6 Analyzing the Functional Diversity of Plant GrowthPromoting Bacteria: Study Cases
Griffiths et al. (2000, 2001) and Wertz et al. (2006) noted that several studies indicate
that the functional redundancy of microbial communities, in general, is high and that
microbial diversity may be substantially eroded without affecting ecosystem functions. The importance of biodiversity for ecosystem functioning has been much
debated, and some contrasting results have been reported. The final and general
agreement showed that “it is not biodiversity per se that is important, but rather the
prevalence of individual species or functional groups” (Cederlund et al. 2008).
Shukla et al. (2004), Boruvka et al. (2005), Guiffre et al. (2006), and Sharma et al.
(2011a) reported that multivariate analysis including principal component analysis
(PCA) and cluster analysis could be a useful tool to select effective PGPB and has
been employed in crop yield prediction, agricultural soils, and under contrasting
management systems, to identify the origin of potentially toxic elements in ecosystems and to develop operationally important quality ecosystem indicators for longterm sustainability. The authors noted that multivariate analysis takes into consideration the whole data set instead of individual variables, thereby taking into account
several factors simultaneously; particularly, PCA is an effective data reduction
analysis that helps to explain most of the variances in a multivariate data, reducing
the number of variables into a few uncorrelated components. Subsequently, the
employ of cluster analysis allows the confirmation of PCA data, grouping the
individual inoculants and variables, allowing the understanding and characterization
of the nature of each cluster, and, finally, giving a profile that relates to the
occurrence of specific clusters to auxiliary data not used in the original analysis.
There are some particular studies regarding this kind of PGPB functional diversity analysis; Naik et al. (2008) studied the genetic and functional diversity of
phosphate-solubilizing fluorescent pseudomonads associated with rhizospheric
soils of rice and banana by an array of in vitro assays and gene amplification
technique. Since strains of fluorescent pseudomonad bacteria have also been
reported for biodegradation of agricultural pollutants (Bano and Musarrat 2003;
Naik and Sakthrivel 2006), as well as for weed control in agricultural fields (Kremer
et al. 1990; Charudattan 1991), these bacteria have been considered as an important
bioinoculants due to their innate potential to produce plant growth-promoting
hormones and enzymes (O’Sullivan and O’Hara 1992; Cattelan et al. 1999; Glick
et al. 1995; Ramamoorthy et al. 2001; Sunishkumar et al. 2005). Bacteria belonging
to the genera Mesorhizobium, Rhizobium, Klebsiella, Acinetobacter, Enterobacter,
Erwinia, Achromobacter, Micrococcus, Aerobacter, and Bacillus have been
reported as phosphate solubilizers, and strains belonging to pseudomonads are also
noted as efficient phosphate solubilizers (Villegas and Fortin 2001). Considering the
multiple applications of phosphate-solubilizing fluorescent pseudomonads, it is
essential to study their diversity, which is useful in the design of strategies to the
employ of native strains as bioinoculants.
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A. L. Guerrero-Zúñiga et al.
Griffiths et al. (2000, 2001) and Wertz et al. (2006) noted that several studies indicate
that the functional redundancy of microbial communities, in general, is high and that
microbial diversity may be substantially eroded without affecting ecosystem functions. The importance of biodiversity for ecosystem functioning has been much
debated, and some contrasting results have been reported. The final and general
agreement showed that “it is not biodiversity per se that is important, but rather the
prevalence of individual species or functional groups” (Cederlund et al. 2008).
Shukla et al. (2004), Boruvka et al. (2005), Guiffre et al. (2006), and Sharma et al.
(2011a) reported that multivariate analysis including principal component analysis
(PCA) and cluster analysis could be a useful tool to select effective PGPB and has
been employed in crop yield prediction, agricultural soils, and under contrasting
management systems, to identify the origin of potentially toxic elements in ecosystems and to develop operationally important quality ecosystem indicators for longterm sustainability. The authors noted that multivariate analysis takes into consideration the whole data set instead of individual variables, thereby taking into account
several factors simultaneously; particularly, PCA is an effective data reduction
analysis that helps to explain most of the variances in a multivariate data, reducing
the number of variables into a few uncorrelated components. Subsequently, the
employ of cluster analysis allows the confirmation of PCA data, grouping the
individual inoculants and variables, allowing the understanding and characterization
of the nature of each cluster, and, finally, giving a profile that relates to the
occurrence of specific clusters to auxiliary data not used in the original analysis.
There are some particular studies regarding this kind of PGPB functional diversity analysis; Naik et al. (2008) studied the genetic and functional diversity of
phosphate-solubilizing fluorescent pseudomonads associated with rhizospheric
soils of rice and banana by an array of in vitro assays and gene amplification
technique. Since strains of fluorescent pseudomonad bacteria have also been
reported for biodegradation of agricultural pollutants (Bano and Musarrat 2003;
Naik and Sakthrivel 2006), as well as for weed control in agricultural fields (Kremer
et al. 1990; Charudattan 1991), these bacteria have been considered as an important
bioinoculants due to their innate potential to produce plant growth-promoting
hormones and enzymes (O’Sullivan and O’Hara 1992; Cattelan et al. 1999; Glick
et al. 1995; Ramamoorthy et al. 2001; Sunishkumar et al. 2005). Bacteria belonging
to the genera Mesorhizobium, Rhizobium, Klebsiella, Acinetobacter, Enterobacter,
Erwinia, Achromobacter, Micrococcus, Aerobacter, and Bacillus have been
reported as phosphate solubilizers, and strains belonging to pseudomonads are also
noted as efficient phosphate solubilizers (Villegas and Fortin 2001). Considering the
multiple applications of phosphate-solubilizing fluorescent pseudomonads, it is
essential to study their diversity, which is useful in the design of strategies to the
employ of native strains as bioinoculants.
242
A. L. Guerrero-Zúñiga et al.