Denitrification in <i>Sinorhizobium meliloti</i>

Torres, María J.; Rubia, María Isabel; Bedmar, Eulogio J.; Delgado, Manuel Lorenzo

doi:10.1042/bst20110733

Cited by 31 publications

(29 citation statements)

References 35 publications

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“…That G. aurantiaca required the transient presence of O 2 for expression and activation of nitrous oxide reductases is nothing new. Ensifer meliloti strain 1021 was found to require partial oxygenation before activation of anaerobic denitrification and N 2 O reduction, and Paracoccus denitrificans exhibited the highest level of nosZ expression immediately following O 2 depletion (49,50). Nevertheless, the eventual termination of N 2 O reduction in prolonged anoxia has not been observed in these organisms.…”

Section: Discussionmentioning

confidence: 90%

Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27

Park

Kim

Yoon

2017

Appl Environ Microbiol

120

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N 2 O-reducing organisms with nitrous oxide reductases (NosZ) are known as the only biological sink of N 2 O in the environment. Among the most abundant nosZ genes found in the environment are nosZ genes affiliated with the understudied Gemmatimonadetes phylum. In this study, a unique regulatory mechanism of N 2 O reduction in Gemmatimonas aurantiaca strain T-27, an isolate affiliated with the Gemmatimonadetes phylum, was examined. Strain T-27 was incubated with N 2 O and/or O 2 as the electron acceptor. Significant N 2 O reduction was observed only when O 2 was initially present. When batch cultures of strain T-27 were amended with O 2 and N 2 O, N 2 O reduction commenced after O 2 was depleted. In a long-term incubation with the addition of N 2 O upon depletion, the N 2 O reduction rate decreased over time and came to an eventual stop. Spiking of the culture with O 2 resulted in the resuscitation of N 2 O reduction activity, supporting the hypothesis that N 2 O reduction by strain T-27 required the transient presence of O 2 . The highest level of nosZ transcription (8.97 nosZ transcripts/recA transcript) was observed immediately after O 2 depletion, and transcription decreased ϳ25-fold within 85 h, supporting the observed phenotype. The observed difference between responses of strain T-27 cultures amended with and without N 2 O to O 2 starvation suggested that N 2 O helped sustain the viability of strain T-27 during temporary anoxia, although N 2 O reduction was not coupled to growth. The findings in this study suggest that obligate aerobic microorganisms with nosZ genes may utilize N 2 O as a temporary surrogate for O 2 to survive periodic anoxia.IMPORTANCE Emission of N 2 O, a potent greenhouse gas and ozone depletion agent, from the soil environment is largely determined by microbial sources and sinks. N 2 O reduction by organisms with N 2 O reductases (NosZ) is the only known biological sink of N 2 O at environmentally relevant concentrations (up to ϳ1,000 parts per million by volume [ppmv]). Although a large fraction of nosZ genes recovered from soil is affiliated with nosZ found in the genomes of the obligate aerobic phylum Gemmatimonadetes, N 2 O reduction has not yet been confirmed in any of these organisms. This study demonstrates that N 2 O is reduced by an obligate aerobic bacterium, Gemmatimonas aurantiaca strain T-27, and suggests a novel regulation mechanism for N 2 O reduction in this organism, which may also be applicable to other obligate aerobic organisms possessing nosZ genes. We expect that these findings will significantly advance the understanding of N 2 O dynamics in environments with frequent transitions between oxic and anoxic conditions.

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Section: Discussionmentioning

confidence: 90%

Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27

Park

Kim

Yoon

2017

Appl Environ Microbiol

120

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“…The ability of rhizobia to denitrify depends on the nap , nir , nor , and nos gene clusters that encode nitrate-, nitrite-, nitric oxide-, and nitrous oxide-reductases, respectively [40,41]. Denitrification plays an important role in nitrogen-fixing soybean- Bradyrhizobium japonicum symbiosis and S. meliloti has been shown to denitrify under free-living and symbiotic conditions [41].…”

Section: Resultsmentioning

confidence: 99%

Comparative genomics of the core and accessory genomes of 48 Sinorhizobium strains comprising five genospecies

et al. 2013

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BackgroundThe sinorhizobia are amongst the most well studied members of nitrogen-fixing root nodule bacteria and contribute substantial amounts of fixed nitrogen to the biosphere. While the alfalfa symbiont Sinorhizobium meliloti RM 1021 was one of the first rhizobial strains to be completely sequenced, little information is available about the genomes of this large and diverse species group.ResultsHere we report the draft assembly and annotation of 48 strains of Sinorhizobium comprising five genospecies. While S. meliloti and S. medicae are taxonomically related, they displayed different nodulation patterns on diverse Medicago host plants, and have differences in gene content, including those involved in conjugation and organic sulfur utilization. Genes involved in Nod factor and polysaccharide biosynthesis, denitrification and type III, IV, and VI secretion systems also vary within and between species. Symbiotic phenotyping and mutational analyses indicated that some type IV secretion genes are symbiosis-related and involved in nitrogen fixation efficiency. Moreover, there is a correlation between the presence of type IV secretion systems, heme biosynthesis and microaerobic denitrification genes, and symbiotic efficiency.ConclusionsOur results suggest that each Sinorhizobium strain uses a slightly different strategy to obtain maximum compatibility with a host plant. This large genome data set provides useful information to better understand the functional features of five Sinorhizobium species, especially compatibility in legume-Sinorhizobium interactions. The diversity of genes present in the accessory genomes of members of this genus indicates that each bacterium has adopted slightly different strategies to interact with diverse plant genera and soil environments.

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“…The genetic determinants for expression of NirK and cNor are present in R. etli CFN42 (Bueno, Gomez-Hernandez, Girard, Bedmar, & Delgado, 2005;Gomez-Hernandez et al, 2011). E. meliloti (formerly Sinorhizobium meliloti) (Galibert et al, 2001;Holloway, McCormick, Watson, & Chan, 1996;Torres et al, 2011) and B. japonicum (recently reclassified as Bradyrhizobium diazoefficiens USDA 110, Delamuta et al, 2013;Bedmar et al, 2005;Kaneko et al, 2002) contain nap, nirK, nor and nos genes (http://www.kazusa.or.jp/rhizobase). Among them, B. japonicum is the only rhizobial species that has the ability to grow under anoxic conditions with nitrate through denitrification pathway and where this process has been extensively investigated not only under free-living but also under symbiotic conditions (for reviews, see Bedmar et al, 2013;Bedmar et al, 2005;Delgado, Casella, & Bedmar, 2007;Sanchez, Cabrera, et al, 2011).…”

Section: B Japonicum As a Model Of Legume-associated Rhizobial Denitmentioning

confidence: 99%

“…Similarly to many other denitrifiers, expression of denitrification genes in B. japonicum requires both oxygen limitation and the presence of nitrate or a derived NOx . In this bacterium, perception and transduction of the 'low oxygen signal' are mediated by two interlinked oxygen responsive regulatory cascades, the FixLJ-FixK 2 -NnrR and the RegSR-NifA (reviewed by Bueno et al, 2012;Torres et al, 2011;Fig. 10).…”

Section: Regulation Of B Japonicum Denitrificationmentioning

confidence: 99%

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria

Torres

Simon

Rowley

et al. 2016

Advances in Bacterial Electron Transport Systems and Their Regulation

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Nitrous oxide (N2O) is an important greenhouse gas (GHG) with substantial global warming potential and also contributes to ozone depletion through photochemical nitric oxide (NO) production in the stratosphere. The negative effects of N2O on climate and stratospheric ozone make N2O mitigation an international challenge. More than 60% of global N2O emissions are emitted from agricultural soils mainly due to the application of synthetic nitrogen-containing fertilizers. Thus, mitigation strategies must be developed which increase (or at least do not negatively impact) on agricultural efficiency whilst decrease the levels of N2O released. This aim is particularly important in the context of the ever expanding population and subsequent increased burden on the food chain. More than two-thirds of N2O emissions from soils can be attributed to bacterial and fungal denitrification and nitrification processes. In ammonia-oxidizing bacteria, N2O is formed through the oxidation of hydroxylamine to nitrite. In denitrifiers, nitrate is reduced to N2 via nitrite, NO and N2O production. In addition to denitrification, respiratory nitrate ammonification (also termed dissimilatory nitrate reduction to ammonium) is another important nitrate-reducing mechanism in soil, responsible for the loss of nitrate and production of N2O from reduction of NO that is formed as a by-product of the reduction process. This review will synthesize our current understanding of the environmental, regulatory and biochemical control of N2O emissions by nitrate-reducing bacteria and point to new solutions for agricultural GHG mitigation.

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Denitrification in Sinorhizobium meliloti

Cited by 31 publications

References 35 publications

Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27

Nitrous Oxide Reduction by an Obligate Aerobic Bacterium, Gemmatimonas aurantiaca Strain T-27

Comparative genomics of the core and accessory genomes of 48 Sinorhizobium strains comprising five genospecies

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria

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