Generation of
 Bradyrhizobium japonicum
 Mutants with Increased N
 2
 O Reductase Activity by Selection after Introduction of a Mutated
 dnaQ
 Gene

Itakura, Manabu; Tabata, Kazufumi; Eda, Shima; Mitsui, Hisayuki; Murakami, Kiriko; Yasuda, Junichi; Minamisawa, Kiwamu

doi:10.1128/aem.01850-08

Cited by 31 publications

(33 citation statements)

References 45 publications

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“…The relationship between inoculation of nosZ+ strains and N 2 O emissions from soybean ecosystems was investigated in a pot study (Hénault and Revellin 2011) in which a significant reduction in N 2 O concentrations was observed when nodules sampled from the soybean plants inoculated at the pod-filling stage were incubated at 10 μL l −1 N 2 O. Based on the assumption that nosZ expression was the key to mitigating N 2 O emissions from soybean root systems, Itakura et al (2008) produced mutants of B. japonicum strains with increased N 2 O reductase activity (nosZ++ strains). This was achieved by increasing the encoding activity of nosZ.…”

Section: A New Methods For Mitigation Of Postharvest N 2 O Emissions Fmentioning

confidence: 99%

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

Uchida

Akiyama

2013

Soil Science and Plant Nutrition

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In this review, the current knowledge of nitrous oxide (N 2 O) emissions from soybean (Glycine max (L.) Merr.) ecosystems, particularly on postharvest N 2 O emissions, is summarized and controlling factors of postharvest N 2 O emissions from soybean ecosystems are discussed. A new biological method to mitigate N 2 O emission is also presented. The latest (2006) guidelines of the Intergovernmental Panel on Climate Change (IPCC) concluded that N 2 O emissions derived directly from biological nitrogen (N) fixation were not significant in legume crop ecosystems. The default N 2 O emission factor from biological N fixation was revised to zero, whereas the default N 2 O emission factor for the decomposition of legume crop residues (postharvest N 2 O emissions) was the same as that for nonlegume crop residues (1%). From previously measured field data, the percentage of N in soybean residue emitted as N 2 O after harvest was calculated to determine emission factors. Values ranged from 0.0-10.0% (average 1.3% ± 2.7%, median: 0.2%), indicating relatively low emission factors. The average emission factor calculated for N 2 O emissions from N in soybean residues was slightly higher than the default emission factor for N in crop residue specified in the guidelines. However, the volume of field-measured postharvest N 2 O emissions in soybean ecosystems is low compared with data for N 2 O emissions during the crop growing season. Previous field-measured data demonstrated that N 2 O emissions often peaked sharply immediately after the harvest. However, values for N 2 O fluxes in the currently available field data were determined on a weekly or monthly basis. This large time gap between samplings may have resulted in underestimation of postharvest N 2 O emissions in soybean ecosystems. More detailed field studies on postharvest N 2 O emissions from soybean ecosystems are needed. Nodule decomposition is the major source of postharvest N 2 O emissions in soybean ecosystems. A new microbiological method was recently developed to mitigate postharvest N 2 O emissions from soybean ecosystems utilizing N-fixing bacteria with increased N 2 O-reducing activity (increased expression of nosZ). This approach may potentially be applied to other leguminous crops and non-legume ecosystems. Ongoing research on the relationships between soil N 2 O emissions and nosZ may reveal a new method for N 2 O mitigation in the future.

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Section: A New Methods For Mitigation Of Postharvest N 2 O Emissions Fmentioning

confidence: 99%

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

Uchida

Akiyama

2013

Soil Science and Plant Nutrition

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“…There are several other experiments in which bacterial disparity-mutators displayed high adaptabilities to different conditions and showed genome-wide improvements [25][26][27] .…”

Section: Escherichia Coli Mutatormentioning

confidence: 99%

The role of disparity-mutagenesis model on tumor development with special reference to increased mutation rate

Furusawa¹

2013

JST

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Human solid tumors are believed to have very high mutation rates at least in the early stage of extension. Irrespective of whether the increased mutation rate is a necessary condition for the tumor development or not, extremely high mutation rates such as in excess of the so-called "threshold" would before long result in the natural death of tumor cells. In reality, however, we are dying by cancer. Thus, it has been hypothesized that tumor cells should make a quick transition from the higher mutation state to the lower one. According to our "disparity-mutagenesis model", however, carcinogenesis could continue without any incident even under a prolonged period of high mutation rates. Namely, if lagging-strand-biased mutations far beyond the threshold of mutation rate are introduced in tumor cells, the tumor could progress to malignant extension without extinction. The results of evolution experiments using mutator microorganisms are discussed in terms of carcinogenesis.

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“…A B. japonicum mutant, 5M09, with increased N 2 O reductase activity (Nos ϩϩ ) was isolated through the impairment of proofreading activity and the use of enrichment culture under selection pressure for N 2 O respiration (8). Recently, it was shown that postharvest N 2 O emissions from soybean fields can be mitigated by inoculation with 5M09 at the field scale (9).…”

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confidence: 99%

“…A B. japonicum mutant (PRNOS) that overexpresses the nos genes as controlled by the rRNA gene promoter (9) was used as a Nos ϩϩ reference. B. japonicum USDA110 (United States Department of Agriculture, Beltsville, MD) and the mutant derivative strains 5M09 (8) and PRNOS (9) were used in this study. The bacterial strains and plasmids used in this work are listed in Table S1 in the supplemental material.…”

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confidence: 99%

Linked Expressions of nap and nos Genes in a Bradyrhizobium japonicum Mutant with Increased N ₂ O Reductase Activity

Sánchez¹,

Itakura²,

Mitsui³

et al. 2013

Appl Environ Microbiol

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To understand the mechanisms underlying the increased N 2 O reductase activity in the Bradyrhizobium japonicum 5M09 mutant from enrichment culture under N 2 O respiration, we analyzed the expression of genes encoding denitrification reductases and regulators. Our results suggest a common regulation of nap (encoding periplasmic nitrate reductase) and nos (encoding N 2 O reductase). N itrous oxide (N 2 O) is a key greenhouse gas that also damages the ozone layer. Soybean nodules emit N 2 O under field conditions in the late growth period (1-3). While N 2 O generation is due to a diversity of microbial enzymes, N 2 O consumption appears to be due exclusively to N 2 O reductase (Nos) (4-6). Nos catalyzes the two-electron reduction of N 2 O to N 2 . In strain USDA110 of the soybean symbiont Bradyrhizobium japonicum, the complete reduction of nitrate to N 2 depends on napEDABC (which encode periplasmic nitrate reductase [Nap]), nirK (copper-containing nitrite reductase [NirK]), norCBQD (c-type nitric oxide reductase [cNor]), and nosRZDYFLX (Nos) (7).A B. japonicum mutant, 5M09, with increased N 2 O reductase activity (Nos ϩϩ ) was isolated through the impairment of proofreading activity and the use of enrichment culture under selection pressure for N 2 O respiration (8). Recently, it was shown that postharvest N 2 O emissions from soybean fields can be mitigated by inoculation with 5M09 at the field scale (9). Because the mechanisms underlying the increased Nos activity in 5M09 remain unclear, the main objective of this work was to evaluate the expression of genes encoding denitrification reductases and regulators in 5M09. A B. japonicum mutant (PRNOS) that overexpresses the nos genes as controlled by the rRNA gene promoter (9) was used as a Nos ϩϩ reference. B. japonicum USDA110 (United States Department of Agriculture, Beltsville, MD) and the mutant derivative strains 5M09 (8) and PRNOS (9) were used in this study. The bacterial strains and plasmids used in this work are listed in Table S1 in the supplemental material. Cells were routinely cultured at 30°C in HM salt medium (10) supplemented with 0.1% arabinose, 0.025% (wt/vol) yeast extract, and trace metals (HMM medium) (11). For ␤-galactosidase assays, methyl viologen (MV)-dependent nitrate reductase assays, and RNA isolation, aerobically grown cells were collected and washed twice. They were then adjusted to an optical density at 660 nm of about 0.1 by the addition of HMM medium. Cells (10 ml) were incubated for 24 h in 120-ml airtight vials with air (aerobic conditions) or N 2 (anaerobic conditions). Where appropriate, either N 2 O (1%, 5%, 20%, or 25% [vol/vol]) or KNO 3 (10 or 20 mM) was added.For ␤-galactosidase assays, we used chromosomally integrated transcriptional lacZ fusions with the napE, nirK, norC, and nosZ promoters. The plasmids pBG0614 (12), pRJ2498 (13), pRJ2499 (13), and pNOSLZch were integrated by homologous recombination into the chromosome of each of USDA110 and 5M09. ␤-Galactosidase activity was determined with permeabilized cells as descri...

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Generation of Bradyrhizobium japonicum Mutants with Increased N ₂ O Reductase Activity by Selection after Introduction of a Mutated dnaQ Gene

Cited by 31 publications

References 45 publications

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

The role of disparity-mutagenesis model on tumor development with special reference to increased mutation rate

Linked Expressions of nap and nos Genes in a Bradyrhizobium japonicum Mutant with Increased N ₂ O Reductase Activity

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Generation of Bradyrhizobium japonicum Mutants with Increased N 2 O Reductase Activity by Selection after Introduction of a Mutated dnaQ Gene

Cited by 31 publications

References 45 publications

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

The role of disparity-mutagenesis model on tumor development with special reference to increased mutation rate

Linked Expressions of nap and nos Genes in a Bradyrhizobium japonicum Mutant with Increased N 2 O Reductase Activity

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Generation of Bradyrhizobium japonicum Mutants with Increased N ₂ O Reductase Activity by Selection after Introduction of a Mutated dnaQ Gene

Linked Expressions of nap and nos Genes in a Bradyrhizobium japonicum Mutant with Increased N ₂ O Reductase Activity