Biology Reference
In-Depth Information
We have further visualized for the irst time stress responses of
A.
oxydans
bacteria in response to the exposure to the toxic environment. Thus,
as illustrated in
Fig. 4.13c
,
the formation of a supramolecular crystalline
hexagonal structure on the surface of
bacteria exposed to 35-50
ppm Cr(VI) was observed. Since similar crystalline layers are not seen on
control samples (data are not shown here), this structure appears to be stress
induced in response to Cr(VI) exposure. At higher Cr(VI) concentrations, we
have observed the formation of microbial extracellular polymers, which are
seen in
Fig. 4.13d
,
to cover a small microbial colony.
Our AFM observations of the appearance of stress-induced layers on
the surfaces of
A. oxydans
bacteria exposed to Cr(VI) are consistent with
biochemical studies of stress responses of
A. oxydans
A. oxydans
bacteria. Thus, it was
reported that
grown with chromate concentrations above 40
mg/L signiicantly increased the production of a cell wall protein that had
an apparent molecular mass of 60 kDa.
59
Presumably, this protein could form
a highly organized particulate layer on the surface of
A. oxydans
bacteria
exposed to Cr(VI). The hexagonal stress-induced structure
(
Fig. 4.13c
)
is
formed by a protein with the size of ~10-11 nm. High-resolution images
(
Fig. 4.13c
, insert) reveal that these particles are oligomers, composed of
monomers with a size of ~5 nm. Assuming the globular shape of the protein,
this size corresponds well to the molecular mass of ~60 KDa.
It was suggested that reduction of Cr(VI) proceed on the cell wall.
60
This 60 kDa protein could be potentially involved in the reduction of Cr(VI).
We are currently developing procedures for
A. oxydans
high-resolution AFM
characterization of the surface architecture and structural dynamics of
metal-resistant bacteria in response to changes in the environment and
various chemical stimuli. It is expected that these experiments will improve
the fundamental understanding of bioremediation mechanisms.
The present technological and scientiic challenges are to elucidate the
relationships between the stress-induced organization and function of protein
and polymer complexes at bacterial cell wall surfaces, to understand how
these complexes respond to environmental changes and chemical stimulants
and to predict how they guide the formation of biogenic metal phases on the
cell surface.
The results presented here demonstrate that
in vitro
AFM is a powerful
tool for revealing the structural dynamics and architectural topography of
the microbial and cellular systems. AFM allows new approaches to high-
resolution real-time dynamic studies of single microbial cells under native
conditions. Environmental parameters (e.g. temperature, chemistry or gas
phase) can be easily changed during the course of AFM experiments, allowing
in vitro
Search WWH ::
Custom Search