Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
A . zo . spi . ril ' lum . Fr. n. azote nitrogen; Gr. n. spira a spiral; M.L. dim. neut. n. spirillum a small spiral; Azospirillum a small nitrogen spiral. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Azospirillum Plump , slightly‐curved and straight rods , 0 . 6–1 . 7 × 2 . 1–3 . 8 µm , often with pointed ends. Intracellular granules of poly‐β‐hydroxybutyrate are present. Enlarged, pleomorphic forms may occur in old, alkaline cultures, under conditions of excess oxygen or other stress. Gram negative to Gram variable. Motile in liquid media by a single polar flagellum ; on solid media at 30°C, numerous lateral flagella of shorter wavelength may also be formed. Nitrogen fixers , exhibiting N 2 ‐dependent growth under microaerobic conditions . Grow well under an air atmosphere in the presence of a source of fixed nitrogen such as an ammonium or glutamate salts. Cells previously grown in presence of an inorganic nitrogen source may fix nitrogen in air provided that all added nitrogen is exhausted and nitrogenase is derepressed. Possess mainly a respiratory type of metabolism with oxygen and, with some strains, nitrate or nitrite as the terminal electron acceptor. Fermentative metabolism may also occur. Under severe oxygen limitation , some strains may dissimilate nitrate to nitrite or to nitrous oxide and nitrogen gas . Optimal temperature for growth varies from 33 to 41°C and pH from 5.5 to 7.5. Some strains may grow and form light or dark pink colonies, often wrinkled and non‐slimy, on potato agar. Oxidase positive. Chemoorganotrophic; some strains are facultative hydrogen autotrophs. Grow well on salts of organic acids such as malate , succinate , lactate or pyruvate . d ‐ fructose and certain carbohydrates may also serve as carbon sources . Some species require biotin. Growth in presence of 3% NaCl has been observed for some species. Occur free‐living in the soil or associated with the roots , stems , leaves , and seeds mainly of cereals and forage grasses, although they have also been isolated from coconut plants, vegetables, fruits, legume, and tuber plants. May also be found in freshwater lakes. Root nodules are not induced. The mol % G + C of the DNA is : 64–71. Type species : Azospirillum lipoferum (Beijerinck 1925) Tarrand, Krieg and Döbereiner 1979, 79 (Effective publication: Tarrand, Krieg and Döbereiner 1978, 978) ( Spirillum lipoferum Beijerinck 1925, 353.)
A . zo . spi . ril ' lum . Fr. n. azote nitrogen; Gr. n. spira a spiral; M.L. dim. neut. n. spirillum a small spiral; Azospirillum a small nitrogen spiral. Proteobacteria / Alphaproteobacteria / Rhodospirillales / Rhodospirillaceae / Azospirillum Plump , slightly‐curved and straight rods , 0 . 6–1 . 7 × 2 . 1–3 . 8 µm , often with pointed ends. Intracellular granules of poly‐β‐hydroxybutyrate are present. Enlarged, pleomorphic forms may occur in old, alkaline cultures, under conditions of excess oxygen or other stress. Gram negative to Gram variable. Motile in liquid media by a single polar flagellum ; on solid media at 30°C, numerous lateral flagella of shorter wavelength may also be formed. Nitrogen fixers , exhibiting N 2 ‐dependent growth under microaerobic conditions . Grow well under an air atmosphere in the presence of a source of fixed nitrogen such as an ammonium or glutamate salts. Cells previously grown in presence of an inorganic nitrogen source may fix nitrogen in air provided that all added nitrogen is exhausted and nitrogenase is derepressed. Possess mainly a respiratory type of metabolism with oxygen and, with some strains, nitrate or nitrite as the terminal electron acceptor. Fermentative metabolism may also occur. Under severe oxygen limitation , some strains may dissimilate nitrate to nitrite or to nitrous oxide and nitrogen gas . Optimal temperature for growth varies from 33 to 41°C and pH from 5.5 to 7.5. Some strains may grow and form light or dark pink colonies, often wrinkled and non‐slimy, on potato agar. Oxidase positive. Chemoorganotrophic; some strains are facultative hydrogen autotrophs. Grow well on salts of organic acids such as malate , succinate , lactate or pyruvate . d ‐ fructose and certain carbohydrates may also serve as carbon sources . Some species require biotin. Growth in presence of 3% NaCl has been observed for some species. Occur free‐living in the soil or associated with the roots , stems , leaves , and seeds mainly of cereals and forage grasses, although they have also been isolated from coconut plants, vegetables, fruits, legume, and tuber plants. May also be found in freshwater lakes. Root nodules are not induced. The mol % G + C of the DNA is : 64–71. Type species : Azospirillum lipoferum (Beijerinck 1925) Tarrand, Krieg and Döbereiner 1979, 79 (Effective publication: Tarrand, Krieg and Döbereiner 1978, 978) ( Spirillum lipoferum Beijerinck 1925, 353.)
The diversity and function of nitrogen-fixing bacteria colonizing rice roots are not well understood. A field experiment was conducted to determine the diversity of diazotrophic communities associated with roots of modern rice cultivars using culture-independent molecular analyses of nitrogenase gene (nifH) fragments. Experimental treatments included four modern rice cultivars (Oryza sativa, one Indica, one Japonica and two hybrid rice varieties) and three levels (0, 50, and 100 kg N ha(-1)) of N (urea) fertilizer application. Cloning and sequencing of 103 partial nifH genes showed that a diverse community of diazotrophs was associated with rice roots. However, the nifH gene fragments belonging to betaproteobacteria were dominant, accounting for nearly half of nifH sequences analyzed across the clone libraries. Most of them were similar to nifH fragments retrieved from wild rice and Kallar grass, with Azoarcus spp. being the closest cultured relatives. Alphaproteobacteria were also detected, but their relative abundance in the nifH gene pools was dramatically decreased with N fertilizer application. In addition, a high fraction of nifH gene pools was affiliated with methylotrophs and methane oxidizers. The sequence analysis was consistent with the terminal restriction fragment-length polymorphism (T-RFLP) fingerprinting of the nifH gene fragments, which showed three of four dominant terminal restriction fragments were mainly related to betaproteobacteria based on in silico digestion of nifH sequences. T-RFLP analyses also revealed that the effects of N fertilizer on the nifH gene diversity retrieved from roots varied according to rice cultivars. In summary, the present study revealed the prevalence of betaproteobacterial sequences among the proteobacteria associated with roots of modern rice cultivars. This group of diazotrophs appeared less sensitive to N fertilizer application than diazotrophic alphaproteobacteria. Furthermore, methylotrophs may also play a role in nitrogen fixation on rice roots. However, it must be noted that due to the potential bias of polymerase chain reaction protocol, the significance of non-proteobacterial diazotrophs such as Firmicutes and anaerobic bacteria is possibly underestimated.
Rhizosphere bacteria, whether phytopathogenic or phytobeneficial, are thought to be perceived by the plant as a threat. Plant Growth-Promoting Rhizobacteria (PGPR), such as many strains of the Azospirillum genus known as the main phytostimulator of cereals, cooperate with host plants and favorably affect their growth and health. An earlier study of rice root transcriptome, undertaken with two rice cultivars and two Azospirillum strains, revealed a strain-dependent response during the rice-Azospirillum association and showed that only a few genes, including some implicated in plant defense, were commonly regulated in all tested conditions. Here, a set of genes was selected from previous studies and their expression was monitored by qRT-PCR in rice roots inoculated with ten PGPR strains isolated from various plants and belonging to various genera (Azospirillum, Herbaspirillum, Paraburkholderia). A common expression pattern was highlighted for four genes that are proposed to be markers of the rice-PGPR interaction: two genes involved in diterpenoid phytoalexin biosynthesis (OsDXS3 and OsDTC2) and one coding for an uncharacterized protein (Os02g0582900) were significantly induced by PGPR whereas one defense-related gene encoding a pathogenesisrelated protein (PR1b, Os01g0382000) was significantly repressed. Interestingly, exposure to a rice bacterial pathogen also triggered the expression of OsDXS3 while the expression of Os02g0582900 and PR1b was downregulated, suggesting that these genes might play a key role in rice-bacteria interactions. Integration of these results with previous data led us to propose that the jasmonic acid signaling pathway might be triggered in rice roots upon inoculation with PGPR.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.