Isolation and screening of native ACC deaminase and siderophore producing rhizobia

Rhizobia are bacteria that have a symbiosis with legumes. Rhizobia that have some capabilities like ACC deaminase and siderophore production in addition to nitrogen fixation are successful competitors in different environmental conditions for production of more nodules. The aim of this study was the screening of ACC deaminase and siderophore producing Rhizobia.
For screening of ACC deaminase producing rhizobia, all isolates were cultured on M9 medium with two different nitrogen sources, ACC and NH4Cl, and M9 medium without nitrogen source was considered as a control treatment. ACC deaminase producing Rhizobia were identified based on statistical comparison of growth rate on M9 medium with ACC against other mediums. Chrome Azurol S (CAS) liquid assay was used for siderophore producing Rhizobia. All treatments repeated two times and all data analyzed in the base of the completely randomized design. 16S rRNA gene sequencing was used for identifying the best ACC deaminase and siderophore producing strain.
14 isolates of Rhizobium were used for screening of ACC deaminase and siderophore producing isolates. Results showed that just R8 strain was isolated with the capability of ACC deaminase production. This isolate could have better growth on M9 with ACC than two other mediums. In the next experiment, it was determined that 8 isolates are siderophore producing rhizobia based on CAS liquid assay. The result showed that R12 isolate could produce more siderophore than others. According to 16S rRNA gene sequencing, R8 and R12 isolates identified as Sinorhizobium meliloti.
Discussion and The R8 strain that have the capability of ACC deaminase production probability can prevent adverse effects of ethylene during nodulation and abiotic stress. On the other side, R12 that are able to produce siderophore can prevent the growth of soil born pathogen in addition to facilitating nodulation and iron uptake by plants.