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

28j 2 Physicochemical Approaches to Studying Plant Growth Promoting Rhizobacteria
Figure 2.4 Typical emission Mössbauer
spectra of (a) aqueous suspension of live cells
of A. brasilense Sp245 in the culture medium
(frozen 2 min after contact with 57 Co II traces)
and (b) the cell-free supernatant liquid rapidly
frozen in liquid nitrogen (spectra collected
at T = 80 K; velocity scale calibrated relative
to a-Fe; intensities converted to the
absorption convention) [37].
For each spectrum, the relevant subspectra
(quadrupole doublets) are shown which
contributed to the resulting spectrum
(solid-line envelope) obtained by computer
fitting to the experimental data (points with
vertical error bars). The positions of the
spectral components (quadrupole
doublets) are indicated by horizontal square
brackets above the zero lines.
It should be mentioned that primary binding of heavy metals by the cell surface in
Gram-negative bacteria is mediated by capsular polysaccharide (PS, particularly
carboxylated acidic PS), lipopolysaccharide (LPS, including phosphate LPS moieties),
and proteinaceous materials [8,10,37]. In A. brasilense, these biopolymers and
their covalently bound complexes characteristic of the cell surface [2] are believed to
be involved in contact interactions with plant roots and in bacterial cell aggregation
[2,25]. Thus, their interactions with metal ions in metal-contaminated soil can
interfere with the processes of molecular plant–bacterial interactions, which must
be investigated in detail. It has to be noted also that the above-described microbiological
EMS studies can be applied for revealing possible biotransformations of
environmentally significant 60 Co radionuclide traces that can result in its microbially
mediated migration in soils and aquifers [10,12,38].