CONFORMITY AND DIVERSITY AMONG FIELD ISOLATES OF RHIZOBIUM-LEGUMINOSARUM BV-VICIAE, BV-TRIFOLII, AND BV-PHASEOLI REVEALED BY DNA HYBRIDIZATION USING CHROMOSOME AND PLASMID PROBES
G. Laguerre et al., CONFORMITY AND DIVERSITY AMONG FIELD ISOLATES OF RHIZOBIUM-LEGUMINOSARUM BV-VICIAE, BV-TRIFOLII, AND BV-PHASEOLI REVEALED BY DNA HYBRIDIZATION USING CHROMOSOME AND PLASMID PROBES, Canadian journal of microbiology, 39(4), 1993, pp. 412-419
A study was made of 113 bacterial isolates from root nodules of peas,
lentils, red clover, and French beans, which had been grown in the sam
e soil. Plasmid band profiles visualized in Eckhardt gels were analyse
d in relation to DNA hybridization patterns obtained by probing restri
cted total cellular DNA in Southern blots. Rhizobium leguminosarum chr
omosomal probes (plac12, pCOS309.1) and various symbiotic plasmid (nod
gene region) probes were used. Dominant plasmid DNA hybridization pat
terns and more frequent combinations of plasmid patterns and chromosom
al types were found among the isolates of each host plant species; the
occurrence of alternative combinations indicated that genetic transfe
r and recombination among members of this soil population had taken pl
ace. About 40% of all isolates belonged to the same chromosomal type.
Isolates of the same chromosomal type were often found with cryptic pl
asmids of the same size in different host plant species. Although isol
ates could not be assigned to their respective plant host groups using
chromosomal probes alone, this was generally possible using symbiotic
plasmid probes and the results were in complete accordance with plant
tests. However, there was a group of bean isolates in which no homolo
gy to any of the R. leguminosarum probes was detected under the condit
ions of high stringency used. Other exceptional isolates of beans conf
ormed in probe tests and subsequent plant host specificity tests bette
r to biovars viciae or trifolii than to biovar phaseoli; thus, the nod
ulation of beans (i.e., Phaseolus vulgaris) in the field appears less
subject to stringent control of specificity than that of other host pl
ant species. It was also noted that the nod gene regions probed showed
greater diversity in isolates of biovars viciae and trifolii than in
biovar phaseoli.