Acetylene reduction (nitrogen fixation) in a Delaware, USA salt marsh

Symbiotic nitrogen fixation may be limited by the transport of C4 dicarboxylates into bacteroids in the nodule for use as a carbon and energy source. In an attempt to increase dicarboxylate transport, a plasmid was constructed in which the Rhizobium meliloti structural transport gene dctA was fused to a tryptophan operon promoter from Salmonella typhimurium, trpPO. This resulted in a functional dctA gene that was no longer under the control of the dctBD regulatory genes, but the recombinant plasmid was found to be unstable in R. meliloti. To stably integrate the trpPO-dctA fusion, it was recloned into pBR325 and recombined into the R. meliloti exo megaplasmid in the dctABD region. The resultant strain showed constitutive dctA-specific mRNA synthesis which was about 5-fold higher than that found in fully induced wild-type cells. Uptake assays showed that [14C]succinate transport by the trpPO-dctA fusion strain was constitutive, and the transport rate was the same as that of induced control cells. Acetylene reduction assays indicated a significantly higher rate of nitrogen fixation in plants inoculated with the trpPO-dctA fusion strain compared with the control. Despite this apparent increase, the plants had the same top dry weights as those inoculated with control cells. Key words: acetylene reduction, genetic engineering, nodule, plasmid stability, promoter.

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Nitrogen fixation associated with 'Park' Kentucky bluegrass (Poapratensis L.)

Canadian Journal of Microbiology ◽

10.1139/m79-186 ◽

1979 ◽

Vol 25 (10) ◽

pp. 1197-1200 ◽

Cited By ~ 8

Author(s):

R. C. Shearman ◽

W. L. Pedersen ◽

R. V. Klucas ◽

E. J. Kinbacher

Keyword(s):

Nitrogen Fixation ◽

Acetylene Reduction ◽

Poa Pratensis ◽

Kentucky Bluegrass ◽

Acetylene Reduction Activity ◽

Controlled Environment ◽

Nitrogen Accumulation ◽

Reduction Activity ◽

Significant Difference ◽

Reduction Assay

Associative nitrogen fixation in Kentucky bluegrass (Poa pratensis L.) turfs inoculated with five nitrogen-fixing bacterial isolates was evaluated using the acetylene reduction assay and nitrogen accumulation as indicators of fixation. 'Park' and 'Nugget' Kentucky bluegrass turfs were grown in controlled environment chambers and inoculated with Klebsiella pneumoniae (W-2, W-6, and W-14), Erwinia herbicola (W-8), and Enterobacter cloacae (W-11). 'Park' inoculated with K. pneumoniae (W-6) had significant acetylene reduction activity using undisturbed turfs. Other treatments including turfs treated with heat-killed cells had no significant difference in acetylene reduction. In a second study, 'Park' and 'South Dakota Certified' turfs were grown in a greenhouse and inoculated with K. pneumoniae (W-6) and E. herbicola (W-8). 'Park' inoculated with K. pneumoniae (W-6) had increased acetylene reduction activity rates and also a greater nitrogen accumulation in aerial tissues when compared to controls. Acetylene reduction activity was correlated (r = 0.92) to nitrogen accumulation. Other treatments did not effectively increase acetylene reduction activity or nitrogen accumulation.

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Field measurement of symbiotic nitrogen fixation in an established lucerne ley using15N and an acetylene reduction method

Plant and Soil ◽

10.1007/bf02149828 ◽

1987 ◽

Vol 97 (1) ◽

pp. 93-104 ◽

Cited By ~ 10

Author(s):

M. Wivstad ◽

A. M. Mårtensson ◽

H. D. Ljunggren

Keyword(s):

Nitrogen Fixation ◽

Acetylene Reduction ◽

Field Measurement ◽

Reduction Method ◽

Symbiotic Nitrogen Fixation

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Nitrogen fixation (acetylene reduction) by Klebsiella pneumoniae in association with 'Park' Kentucky bluegrass (Poa pratensis L.)

Canadian Journal of Microbiology ◽

10.1139/m81-008 ◽

1981 ◽

Vol 27 (1) ◽

pp. 52-56 ◽

Cited By ~ 12

Author(s):

L. V. Wood ◽

R. V. Klucas ◽

R. C. Shearman

Keyword(s):

Nitrogen Fixation ◽

Klebsiella Pneumoniae ◽

Ethylene Production ◽

Acetylene Reduction ◽

Nitrogenase Activity ◽

Poa Pratensis ◽

Kentucky Bluegrass ◽

Surface Sterilization ◽

Reducing Activity ◽

Acetylene Reducing Activity

Turfs of 'Park' Kentucky bluegrass reestablished in the greenhouse and inoculated with Klebsiella pneumoniae (W6) showed significantly increased nitrogen fixation (acetylene reduction) compared with control turfs. Mean ethylene production rates per pot were 368 nmol h−1 for K. pneumoniae treated turfs, 55 nmol h−1 for heat-killed K. pneumoniae treated turfs, and 44 nmol h−1 for untreated turfs. Calculated lag periods before activity was observed were generally very short (less than 1 h).When 'Park' Kentucky bluegrass was grown from seed on soil-less medium of Turface, a fired aggregate clay, inoculation with K. pneumoniae (W6) resulted in 9 of 11 turfs showing nitrogenase activity (mean ethylene producion rate per pot was 195 nmol h−1). Only 3 of 11 turfs treated with heat-killed K. pneumoniae showed any activity and their mean rate of ethylene production (40 nmol h−1 per pot) was significantly lower than that for turfs treated with K. pneumoniae.Using the 'Park'–Turface soil-less model system it was shown that acetylene reducing activity was (i) root associated, (ii) generally highest at a depth of 1–4 cm below the surface, (iii) enhanced by washing excised roots, and (iv) inhibited by surface sterilization of excised roots. Klebsiella pneumoniae was recovered from Turface and roots showing acetylene reducing activity.

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