『Abstract
Understanding the effects of microbiota on mineral alteration
requires the ability to recognize evidence of bacteria-promoted
dissolution on mineral surfaces. Although siderophores are known
to promote mineral dissolution, their effects on mineral surfaces
are not well known. We have utilized atomic force microscopy (AFM),
X-ray photoelectron spectroscopy (XPS), and Mirau vertical scanning
interferometry (VSI) to investigate surfaces after incubation
with the siderophore desferrioxamine-B mesylate (DFAM) and under
colonies of bacteria. Iron-silicate glass planchets chemically
similar to hornblende were incubated in buffered growth medium
with siderophore-producing bacteria (Bacillus sp.) for
346 days with parallel abiotic experiments conducted with and
without 240 μM DFAM, with and without 0.01 g l-1 of
microbially produced extracellular polysaccharides (EPS, alginate
or xanthan gum). Some glass planchets were protected by dialysis
tubing from direct contact with the EPS. Weekly sampling and analysis
of all filtered sample solutions showed negligible Fe and Al release
in the control experiments and significant release of Fe and Al
in the presence of DFAM, with negligible changes in pH. Concentration
of Fe in the filtered solutions after incubation with bacteria
was below detection, consistent with uptake of Fe by cells. Release
of Fe, Al, and Si in control, xanthan-only, and alginate-only
experiments was negligible. Release of these elements was enhanced
in all experiments containing DFAM, and greatest in alginate+DFAM
experiments.
AFM and VSI analyses reveal widespread, small etch pits and greater
root mean squared roughness on siderophore-exposed surfaces and
fewer, localized, larger etch pits on bacteria-exposed surfaces.
This is the first documented case of etch pit development during
siderophore-promoted dissolution. Roughness was not affected by
the growth medium, alginate, or xanthan gum alone. The roughness
trends among samples correlate with trends in Fe depletion documented
by XPS. Enhanced dissolution and roughness cannot be attributed
to direct contact with EPS because no significant chemical or
physical differences were observed between surfaces directly exposed
to EPS and those protected by dialysis tubing. Acetate released
from the EPS may have enhanced the siderophore-promoted dissolution.
Siderophores produced by Bacillus sp. may be responsible
for some of the ‘biopits.’ The difference in size and distribution
of the biopits may be related to colonization.
Keywords: Siderophores; Etch pits; Hornblende; Desferrioxamine;
Biofilms 』
1. Introduction
1.1. Surface colonization
1.2. Siderophores
2. Materials and methods
2.1. Experimental setup
2.2. XPS
2.3. AFM
2.4. VSI
3. Results
3.1. Solution chemistry
3.2. Surface chemistry
3.3. Etch pits
3.4. RMS roughness
4. Dissolution
4.1. Surface effects of siderophores
4.2. Surface effects of EPS
4.3. Surface effects of Bacillus sp.
5. Conclusions
Acknowledgements
References