of rice roots by PAL5 (Meneses et al. 2011) (Table 20.2). Also, a similar deficiency
in the formation of biofilm and attachment was reported in mutants of Rhizobium
leguminosarum biovar viciae 3841 that were not able to produce EPS and
glucomannan (Williams et al. 2008; Pinski et al. 2019). In addition, cellulose is
another major component of the biofilm in some species. The study of a mutant that
lacks cellulose production (wssD gene mutation in Herbaspirillum rubrisubalbicans
M1) showed a decrease in attachment to the root surface of plants (Monteiro
et al. 2012).
The surface-associated protein LapA of Pseudomonas functions in biofilm production and contributes to cell-to-cell attachment by regulating cell hydrophobicity
(Ainelo et al. 2017). In a lapA mutant, initial attachment to the roots was similar to
that observed for the wild type, but the formation of a microcolony and the
subsequent development of a mature biofilm was impaired, resulting in poorer root
colonization (Martinez-Gil et al. 2010). Only those bacteria that can adhere to the
surface of roots will be able to colonize the inside of a plant, although root exudates
can attract both groups of bacteria. Adhesion to roots can be mediated by the
previously described flagella and pili, as well as by specialized proteins such as
curli and hemagglutinins (Kandel et al. 2017; Hardoim et al. 2015) (Table 20.2). In
Salmonella enterica, the agfA gene encodes the secreted curli protein subunit, while
afgB encodes the surface-exposed nucleator around which the curli amyloid fibers
form. The knockout mutants of the agfB gene have shown a decrease in both the
initial attachment as well as the progress of attachment and colonization over time,
whereas inactivation of the agfA gene did not influence on the initial attachment and
colonization (Barak et al. 2005). Although hemagglutinins are well known for their
role in both plant and human pathogenesis, genes encoding for hemagglutinins are
also frequently reported in the genomes of endophytic bacteria (Taghavi et al. 2010;
Miter et al. 2013; Pedrosa et al. 2011) and upregulation of two genes encoding the
filamentous hemagglutinin proteins (Hsero_1294 and fhaB) in H. seropedicae SmR1
when the mutants were attached to plant roots has suggest their involvement in
attachment to the root surface (Pankievicz et al. 2016) (Table 20.2).
In Gram-negative bacteria, lipopolysaccharide (LPS) consists of three components: (1) lipid A, (2) a core region, and (3) O-antigen. Of those three, core region
usually consists of no more than five sugar units (Steimle et al. 2016). Rhamnose is a
monosaccharide that is frequently detected as part of LPS.
The O-antigen and its biosynthesis requires four genes—rfbABCD. In general,
the genes involved in LPS biosynthesis have been reported to be upregulated during
early stages of colonization (Shidore et al. 2012; Camilios-Neto et al. 2014). The
mutation of one of the genes (in the mutation of either rfbB or rfbC) related to
rhamnose biosynthesis resulted in a 100-fold lower level of attachment to the root
surface and a lower endophytic colonization of maize (Z. mays) by H. seropedicae
SmR1 (Balsanelli et al. 2010) (Table 20.2).
The membrane protein in bacteria is also critical for the successful plant and
endophyte interactions. Of these, the muropeptide permease is necessary for peptidoglycan recycle of bacterial cell wall (Pinski et al. 2019). The sensitivity to SDS
and alterations in the LPS biosynthesis increased when the gene of this permease in
402
S.-C. Chun
in the formation of biofilm and attachment was reported in mutants of Rhizobium
leguminosarum biovar viciae 3841 that were not able to produce EPS and
glucomannan (Williams et al. 2008; Pinski et al. 2019). In addition, cellulose is
another major component of the biofilm in some species. The study of a mutant that
lacks cellulose production (wssD gene mutation in Herbaspirillum rubrisubalbicans
M1) showed a decrease in attachment to the root surface of plants (Monteiro
et al. 2012).
The surface-associated protein LapA of Pseudomonas functions in biofilm production and contributes to cell-to-cell attachment by regulating cell hydrophobicity
(Ainelo et al. 2017). In a lapA mutant, initial attachment to the roots was similar to
that observed for the wild type, but the formation of a microcolony and the
subsequent development of a mature biofilm was impaired, resulting in poorer root
colonization (Martinez-Gil et al. 2010). Only those bacteria that can adhere to the
surface of roots will be able to colonize the inside of a plant, although root exudates
can attract both groups of bacteria. Adhesion to roots can be mediated by the
previously described flagella and pili, as well as by specialized proteins such as
curli and hemagglutinins (Kandel et al. 2017; Hardoim et al. 2015) (Table 20.2). In
Salmonella enterica, the agfA gene encodes the secreted curli protein subunit, while
afgB encodes the surface-exposed nucleator around which the curli amyloid fibers
form. The knockout mutants of the agfB gene have shown a decrease in both the
initial attachment as well as the progress of attachment and colonization over time,
whereas inactivation of the agfA gene did not influence on the initial attachment and
colonization (Barak et al. 2005). Although hemagglutinins are well known for their
role in both plant and human pathogenesis, genes encoding for hemagglutinins are
also frequently reported in the genomes of endophytic bacteria (Taghavi et al. 2010;
Miter et al. 2013; Pedrosa et al. 2011) and upregulation of two genes encoding the
filamentous hemagglutinin proteins (Hsero_1294 and fhaB) in H. seropedicae SmR1
when the mutants were attached to plant roots has suggest their involvement in
attachment to the root surface (Pankievicz et al. 2016) (Table 20.2).
In Gram-negative bacteria, lipopolysaccharide (LPS) consists of three components: (1) lipid A, (2) a core region, and (3) O-antigen. Of those three, core region
usually consists of no more than five sugar units (Steimle et al. 2016). Rhamnose is a
monosaccharide that is frequently detected as part of LPS.
The O-antigen and its biosynthesis requires four genes—rfbABCD. In general,
the genes involved in LPS biosynthesis have been reported to be upregulated during
early stages of colonization (Shidore et al. 2012; Camilios-Neto et al. 2014). The
mutation of one of the genes (in the mutation of either rfbB or rfbC) related to
rhamnose biosynthesis resulted in a 100-fold lower level of attachment to the root
surface and a lower endophytic colonization of maize (Z. mays) by H. seropedicae
SmR1 (Balsanelli et al. 2010) (Table 20.2).
The membrane protein in bacteria is also critical for the successful plant and
endophyte interactions. Of these, the muropeptide permease is necessary for peptidoglycan recycle of bacterial cell wall (Pinski et al. 2019). The sensitivity to SDS
and alterations in the LPS biosynthesis increased when the gene of this permease in
402
S.-C. Chun