Physiological and Molecular Assessment of Sesbania Root Nodules Bacteria from Different Iraqi Areas for Salt Tolerance

Abstract

Thirty two isolates of aerobic gram-negative bacteria associated with Sesbania sesban grown in different saline Iraqi soils was identified according to morphological and physiological characteristics, cultured on yeast-mannitol agar medium (YEMA) supplemented with different NaCl concentrations. It was indicated that 53.12% of isolates were highly tolerant to salinity, tolerated from 4.0 to 5.0 w/v NaCl. All thirty two Rhizobia isolates performed positive strong reaction to Catalase enzyme except for three were negative to this enzyme. Concerning exo-polysaccharide (EPS) production the isolates displayed a significant difference between them and that salt tolerance isolates gave a high amount of EPS production in compare to the sensitive ones. As for antibiotic sensitivity of Sesbania isolates data revealed that 83% of isolates were highly resistant to Ampicilin at 50 µgml-1, the cluster analysis based on all phenotypical and physiological characters divided the isolates into two major groups, the first group included one isolate Ses10, which was salt moderate tolerant. The second group included the rest of isolates which splits into two subgroups with 6% similarity, the first subgroup comprised all sensitive isolates plus one salt moderate tolerant isolate (Ses9).The assumption that district environmental conditions plays a vital role on field survival of bacteria, give rise to the use of PCR methods to identify Rhizobia. In this study the genetic divergence of fast nodulating bacteria connected with Sesbania in Iraq was examined. A selection of Rhizobia isolates were characterized by RAPD –PCR. Amplification of genomic DNA using three random primers (RAPD) gave various bands, the results revealed that most efficient and highest discrimintory power primer was 35.4% and 37% respectively for primer OPA-10. The cluster analysis based on RAPD-PCR amplification results showed two divergent groups with 15% similarity, the first group included two salt sensitive Ses17 and Ses28, and the second major group comprised all salt moderate and tolerant isolates.