Root-Associated N ₂ Fixation (Acetylene Reduction) by Enterobacteriaceae and Azospirillum Strains in Cold-Climate Spodosols

Abstract

N2 fixation by bacteria in associative symbiosis with washed roots of 13 Poaceae and 8 other noncultivated plant species in Finland was demonstrated by the acetylene reduction method. The roots most active in C2H2 reduction were those of Agrostis stolonifera, Calamagrostis lanceolata, Elytrigia repens, and Phalaris arundinacea, which produced 538 to 1,510 nmol of C2H14 g-1 (dry weight). h-1 when incubated at PO2 0.04 with sucrose (pH 6.5), and 70 to 269 nmol of C2H4. g' (dry weight) h-' without an added energy source and unbuffered. Azospirillum lipferum, Enterobacter agglomerans, Klebsiella pneumoniae, and a Pseudomonas sp. were the acetylene-reducing organisms isolated. The results demonstrate the presence of N2-fixing organisms in associative symbiosis with plant roots found in a northern climatic region in acidic soils ranging down to pH 4.0. A number of investigators have described bacteria, associated with the roots ofnonleguminous plants, which fix nitrogen. Beijerinckia species have been isolated from the roots of sugar cane and several tropical grasses (7), Azotobacter paspali has been isolated from Paspalum notatum (8), Pseudomonas sp. has been found in rice (1) and in Pennisetum americanum (14), and Azospirillum species have been isolated from a variety of forage grasses, grain crops, and legumes (9, 10). In Oregon and Nebraska, Bacil

Root colonization by symplasmata-forming Enterobacter agglomerans

“…The presence of E. agglomerans in the rhizosphere of different grasses has been well documented [7, [14][15][16]. Reported densities are usually very low, but the authors have mostly used cfu measurements on macerated roots without checking the type of colonization.…”

Humus bacteria of Norway spruce stands: plant growth promoting properties and birch, red fescue and alder colonizing capacity

“…Humus suspension (20% w/v in PBS) was plated as serial dilutions on three replicate plates on Luria-Bertani [15], King's B [15], Malate [2], and Actinomycete isolation agar (Difco) with cycloheximide (75 mg l 31 ). Colony forming units were counted after 5 days incubation at 28³C.…”

“…Nitrogen-¢xing activity was scored from 0.2 ml of the humus and root suspensions (two replicates) in 22-ml serum bottles with 5 ml of N-free semisolid Malate medium [16] supplemented with 0.5% (w/v) glucose after 7 days incubation at 28³C. The acetylene reduction assay was performed as described in [2]. Serial dilutions from the positive bottles were plated on Luria agar and on Malate agar, prepared to pure cultures and tested for acetylene reduction.…”

“…Bacteria in the rhizosphere and rhizoplane of grasses and crop plants (e.g. [2,3]) have been investigated but few studies have focused on root surface bacteria of forest trees. Interactions with the host by rhizosphere bacteria of Scots pine (Pinus sylvestris) were studied by Timonen et al [4] and of Pinus radiata by Garbaye and Bowen [5], with a hybrid spruce host (Picea glaucaUengelmannii) by Chanway et al [6], and with Douglas ¢r (Pseudotsuga menziesii) by Axelrood et al [7].…”

Purification and partial characterization of an outer membrane protein involved in the adhesion of Rahnella aquatilis to wheat roots

“…Several populations of nitrogen-fixing bacteria associated with cereal roots belong to the Enterobacte-riaceae: Enterobacter agglomerans [I], E. cloacae and Klebsiella planticola [2], K. pneumoniae [3], Pantoea agglomerans [4] and Rahnella aquatilis [S]. However, very little is known about the mechanisms involved in the adhesion of these species to plant roots.…”