Abstract
The investigation was carried out to study the characteristics of rhizobial strains isolated from the leguminous plant, Sesbania bispinosa growing in different regions of Bangladesh. Forty-four isolates were studied for biochemical and molecular characteristics. Isolates were able to utilize different carbohydrates. All isolates showed complete resistance to cloxacillin and penicillin G that results in increased survivability of rhizobial populations in antibiotic stressed conditions. Isolates were able to form nodule in the plant infection test. The majority of the strains showed positive results for nodC and nifH gene amplification which are the typical characteristics of Rhizobium species. Genetic relatedness was assessed by comparing the sequences of 16S rRNA. Two distinct clusters were seen in the dendrogram constructed by the Complete Linkage method. The isolates R7, R8, R17, R33 and R3 were distinct from the 20 reference strains. The first cluster was phylogenetically distinct from the reference strains and might have evolved from a distinct lineage. Isolate R4 was placed adjacent to Rhizobium cnuense. So, the findings may represent new species of Rhizobium. This study helps to identify an ideal strain of Rhizobium from S. bispinosa that can be function as biofertilizer when released in the soil and contribute to sustainable agricultural practices by improving yields. Key words: Rhizobium, Sesbania bispinosa, nodulation gene, nitrogen fixation gene, sequencing.
Highlights
Nitrogen is one of the most abundant nutrient supplement for plant growth and is not directly available to plants because of its strong triple covalent bond
The investigation was carried out to study the characteristics of rhizobial strains isolated from the leguminous plant, Sesbania bispinosa growing in different regions of Bangladesh
For the amplification of the 16S rRNA gene, the polymerase chain reaction (PCR) contents were subjected to initial denaturation at 94°C for 5 min followed by 30 cycles of denaturation at 94°C for 45 s
Summary
Nitrogen is one of the most abundant nutrient supplement for plant growth and is not directly available to plants because of its strong triple covalent bond. Rhizobia form nodules on root to fix nitrogen where nod factor and flavonoids initiate nodulation (Oldroyd, 2013). Mulligan et al (1985) demonstrated that nodulation genes, the regulatory genes, and the nitrogen fixing genes are located on large symbiotic plasmid. Antibiotics accumulation in soils after excretion from feces and urine was reported by Ji et al (2012). These antibiotics are lethal to susceptible rhizobial population and decreased rhizobial persistence in the soil and total nitrogen fixation. Cole et al (1973) and Frioni et al (2001) reported that greatest difference of antibiotics tolerance was found between fast and slow growing rhizobia. Molecular methods including polymerase chain reaction (PCR) and 16S rRNA sequencing are more reliable for identification of bacterial isolates
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