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Efficiency of nitrogen fixation by lysogenic and non-lysogenic isolates of Rhizobium nodulated Sesbania aegyptica.

Omnia Sobhy Mohamed Hashem.

Abstract
Six Sesbania nodulating rhizobia designated as (RS1, RS2, RS3, RS4, RS5 and RS6) were isolated and characterized from El-Garbia and El- Menoufia governorates. These isolates were fast growing Rhizobium and produced Indole acetic acid with different concentration. Furthermore, all these isolates were varied in their response to different concentration of NaCl and Intrinsic antibiotic resistance pattern. Lysogenicity in the isolated Sesbania nodulating rhizobia was tested. One lysogenic isolate RS2 (RSL) was identified among the tested six Sesbania Rhizobium, this isolate produced turbid plaques. Single plaques was picked and propagated and designated as (ϕB5). Electron microscopy results suggested that ϕB5 belong to family Myoviridae having icosahedral head (65.27±5.09mm), long contractile tail (91.4±1.3, 17.93±1.25mm) and neck (21.0±1.3, 4.2±0.0) and has approximately 23.5Kpb of dsDNA. Further incubation time of lytic area performed by plating of RSL with ϕB5 lead to appearance of resistance Rhizobium colony (RP5). This purified colony was non-lysogenic Rhizobium. The symbiotic interaction of RSL (phage sensitive) and RP5 (phage resistance) was studied using Sesbania aegyptica as a host in presence and absence of phages. Assay of symbiotic efficiency based on nodule number, nitrogenase activity, dry weight and total nitrogen of shoot system was detected. Symbiotic effectiveness in phage resistance non-lysogenic isolate was higher than in lysogenic phage sensitive isolate in presence of phages in soil. Our study showed a significant relationship between the phage sensitivity and symbiotic efficiency of the isolated Rhizobium.

Key words: nitrogen fixation;lysogenic and non-lysogenic isolates;Rhizobium nodulated Sesbania aegyptica


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