Ineffectiveness of viomycin-resistant mutants of Rhizobium meliloti

Under clearly defined conditions one-step acquisition of viomycin resistance by a normally effective strain of Rhizobium meliloti resulted in one-step acquisition of ineffectiveness in nitrogen fixation, which probably occurred with a one-gene change in the R. meliloti genome. Two-step mutants retained their ability to produce root nodules but such nodules also were ineffective. Increased sensitivity of the viomycin-resistant mutants to glycine and D-alanine was not noted. Bacteroids were not seen in nodules formed by the viomycin-resistant mutants on their homologous host plant. Nitrogenase activity was not detected, by acetylene reduction, in detached ineffective nodules, whereas effective nodules formed 10.6 μmoles of ethylene per hour per gram of nodules. Growth of the effective parent strain in a low concentration of viomycin resulted in elongation and swelling of the cells so that they appeared as artificially produced bacteroids. Viomycin-resistant mutants did not undergo this transformation. Antigens could be readily extracted by hot- and cold-saline extraction of wet packed cells of both resistant and sensitive cultures but antigenic differences, which may have indicated cell wall differences, were not noted.

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Phenotypic reversion of nitrogenase in pleiotropic mutants of Rhizobium meliloti

Canadian Journal of Microbiology ◽

10.1139/m79-048 ◽

1979 ◽

Vol 25 (3) ◽

pp. 298-301 ◽

Cited By ~ 3

Author(s):

Ilona Barabás ◽

Tibor Sik

Keyword(s):

Amino Acids ◽

Nitrogen Fixation ◽

Nitrate Reductase ◽

Nitrate Reductase Activity ◽

Symbiotic Nitrogen Fixation ◽

Rhizobium Meliloti ◽

Nitrogenase Activity ◽

Reductase Activity ◽

Amino Acid Utilization ◽

Phenotypic Reversion

In two out of three pleiotropic mutants of Rhizobium meliloti, defective in nitrate reductase induced by amino acid utilization in vegetative bacteria and in symbiotic nitrogen fixation, nitrogenase activity could be restored completely by purines and partially by the amino acids L-glutamate, L-aspartate, L-glutamine, and L-asparagine. The compounds restoring effectiveness in nitrogen fixation did not restore nitrate reductase activity in vegetative bacteria. The restoration of effectiveness supports our earlier conclusion that the mutation is not in the structural gene for a suggested common subunit of nitrogenase and nitrate reductase.

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Studies on associative nitrogen fixation by antibiotic-resistant mutants ofAzospirillum brasilensewith genotypes of lentil (Lens culinaris)Rhizobiumstrains in calcareous soil

The Journal of Agricultural Science ◽

10.1017/s0021859600043136 ◽

1985 ◽

Vol 104 (1) ◽

pp. 207-215 ◽

Cited By ~ 1

Author(s):

R. Rai

Keyword(s):

Nitrogen Fixation ◽

Azospirillum Brasilense ◽

Calcareous Soil ◽

Lens Culinaris ◽

Nitrogenase Activity ◽

Dry Weight ◽

Antibiotic Resistant ◽

Uninoculated Control ◽

Resistant Mutants ◽

Antibiotic Resistant Mutants

SummaryNitrosoguanidine-induced mutation frequencies for resistance to streptomycin, spectinomycin, erythromycin and novomycin were studied inAzospirillum brasilense.Lentil inoculated withA. brasilenseand its mutants andRhizobiumstrains produced increased nodule dry weight, nitrogenase activity of nodules and roots and grain yield compared with an uninoculated control.

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Morphology and Nitrogenase Activity of Agar Cultures and Root Nodules Formed by D-Cycloserine-resistant Mutants of Rhizobium sp. Strain 32H1

Journal of General Microbiology ◽

10.1099/00221287-110-1-177 ◽

1979 ◽

Vol 110 (1) ◽

pp. 177-184 ◽

Cited By ~ 2

Author(s):

C. E. Pankhurst ◽

A. S. Craig

Keyword(s):

Nitrogenase Activity ◽

Root Nodules ◽

Resistant Mutants ◽

Rhizobium Sp

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Effects of Engineered Sinorhizobium meliloti on Cytokinin Synthesis and Tolerance of Alfalfa to Extreme Drought Stress

Applied and Environmental Microbiology ◽

10.1128/aem.01276-12 ◽

2012 ◽

Vol 78 (22) ◽

pp. 8056-8061 ◽

Cited By ~ 32

Author(s):

Ji Xu ◽

Xiao-Lin Li ◽

Li Luo

Keyword(s):

Nitrogen Fixation ◽

Drought Stress ◽

Sinorhizobium Meliloti ◽

Nitrogenase Activity ◽

Root Nodules ◽

Severe Drought ◽

Control Strain ◽

Free Living ◽

Content Type ◽

Host Tolerance

ABSTRACTCytokinin is required for the initiation of leguminous nitrogen fixation nodules elicited by rhizobia and the delay of the leaf senescence induced by drought stress. A few free-living rhizobia have been found to produce cytokinin. However, the effects of engineered rhizobia capable of synthesizing cytokinin on host tolerance to abiotic stresses have not yet been described. In this study, two engineeredSinorhizobiumstrains overproducing cytokinin were constructed. The tolerance of inoculated alfalfa plants to severe drought stress was assessed. The engineered strains, which expressed theAgrobacterium iptgene under the control of different promoters, synthesized more zeatins than the control strain under free-living conditions, but their own growth was not affected. After a 4-week inoculation period, the effects of engineered strains on alfalfa growth and nitrogen fixation were similar to those of the control strain under nondrought conditions. After being subjected to severe drought stress, most of the alfalfa plants inoculated with engineered strains survived, and the nitrogenase activity in their root nodules showed no apparent change. A small elevation in zeatin concentration was observed in the leaves of these plants. The expression of antioxidant enzymes increased, and the level of reactive oxygen species decreased correspondingly. Although theiptgene was transcribed in the bacteroids of engineered strains, the level of cytokinin in alfalfa nodules was identical to that of the control. These findings suggest that engineeredSinorhizobiumstrains synthesizing more cytokinin could improve the tolerance of alfalfa to severe drought stress without affecting alfalfa nodulation or nitrogen fixation.

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Characteristics of some single-step mutants to chloramphenicol resistance in Escherichia coli K12 and their interactions with R-factor genes

Genetics Research ◽

10.1017/s0016672300009708 ◽

1966 ◽

Vol 7 (2) ◽

pp. 281-286 ◽

Cited By ~ 11

Author(s):

E. C. R. Reeve

Keyword(s):

Escherichia Coli ◽

Single Step ◽

Chloramphenicol Resistance ◽

R Factor ◽

Resistance Patterns ◽

One Step ◽

Increased Sensitivity ◽

Resistant Mutants ◽

High Level ◽

R Factors

Six one-step Chloramphenicol (Cm)-resistant mutants of Escherichia coli K12 were graded for resistance to Cm, Tetracycline (Tc) and Puromyein (Pm) by streaking on minimal agar plates containing antibiotic. They fell into at least three distinct groups on the basis of their resistance patterns. One mutant showed increased sensitivity to Pm. Most of the mutants expressed their effect on resistance to Cm and Tc in the presence of R-factors carrying resistance genes for these antibiotics, but one mutant with a relatively high level of resistance to Cm had its resistance effect completely masked in the presence of R-mediated resistance. Similar cases were found among mutants selected for Cm-resistance in another strain of K12.

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Renodulation and nitrogen fixing potential of Acacia nilotica inoculated with Rhizobium isolates

Canadian Journal of Microbiology ◽

10.1139/m93-012 ◽

1993 ◽

Vol 39 (1) ◽

pp. 87-91 ◽

Cited By ~ 8

Author(s):

Banwari Lal ◽

Sunil Khanna

Keyword(s):

Nitrogen Fixation ◽

Dry Matter ◽

Nitrogenase Activity ◽

Root Nodules ◽

Acacia Nilotica ◽

Resistance Pattern ◽

Dry Matter Yield ◽

Native Population ◽

Rhizobium Isolate ◽

Matter Production

Renodulation and nitrogen fixation potential of indigenous and exotic isolates of Rhizobium were studied in a field experiment with Acacia nilotica from July 1990 to June 1991. The inoculum isolates belonged to different serotypes and did not show cross-reaction with the native population of Rhizobium. Nitrogenase activity of root nodules observed at 4-month intervals covering three seasons snowed a decline during winter months, which corresponded with the senescence of the nodules. Maximal renodulation as checked by serotyping and antibiotic resistance pattern was observed with isolate AB 3 followed by AD 4 and USDA 3325. The highest nitrogenase activity was exhibited in plants inoculated with AD 4 at 12 months. Plants inoculated with Rhizobium isolate USDA 3325 showed the highest increase in dry-matter yield at 12 months. Except for AB 3, dual inoculation with Rhizobium isolates and Glomus fasciculatum did not enhance dry matter production as compared with uninoculated controls or single inoculation of either Rhizobium isolate or G. fasciculatum.Key words: Rhizobium, Acacia nilotica, nitrogenase activity, renodulation.

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Introduction of H2-Uptake Hydrogenase Genes Into Rhizobial Strains Improves Symbiotic Nitrogen Fixation in Vicia sativa and Lotus corniculatus Forage Legumes

Frontiers in Agronomy ◽

10.3389/fagro.2021.661534 ◽

2021 ◽

Vol 3 ◽

Author(s):

Mariana Sotelo ◽

Ana Claudia Ureta ◽

Socorro Muñoz ◽

Juan Sanjuán ◽

Jorge Monza ◽

...

Keyword(s):

Nitrogen Fixation ◽

Rhizobium Leguminosarum ◽

Symbiotic Nitrogen Fixation ◽

Nitrogenase Activity ◽

Root Nodules ◽

Lotus Corniculatus ◽

Vicia Sativa ◽

Uptake Hydrogenase ◽

Forage Crops ◽

Mesorhizobium Loti

Biological nitrogen fixation by the Rhizobium-legume symbiosis allows the conversion of atmospheric nitrogen into ammonia within root nodules mediated by the nitrogenase enzyme. Nitrogenase activity results in the evolution of hydrogen as a result of a side reaction intrinsic to the activity of this enzyme. Some rhizobia, and also other nitrogen fixers, induce a NiFe uptake hydrogenase (Hup) to recycle hydrogen produced by nitrogenase, thus improving the efficiency of the nitrogen fixation process. In this work we report the generation and symbiotic behavior of hydrogenase-positive Rhizobium leguminosarum and Mesorhizobium loti strains effective in vetch (Vicia sativa) and birsfoot trefoil (Lotus corniculatus) forage crops, respectively. The ability of hydrogen recycling was transferred to these strains through the incorporation of hup minitransposon TnHB100, thus leading to full recycling of hydrogen in nodules. Inoculation of Vicia and Lotus plants with these engineered strains led to significant increases in the levels of nitrogen incorporated into the host legumes. The level of improvement of symbiotic performance was dependent on the recipient strain and also on the legume host. These results indicate that hydrogen recycling has the potential to improve symbiotic nitrogen fixation in forage plants.

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MtMOT1.2 is responsible for molybdate supply toMedicago truncatulanodules

10.1101/272112 ◽

2018 ◽

Author(s):

Patricia Gil-Díez ◽

Manuel Tejada-Jiménez ◽

Javier León-Mediavilla ◽

Jiangqi Wen ◽

Kirankumar S. Mysore ◽

...

Keyword(s):

Nitrogen Fixation ◽

Symbiotic Nitrogen Fixation ◽

Nitrogenase Activity ◽

Reductase Activity ◽

Root Nodules ◽

Loss Of Function ◽

Intracellular Membrane ◽

Wild Type ◽

Endodermal Cells ◽

Iron Molybdenum Cofactor

ABSTRACTSymbiotic nitrogen fixation in legume root nodules requires a steady supply of molybdenum for synthesis of the iron-molybdenum cofactor of nitrogenase. This nutrient has to be provided by the host plant from the soil, crossing several symplastically disconnected compartments through molybdate transporters, including members of the MOT1 family. MtMOT1.2 is aMedicago truncatulaMOT1 family member located in the endodermal cells in roots and nodules. Immunolocalization of a tagged MtMOT1.2 indicates that it is associated to the plasma membrane and to intracellular membrane systems, where it would be transporting molybdate towards the cytosol, as indicated in yeast transport assays. A loss-of-functionmot1.2-1mutant showed reduced growth compared to wild-type plants when nitrogen fixation was required, but not when nitrogen was provided as nitrate. While no effect on molybdenum-dependent nitrate reductase activity was observed, nitrogenase activity was severely affected, explaining the observed difference of growth depending on nitrogen source. This phenotype was the result of molybdate not reaching the nitrogen-fixing nodules, since genetic complementation with a wild-typeMtMOT1.2gene or molybdate-fortification of the nutrient solution, both restored wild-type levels of growth and nitrogenase activity. These results support a model in which MtMOT1.2 would mediate molybdate delivery by the vasculature into the nodules.

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Nitrogen Fixation by Native Australian Legumes

Australian Journal of Botany ◽

10.1071/bt9810143 ◽

1981 ◽

Vol 29 (2) ◽

pp. 143 ◽

Cited By ~ 33

Author(s):

AC Lawrie

Keyword(s):

Nitrogen Fixation ◽

Acetylene Reduction ◽

Sand Dune ◽

Nitrogenase Activity ◽

Root Nodules ◽

Sand Dunes ◽

Late Summer ◽

Open Forest ◽

Seasonal And Diurnal Variations ◽

Major Factors

Nitrogen fixation was studied by the acetylene-reduction technique in root nodules of 10 native Australian legumes in three habitats in Victoria: low open-forest. sandy heathland and coastal sand dunes. Nodular activity reached a maximum in spring (and in autumn in sand-dune species), declined to a minimum in late summer and continued at a low level throughout winter. Mean nitrogenase activity was 1.73 μmol C2H2 reduced g-1 fresh wt nodules h-1, with spring maxima 8-250 times summer minima. It is suggested that variations in rainfall and temperature were the major factors influencing seasonal variations in nodular activity. Estiniates of minimum acetylene reduction per hectare per year were derived from measurements of seasonal and diurnal variations in acetylene reduction and abundance of nodules per hectare, and were used to derive approximate minimum values for nitrogen fixation of 0.004-0.746 kg ha-1 yr-1. The quantities of nitrogen fixed are compared with other reports and the significance of nitrogen fixation by these native legumes is discussed.

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