M. Gottfert et al., Potential symbiosis-specific genes uncovered by sequencing a 410-kilobase DNA region of the Bradyrhizobium japonicum chromosome, J BACT, 183(4), 2001, pp. 1405-1412
The physical and genetic map of the Bradyrhizobium japonicum chromosome rev
ealed that nitrogen fixation and nodulation genes are clustered. Because of
the complex interactions between the bacterium and the plant, we expected
this chromosomal sector to contain additional genes that are involved in th
e maintenance of an efficient symbiosis, Therefore, we determined the nucle
otide sequence of a 410-kb region, The overall G+C nucleotide content was 5
9.1%, Using a minimum gene length of 150 nucleotides, 388 open reading fram
es (ORFs) were selected as coding regions. Thirty-five percent of the predi
cted proteins showed similarity to proteins of rhizobia, Sixteen percent we
re similar only to proteins of other bacteria. No database match was found
for 29%, Repetitive DNA sequence-derived ORFs accounted for the rest. The s
equenced region contained all nitrogen fixation genes and, apart from nodM,
all nodulation genes that were known to exist in B, japonicum. We found se
veral genes that seem to encode transport systems for ferric citrate, molyb
date, or carbon sources. Some of them are preceded by -24/-12 promoter elem
ents. A number of putative outer membrane proteins and cell wall-modifying
enzymes as well as a type III secretion system might be involved in the int
eraction with the host.