalent. We infer that gene content and biochemical mechanisms encoded in the genomes of three Arctic tundra soil Acidobacteria strains are shaped to allow for breakdown, utilization, and biosynthesis of diverse structural and storage polysaccharides and resilience to fluctuating temperatures and nutrient‐deficient conditions in Arctic tundra soils.
No abstract
Four aerobic bacteria, designated MP5ACTX2T, MP5ACTX8T, MP5ACTX9T and S6CTX5AT, were isolated from tundra soil of north-western Finland (69° 03′ N 20° 50′ E). Cells of all isolates were Gram-negative, non-motile rods. Phylogenetic analysis indicated that they belonged to the genus Granulicella of subdivision 1 of the phylum Acidobacteria . 16S rRNA gene sequence similarity between the new isolates and the type strains of Granulicella aggregans , Granulicella paludicola , Granulicella pectinivorans and Granulicella rosea ranged from 94 to 99 %. Analysis of the RNA polymerase beta subunit (rpoB) gene sequence indicated that the isolates represented novel species of the genus Granulicella (<92 % rpoB sequence similarity between the isolates and members of the genus Granulicella ). This was also confirmed by low DNA–DNA relatedness (31 %) between strain S6CTX5AT and the type strain of G. pectinivorans , which exhibited 99.1 % 16S rRNA gene sequence similarity and 91.7 % rpoB gene sequence similarity. The isolates grew at pH 3.5–6.5 and at 4–26 °C. Sugars were the preferred growth substrates. The major cellular fatty acids were iso-C15 : 0, C16 : 1ω7c and C16 : 0 and the major isoprenoid quinone was MK-8. The DNA G+C content was 56–60 mol%. On the basis of phylogenetic analysis and chemotaxonomic and physiological data, the isolates represent four novel species of the genus Granulicella , for which the names Granulicella arctica MP5ACTX2T ( = ATCC BAA-1858T = DSM 23128T), Granulicella mallensis MP5ACTX8T ( = ATCC BAA-1857T = DSM 23137T), Granulicella tundricola MP5ACTX9T (ATCC BAA-1859T = DSM 23138T) and Granulicella sapmiensis S6CTX5AT ( = LMG 26174T = DSM 23136T) are proposed. An emended description of the genus Granulicella is also presented.
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