Diversity and Environmental Stress Responses of Rhizobial Bacteria from Egyptian Grain Legumes

Abstract

The aim of this work was to characterize and identify root-nodule bacteria isolated from different grain leguminous plants grow in the cultivated lands of Beni-Suef Governorate, Egypt. The bacteria (68 isolates) were obtained from five cultivated grain leguminous plants, namely: Cicer arietinum, Lens esculentus, Phaseolus vulgaris, Pisum sativum, and Vicia faba, and one naturally- grown herb legume, Trifolium resupinatum. After their isolation, the bacteria were confirmed as rhizobia by re-nodulating their specific host legumes. The phenotypic characteristics (e.g. utilization of carbon and nitrogen sources, tolerance to salt, acid, heat, and heavy metals, antibiotic resistance, etc.) were determined. The bacteria under investigation expressed noticeable ability to grow under various stress factors examined. These rhizobial isolates could be a good candidate to establish a successful symbioses with their compatible legumes under the environmental conditions prevail in Egypt. The bacterial features of the isolates were compared to those of strains from two reference rhizobial genera (Rhizobium and Mesorhizobium). Based on phenotypic characteristics and nodulation capacity, the rhizobia were grouped and classified as the following: V. faba bacteria as R. leguminosarum and P. sativuma bacteria as R. leguminosarum and R. etli. P. vulgaris bacteria were classified as R. lusitanum, R. mongolense, and R. leguminosarum. L. esculentus bacteria were classified as R. leguminosarum and C. arietinum bacteria as M. amorphae, M. temperatum and M. mediterraneum. The bacteria of the wild-legume, T. resupinatum were classified as Ensifer meliloti and R. leguminosarum. The results emphasized the fact that the cultivated legumes nodulate by the common and diverse root-nodule bacteria (rhizobia) indigenous in the Egyptian soil. However, a molecular and genetic identification is needed to precisely classify and identify these bacteria.