methods in biochemical-based techniques and molecular-based techniques and
mention that typically, diversity studies consider the relative diversities of communities across a gradient of stress, disturbance, or other biotic or abiotic difference.
Atlas and Bartha (1993) noted that the information gathered by diversity studies are
finally reduced to discrete numerical measurements defined as diversity indices.
5 Plant Growth-Promoting-Bacteria: Functional Attributes
Actually, PGPB’s traits are those that include knowing functional activities: the
ability to produce or change the concentration of plant hormones (Mahmoud et al.
1984; Frankenberger and Arshad 1995; Glick 1995; Garcia de Salamon et al. 2001;
Ahmad et al. 2008); N 2 fixation (Zaidi 1999; Wani et al. 2007a); antagonism against
phytopathogenic microorganisms by production of siderophores, b-1,3-glucanase,
chitinases, antibiotics, and cyanide (Renwick et al. 1991; Shanahan et al. 1992;
Flaishman et al. 1996; Khan et al. 2002; Wani et al. 2007a, b); and solubilization of
inorganic phosphates and toxic metals (Wani et al. 2007b, c).
Becerra-Castro et al. (2012) and Cabello-Conejo et al. (2014) established that the
screening methods employ inert growth substrates that allow a rapid selection of
interesting strains and after they could be tested in more complex systems, where
bacterial mechanisms should be freely induced.
Ullah et al. (2015) mention that it is important to note that not only works about
PGPB’s functional diversity precise mode of action; ecophysiology and promising
potential bioinoculants for maintaining soil fertility and the sustainability of crops in
diverse agroecosystems are also important to determine if these microorganisms
possess the ability to affect heavy metal mobility and availability to the plant through
the release of chelating agents, acidification, phosphate solubilization, and redox
changes as Yan-de et al. (2007) and Gadd (2004, 2005, 2010) established. There
have been a large number of studies (Lebeau et al. 2008; Kidd et al. 2009; Glick
2010, 2014; Becerra-Castro et al. 2013; Sessitsch et al. 2013; Muehe et al. 2015)
indicating that plant-associated microorganisms are indeed essential players in metal
phytoextraction or phytomining, enhancing the plants’ growth and health by the
increase of nutrient uptake and improving their resistance to pathogens and stress
(Göhre and Paszkowski 2006; Lebeau et al. 2008; Lugtenberg and Kamilova 2009).
It is known that most of phosphate-solubilizing bacteria and siderophore producers,
bacteria with ACC deaminase activity and phytohormone producers, improve
plants’ growth and transform heavy metals into soluble and bioavailable forms,
favoring that plants take up contaminants (Ullah et al. 2015). Thus, these kinds of
bacteria can assist in the phytoremediation of heavy metals, either directly or
indirectly: directly involving the solubilization and removal of them from solid
matrices, such as soil, dumps, sediments, and other industrial and municipal wastes,
giving more bioavailability and final accumulation by plants, and indirectly, by the
improvement of plants’ growth to prevent the effect of phytopathogens, facilitating
the accumulation of heavy metals (Gadd 2004; Yan-de et al. 2007; Glick 2010).
10 Functional Diversity of Plant Endophytes and Their Role in Assisted. . .
241
mention that typically, diversity studies consider the relative diversities of communities across a gradient of stress, disturbance, or other biotic or abiotic difference.
Atlas and Bartha (1993) noted that the information gathered by diversity studies are
finally reduced to discrete numerical measurements defined as diversity indices.
5 Plant Growth-Promoting-Bacteria: Functional Attributes
Actually, PGPB’s traits are those that include knowing functional activities: the
ability to produce or change the concentration of plant hormones (Mahmoud et al.
1984; Frankenberger and Arshad 1995; Glick 1995; Garcia de Salamon et al. 2001;
Ahmad et al. 2008); N 2 fixation (Zaidi 1999; Wani et al. 2007a); antagonism against
phytopathogenic microorganisms by production of siderophores, b-1,3-glucanase,
chitinases, antibiotics, and cyanide (Renwick et al. 1991; Shanahan et al. 1992;
Flaishman et al. 1996; Khan et al. 2002; Wani et al. 2007a, b); and solubilization of
inorganic phosphates and toxic metals (Wani et al. 2007b, c).
Becerra-Castro et al. (2012) and Cabello-Conejo et al. (2014) established that the
screening methods employ inert growth substrates that allow a rapid selection of
interesting strains and after they could be tested in more complex systems, where
bacterial mechanisms should be freely induced.
Ullah et al. (2015) mention that it is important to note that not only works about
PGPB’s functional diversity precise mode of action; ecophysiology and promising
potential bioinoculants for maintaining soil fertility and the sustainability of crops in
diverse agroecosystems are also important to determine if these microorganisms
possess the ability to affect heavy metal mobility and availability to the plant through
the release of chelating agents, acidification, phosphate solubilization, and redox
changes as Yan-de et al. (2007) and Gadd (2004, 2005, 2010) established. There
have been a large number of studies (Lebeau et al. 2008; Kidd et al. 2009; Glick
2010, 2014; Becerra-Castro et al. 2013; Sessitsch et al. 2013; Muehe et al. 2015)
indicating that plant-associated microorganisms are indeed essential players in metal
phytoextraction or phytomining, enhancing the plants’ growth and health by the
increase of nutrient uptake and improving their resistance to pathogens and stress
(Göhre and Paszkowski 2006; Lebeau et al. 2008; Lugtenberg and Kamilova 2009).
It is known that most of phosphate-solubilizing bacteria and siderophore producers,
bacteria with ACC deaminase activity and phytohormone producers, improve
plants’ growth and transform heavy metals into soluble and bioavailable forms,
favoring that plants take up contaminants (Ullah et al. 2015). Thus, these kinds of
bacteria can assist in the phytoremediation of heavy metals, either directly or
indirectly: directly involving the solubilization and removal of them from solid
matrices, such as soil, dumps, sediments, and other industrial and municipal wastes,
giving more bioavailability and final accumulation by plants, and indirectly, by the
improvement of plants’ growth to prevent the effect of phytopathogens, facilitating
the accumulation of heavy metals (Gadd 2004; Yan-de et al. 2007; Glick 2010).
10 Functional Diversity of Plant Endophytes and Their Role in Assisted. . .
241