Topic
Azoarcus
About: Azoarcus is a research topic. Over the lifetime, 216 publications have been published within this topic receiving 13149 citations.
Papers published on a yearly basis
Papers
TL;DR: Four aspects of the Azospirillum-plant root interaction are highlighted: natural habitat, plant root interaction, nitrogen fixation and biosynthesis of plant growth hormones, and the relevance of each of these four aspects for plant growth promotion by AzospIRillum is discussed.
Abstract: Azospirillum represents the best characterized genus of plant growth-promoting rhizobacteria. Other free-living diazotrophs repeatedly detected in association with plant roots, include Acetobacter diazotrophicus, Herbaspirillum seropedicae, Azoarcus spp. and Azotobacter. Four aspects of the Azospirillum–plant root interaction are highlighted: natural habitat, plant root interaction, nitrogen fixation and biosynthesis of plant growth hormones. Each of these aspects is dealt with in a comparative way. Azospirilla are predominantly surface-colonizing bacteria, whereas A. diazotrophicus, H. seropedicae and Azoarcus sp. are endophytic diazotrophs. The attachment of Azospirillum cells to plant roots occurs in two steps. The polar flagellum, of which the flagellin was shown to be a glycoprotein, mediates the adsorption step. An as yet unidentified surface polysaccharide is believed to be essential in the subsequent anchoring phase. In Azoarcus sp. the attachment process is mediated by type IV pili. Nitrogen fixation structural genes (nif) are highly conserved among all nitrogen-fixing bacteria, and in all diazotrophic species of the class of proteobacteria examined, the transcriptional activator NifA is required for expression of other nif genes in response to two major environmental signals (oxygen and fixed N). However, the mechanisms involved in this control can vary in different organisms. In Azospirillum brasilense and H. seropedicae (α- and β-subgroup, respectively), NifA is inactive in conditions of excess nitrogen. Activation of NifA upon removal of fixed N seems to involve, either directly or indirectly, the signal transduction protein PII. The presence of four conserved cysteine residues in the NifA protein might be an indication that NifA is directly sensitive to oxygen. In Azotobacter vinelandii (γ-subgroup) nifA is cotranscribed with a second gene nifL. The nifL gene product inactivates NifA in response to high oxygen tension and cellular nitrogen-status. NifL was found to be a redox-sensitive flavoprotein. The relief of NifL inhibition on NifA activity, in response to N-limitation, is suggested to involve a PII-like protein. Moreover, nitrogenase activity is regulated according to the intracellular nitrogen and O2 level. In A. brasilense and Azospirillum lipoferum posttranslational control of nitrogenase, in response to ammonium and anaerobiosis, involves ADP-ribosylation of the nitrogenase iron protein, mediated by the enzymes DraT and DraG. At least three pathways for indole-3-acetic acid (IAA) biosynthesis in A. brasilense exist: two Trp-dependent (the indole-3-pyruvic acid and presumably the indole-3-acetamide pathway) and one Trp-independent pathway. The occurrence of an IAA biosynthetic pathway not using Trp (tryptophan) as precursor is highly unusual in bacteria. Nevertheless, the indole-3-pyruvate decarboxylase encoding ipdC gene is crucial in the overall IAA biosynthesis in Azospirillum. A number of genes essential for Trp production have been isolated in A. brasilense, including trpE(G) which codes for anthranilate synthase, the key enzyme in Trp biosynthesis. The relevance of each of these four aspects for plant growth promotion by Azospirillum is discussed.
1,017 citations
TL;DR: N2-fixing bacteria such as Azoarcus spp.
474 citations
TL;DR: PCR and Western immunoblotting, using primers specific for eubacteria and antibodies recognizing type-specific antigens, indicated that strain BH72 could colonize rice plants systemically, probably mediated by longitudinal spreading through vessels.
Abstract: The invasive properties of Azoarcus sp. strain BH72, an endorhizospheric isolate of Kallar grass, on gnotobiotically grown seedlings of Oryza sativa IR36 and Leptochloa fusca (L.) Kunth were studied. Additionally, Azoarcus spp. were localized in roots of field-grown Kallar grass. To facilitate localization and to assure identity of bacteria, genetically engineered microorganisms expressing beta-glucuronidase were also used as inocula. beta-Glucuronidase staining indicated that the apical region of the root behind the meristem was the most intensively colonized. Light and electron microscopy showed that strain BH72 penetrated the rhizoplane preferentially in the zones of elongation and differentiation and colonized the root interior inter- and intracellularly. In addition to the root cortex, stelar tissue was also colonized; bacteria were found in the xylem. No evidence was obtained that Azoarcus spp. could reside in living plant cells; rather, plant cells were apparently destroyed after bacteria had penetrated the cell wall. A common pathogenicity test on tobacco leaves provided no evidence that representative strains of Azoarcus spp. are phytopathogenic. Compared with the control, inoculation with strain BH72 significantly promoted growth of rice seedlings. This effect was reversed when the plant medium was supplemented with malate (0.2 g/liter). N2 fixation was apparently not involved, because the same response was obtained with a nifK mutant of strain BH72, which has a Nif- phenotype. Also, Western blot (immunoblot) analysis of protein extracts from rice seedlings gave no indication that nitrogenase was present. PCR and Western immunoblotting, using primers specific for eubacteria and antibodies recognizing type-specific antigens, respectively, indicated that strain BH72 could colonize rice plants systemically, probably mediated by longitudinal spreading through vessels.
424 citations
TL;DR: High-throughput sequencing was used to reveal the community structures of nine coking wastewater treatment plants in China for the first time and indicated that operation mode, flow rate and temperature might be the key factors in community formation.
414 citations
TL;DR: Results indicate that Azoarcus sp.
Abstract: The extent to which the N2-fixing bacterial endophyte Azoarcus sp. strain BH72 in the rhizosphere of Kallar grass can provide fixed nitrogen to the plant was assessed by evaluating inoculated plants grown in the greenhouse and uninoculated plants taken from the natural environment. The inoculum consisted of either wild-type bacteria or nifK- mutant strain BHNKD4. In N2-deficient conditions, plants inoculated with strain BH72 (N2-fixing test plants) grew better and accumulated more nitrogen with a lower delta15N signature after 8 months than did plants inoculated with the mutant strain (non-N2-fixing control plants). Polyadenylated or polymerase chain reaction-amplified BH72 nifH transcripts were retrieved from test but not from control plants. BH72 nifH transcripts were abundant. The inocula could not be reisolated. These results indicate that Azoarcus sp. BH72 can contribute combined N2 to the plant in an unculturable state. Abundant BH72 nifH transcripts were detected also in uninoculated plants taken from the natural environment, from which Azoarcus sp. BH72 also could not be isolated. Quantification of nitrogenase gene transcription indicated a high potential of strain BH72 for biological N2 fixation in association with roots. Phylogenetic analysis of nitrogenase sequences predicted that uncultured grass endophytes including Azoarcus spp. are ecologically dominant and play an important role in N2-fixation in natural grass ecosystems.
303 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2022 | 2 |
| 2021 | 11 |
| 2020 | 10 |
| 2019 | 7 |
| 2018 | 7 |
| 2017 | 8 |