Azide resistance in <i>Rhizobium ciceri </i>linked with superior symbiotic nitrogen fixation

Abstract

Isolated azide resistant (Az^R) native <i>R. ciceri </i>strain 18-7 was resistant to sodium azide at 10 <i>μg</i>/ml<i>. </i>To find if <i>nif-</i>reiteration is responsible for azide resistance and linked to superior symbiotic nitrogen fixation, transposon (<i>Tn5</i>)<i> </i>induced azide sensitive mutants were generated. Using 4 kb <i>nif</i>-reiterated <i>Sinorhizobium meliloti </i>DNA, a clone C4 that

complemented azide sensitivity was isolated by DNA hybridization from genomic library of chickpea <i>Rhizobium </i>strain Rcd30 l. <i>Eco</i>RI<i> </i>restriction mapping revealed the presence of 7 recognition sites with a total insert size of 19.17 kb. Restriction analysis of C4 clone and <i>nif</i>-reiterated DNA (pRK 290.7) with <i>Eco</i>RI<i> </i>and <i>Xho</i>I<i> </i>revealed similar banding pattern. Wild type strain 18-7, mutant M126 and complemented mutant M126(C4) were characterized for symbiotic properties (<i>viz.,</i>acetylene reduction assay, total nitrogen content, nodule number and fresh and dry weight of the infected plants) and <i>explanta </i>nitrogenase activity. Our results suggested that azide resistance, <i>nif</i>-reiteration , and superior symbiotic effectiveness<i> </i>were interlinked with no correlation between <i>ex-planta </i>nitrogenase activity and azide resistance in <i>R. ciceri.</i>