6 Microbial Endophytes: New Direction to Natural Sources
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et al. 2020). In the endophytic relationship, microbes provide a unique opportunity
indirectly for control of the deleterious impact of phytopathogens on health of plant
and soil, via synthesis of innumerable compounds, for example, antibiotics, immunesuppressants, biocontrol agents, hydrogen cyanide (HCN), and ammonia, induced
systemic tolerance, production of hydrolytic enzymes (Yadav et al. 2017). In addition, few endophytic bacteria are also used in genetic engineering to transfer specific
genes to the host plant (Tomasino et al. 1995). Endophytic microbes can maintain
sustainable agriculture, i.e., enhanced the health, yield, productivity of plants via
numerous independent or linked mechanisms. There are many reports on isolation
of endophytic bacteria from roots, stems, leaves, seeds, needles, twigs, and barks of
different plant species and their agricultural applications (Yadav et al. 2020).
Nitrogen-fixing endophytes make up a small portion of the total population of
endophytes and they are mainly considered for nitrogen fixation. Nitrogen-fixing
endophytes have been found in seed and root of some rice cultivars (Mano and
Morisaki 2008). Recently, more focus is laid on the isolation and identification of
nitrogen-fixing endophytic bacteria in cereal crops (Verma et al. 2015, 2019).
6.6 Biodiversity of Bacterial Endophytes
Previous reviews have described the diversity of bacterial endophytes in multiple
plant species, especially those with agronomical interest (Rosenblueth and MartínezRomero 2006). More recently, Romero et al. (2014) demonstrated the power of
the 16S-rRNA pyrosequencing approach in determining the position of endophytic bacterial communities in tomato. The endophyte communities were mainly
comprised of five phyla, with Proteobacteria as the most highly represented as
90%. Other phyla detected were actinobacteria by 1.5%, Planctomycetes 1.4%,
Verrucomicrobia 1.1%, and Actinobacteria is only about 0.5%.
In addition, the dynamics of endophytic bacterial communities of sugar beet
(Beta vulgaris L.) with different plant genotypes and plant growth stage changes
was recently analyzed by PCR-based llumina pyrosequencing (Shi et al. 2014).
The most abundant division was the Proteobacteria, with 98% of the total microbial endophyte community being composed of Enterobacteriales, Pseudomonadales,
Xanthomonadales, Rhizobiales, Sphingomonadales, Burkholderiales, Actinomycetales, and flavobacteriales. In general, the Phylum Proteobacteria, including the
classes α, β, and γ -Proteobacteria, are reported to be dominant in diversity analysis of endophytes. Although, members of the Firmicutes and Actinobacteria are
also among this classes as most consistently found as endophytes. Other classes
such as Bacteroidetes, Planctomycetes, Verrucomicrobia, and Acidobacteria are less
commonly found as endophytes.
The most commonly found genera of bacterial endophytes are Pseudomonas,
Bacillus, Burkholderia, Stenotrophomonas, Micrococcus, Pantoea, and Microbacterium (Romero et al. 2014; Rosenblueth and Martínez-Romero 2006; MarquezSantacruz et al. 2010; Shi et al. 2014). All these genera, described as bacterial
133
et al. 2020). In the endophytic relationship, microbes provide a unique opportunity
indirectly for control of the deleterious impact of phytopathogens on health of plant
and soil, via synthesis of innumerable compounds, for example, antibiotics, immunesuppressants, biocontrol agents, hydrogen cyanide (HCN), and ammonia, induced
systemic tolerance, production of hydrolytic enzymes (Yadav et al. 2017). In addition, few endophytic bacteria are also used in genetic engineering to transfer specific
genes to the host plant (Tomasino et al. 1995). Endophytic microbes can maintain
sustainable agriculture, i.e., enhanced the health, yield, productivity of plants via
numerous independent or linked mechanisms. There are many reports on isolation
of endophytic bacteria from roots, stems, leaves, seeds, needles, twigs, and barks of
different plant species and their agricultural applications (Yadav et al. 2020).
Nitrogen-fixing endophytes make up a small portion of the total population of
endophytes and they are mainly considered for nitrogen fixation. Nitrogen-fixing
endophytes have been found in seed and root of some rice cultivars (Mano and
Morisaki 2008). Recently, more focus is laid on the isolation and identification of
nitrogen-fixing endophytic bacteria in cereal crops (Verma et al. 2015, 2019).
6.6 Biodiversity of Bacterial Endophytes
Previous reviews have described the diversity of bacterial endophytes in multiple
plant species, especially those with agronomical interest (Rosenblueth and MartínezRomero 2006). More recently, Romero et al. (2014) demonstrated the power of
the 16S-rRNA pyrosequencing approach in determining the position of endophytic bacterial communities in tomato. The endophyte communities were mainly
comprised of five phyla, with Proteobacteria as the most highly represented as
90%. Other phyla detected were actinobacteria by 1.5%, Planctomycetes 1.4%,
Verrucomicrobia 1.1%, and Actinobacteria is only about 0.5%.
In addition, the dynamics of endophytic bacterial communities of sugar beet
(Beta vulgaris L.) with different plant genotypes and plant growth stage changes
was recently analyzed by PCR-based llumina pyrosequencing (Shi et al. 2014).
The most abundant division was the Proteobacteria, with 98% of the total microbial endophyte community being composed of Enterobacteriales, Pseudomonadales,
Xanthomonadales, Rhizobiales, Sphingomonadales, Burkholderiales, Actinomycetales, and flavobacteriales. In general, the Phylum Proteobacteria, including the
classes α, β, and γ -Proteobacteria, are reported to be dominant in diversity analysis of endophytes. Although, members of the Firmicutes and Actinobacteria are
also among this classes as most consistently found as endophytes. Other classes
such as Bacteroidetes, Planctomycetes, Verrucomicrobia, and Acidobacteria are less
commonly found as endophytes.
The most commonly found genera of bacterial endophytes are Pseudomonas,
Bacillus, Burkholderia, Stenotrophomonas, Micrococcus, Pantoea, and Microbacterium (Romero et al. 2014; Rosenblueth and Martínez-Romero 2006; MarquezSantacruz et al. 2010; Shi et al. 2014). All these genera, described as bacterial