Chromosome map and distribution of nif genes in P . sabinae T27. A. Chromosome map. (From the outer to the inner concentric circle) Circles 1 and 2 are genes encoded by leading and lagging strands, respectively. Coding sequences are color-coded by COG categories. Circle 3 and 4 are distribution of tRNA (black) genes and rRNA (red) genes in the + strand and – strand, respectively. Circle 5 and 6 show G + C content and GC skew (G-C/G + C), respectively. The positions of nif genes and nif clusters are indicated in the chromosome map. B. The organization of nif genes. C. The organization of nif-like genes.