Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

60j 4 A Review on the Taxonomy and Possible Screening Traits of Plant Growth Promoting Rhizobacteria
Figure 4.1 Taxonomic resolution of some of
the currently used techniques in taxonomy
(from Vandamme et al. [29]). Phage and bacteriocin
typing, serological (monoclonal, polyclonal)
techniques and genomic studies such
as restriction fragment length polymorphism
(RFLP) and low-frequency restriction fragment
analysis (PFGE); 2: Zymograms (multilocus
enzyme polymorphism), total cellular protein
electrophoretic patterns and genomic techni-
ques such as ribotyping, DNA amplification
(AFLP, AP-PCR, rep-PCR, RAPD, etc.); 3: Genomic
techniques such as DNA–DNA hybridization,
mol% G + C, DNA amplification
(ARDRA) and tDNA-PCR; 4: Chemotaxonomic
markers (polyamines, quinones, etc.); 5: Cellular
fatty acid fingerprinting (FAME); 6: Cell
wall structure; 7: Phenotype (classical, API,
Biolog, etc.); 7: rRNA sequencing; 8, DNA
probes and DNA sequencing.
An effective polyphasic taxonomy will encompass the study of different molecule
types within the bacterial cell, for instance membrane fatty acids, proteins, ribosomes/ribosomal
gene sequences and other biochemical and phenotypic characteristics
that will produce a robust characterization of the strains and achieve a sound
classification system in order to obtain the most reliable strain identifications. A
good review on the modern polyphasic bacterial taxonomy is offered by Zakhia and
de Lajudie [7] (Figure 4.1).
The phenotypic techniques used nowadays embrace morphological, physiological
and biochemical characteristics of the strains studied using classical methodologies
or commercialized systems, plus analyses of cellular components such
as cellular fatty acids by the fatty acid methyl ester (FAME) technique, evaluation
of total cellular proteins by the sodium dodecyl sulfate-polyacrylamide gel electrophoresis
(SDS-PAGE) technique and multilocus enzyme electrophoresis
(MLEE).
This work intends to give the reader an insight into the present taxonomical status
of the main groups of PGPR, as reviewed in Table 4.2. In later sections, symbiotic
and asymbiotic plant growth promoting bacteria are described according to their
taxonomic positions.