Isolation of Acetylene-reducing Spirilla from the Roots of Potamogeton filiformis from Loch Leven (Kinross)

Abstract

I N T R O D U C T I O NSignificant levels of nitrogen-fixation, measured using 15N2, and/or acetylene reduction (Hardy et al., 1968), occur on the roots of non-leguminous aquatic macrophytes (Patriquin & Knowles, 1972;Bristow, 1974), and on the roots of rice seedlings growing in waterlogged soil (Dommergues et al., 1973). This activity is attributed to asymbiotic bacteria. Microaerophilic acetylene-reducing spirilla have been isolated from the roots of maize (von Bulow & Dobereiner, 1975) and Digitaria decumbens (Day & Dobereiner, 1976) plants in Brazil; these roots also showed high levels of nitrogenase activity by the acetylene-reduction method. The root zone of some aquatic macrophytes is known to be aerated via a channel of tissue (aerenchyma) through which air passes from the shoots to the roots (Armstrong, 1972). This enables the plants to grow in anaerobic sediment. The aerobic or semi-aerobic zone immediately around the roots is likely to be suitable for microaerophilic bacteria. In this study the roots of Potamogeton Jiliformis, one of the major aquatic macrophytes in Loch Leven, Kinross, Scotland (Jupp, Spence & Britton, 1974), were examined for the presence of nitrogen-fixing spirilla, and some characteristics of pure cultures of the organisms isolated from them were investigated. M E T H O D SBasic medium. This contained: 0.4 g KH,PO,; 0.1 g K,HPO,; 0.2 g MgSO,. 7H,O; 0 -1 g NaCl; 0-02 g CaCl,; 0.01 g FeCI,; 0.002 g NaMoO,.zH,O; 3.5 g (semi-solid) or 15 g (pour plates) Difco Bacto Special Noble Agar; I 1 distilled water. The carbon and nitrogen sources added to this medium in different experiments are described below. All incubations were at 30 "C.Preliminary enrichment cultures. Samples of P. $Ziformis roots (0.5 to 1.0 cm long) were taken and, on the same day, were washed in lake water and placed in semi-solid medium (I cm deep in I oz vials) containing 0.5 % sodium malate. After incubation for I day, the root pieces were removed and acetylene-reduction tests were carried out on the cultures.Purification. Purification of acetylene-reducing cultures as described by von Bulow & Dobereiner (I 975) was not successful. Purification was achieved by mixing samples from preliminary enrichment cultures which reduced the most acetylene with 5 ml sterile distilled water or buffered saline (pH 7.0) for 5 min; and then inoculating 0.1 ml samples into pour plates containing 0.5 % sodium malate and 0.05 % yeast extract, and incubating for 7 days.

Isolation of a nitrogen-fixing Campylobacter species from the roots of Spartina alterniflora Loisel

“…Nitrogenase activity is associated with many nonnodulated angiosperms growing in both upland (e.g., Dobereiner et al 1972;Day et al 1975;Nelson et al 1976; Smith and Patriquin 1978) and lowland or aquatic habitats (e.g., Bristow 1974; Patriquin and Keddy 1978;Sylvester-Bradley 1976; Yoshida andAncajas 1971, 1973). Nitrogen-fixing bacteria of the genus Azospirillutn (syn.…”