PRODUCTION Of NUTRIENT SOURCES FOR RHIZOBIUM

available (Burton, 1965). The molecular biology techniques, the new technique for study genotypic
and phylogeny of rhizobia also has been developing from time to time.
Eventually, with the development of molecular sequencing technique especially of the 16S
rRNA gene, the situation has changed. The most prominent person in initiating this revolution study
of microbial phylogeny and evolution was Carl Woese who from the sixties on has relentlessly
worked towards defining the natural order of microbial life (Woese 1987; Woese 1994; Morell 1997).
The current status of rhizobial taxonomy as shown in table 1, a few years after the work of
Young et al. (1996), the first phylogenetic trees based on close to full-length 16S sequences were
published for rhizobia and related organishs (Willems and Collins, 1993; Yanagi and Yamasato,
1993). These trees showed that rhizobia can be devided into three clusters: 1) the fast-or moderategrowing
rhizobia in the genera Rhizobium, Sinorhizobium, Mesorhizobium, and R.galegae, which is
located in the branch containing serveral Agrobacterium species, 2) the slow-growing Bradyrhizobium
and 3) the stem nodulating Azorhizobium. Sequencing of the full length of the 16S rRNA gene is now
required for the description of new species. The correlation between full-length sequences and various
shorter fragments has in general proved to be good and very useful when used for initial strain
recognition and screening of large numbers of isolates (Oyaizu et al., 1993; Laguerre et al., 1993; So
et al., 1994; van Rossum et al., 1995; Hernandez-Lucas et al., 1995; Urtz and Elkan, 1996).
Table 1. Currently described species of rhizobia.
Rhizobium species Representative strains
Rhizobium
Rhizobium leguminosarum ATCC 10004
bv. viciae, trifolii and phaseoli
Rhizobium tropici type B CIAT 899
type A CFN 299
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