Isolation and characterization of a bacteriocin produced by Cicer-Rhizobium

A constitutively expressed bacteriocin from Cicer-Rhizobium was purified to homogeneity. The purified preparation yielded a homogenous protein with a molecular weight of about 29 kDa. This protein was heat stable, unaffected by nucleases and was found to have an iso-electric point (pI) of 4.6. The N-terminal sequence of the protein was found to be M-N-N-N-Y-R-E-L-L-P-I-I-G-P-P-W-A-E-I-E, sharing 78% homology with linocin M18. Bacteriocin bioactivity was correlated with the presence of a 29 kDa protein in the growth diffusates of the culture. A mutant strain unable to produce this bacteriocin was found to have a statistically significant reduction in nodule occupancy and competitiveness against the wild type and indigeneous populations under unsterile conditions. Bacteriocin production by the mutant carrying the complement clone pJNP365 was found to be stable even in an unsterile environment.