Implication of Symbiotic Regulators on the Expression of Type VI Secretion System in Sinorhizobium fredii USDA257.

Abstract

Rhizobia are Gram negative bacteria that establish symbiosis with legumes and carry out the biological fixation of N 2 facilitating its assimilat ion by the plants , thus being considered an alternative to chemical fertilizers. Therefore, it is of great interest to understand all the mechanisms underlying this symbiosis. The Type VI Secretion System (T6SS) enable s bacteria to translocate effector protei ns to other bacteria or eukaryotic cells . T his system is present in Sinorhizobium fredii USDA257, a model organism used to study plant microbe interactions. However, its role remains practically unknown In this work we seek to discern th e regulation of this system in Sinorhizobium fredii USDA257 via studying the implic a tion of s ymbiotic regulator genes such as n odD2 , n olR , s yrM and m ucR . Furthermore , the d etermination of inducing and repressing media for this system is key to carry out further research towards a better understanding of the system. W e found that the T6SS is activated the most in Minimum Medium, compared to other culture media. In this medium, both gene expression and protein secretion of this system were activated to a high extent. Oppositely , in Tryptone Yeast medium the T6SS was in duced the least We aimed to obtain non functional gene mutants to test the effect of the regulators on the expression of the T6SS in both inducing and repressing conditions , obtaining simple recombinant mutants of syrM and mucR . We expect our assays to be a starting point for more advanced research on this topic, since the understudied T6SS is likely to have the potential of improv ing rhizobia legume symbiosis.