dc.description.abstract | This work wants to investigate the role that microorganisms have in the
alteration and precipitation of minerals, in particular Ca-carbonates, on natural and
artefact rocks of archaeological interest in shallow marine environments. This finds
numerous applications in the recognizing of the abiotic vs. biotic nature of neoformed
minerals, such as in the reconstruction of depositional palaeoenvironment, in
astrobiology and in medicine. In addition, nanostructured microbially induced
minerals have several technical application varying from bioconservation,
bioremediation, biogrouting to biomedic. Furthermore, the knowledge of such complex interaction between bacterial
communities and hard substrates is essential for the preservation and the valorization
in situ of underwater cultural heritage, which represents a particularly important
element in the history of peoples. For this purpose, several key-samples of natural and artifact rocks, have been
collected in Santa Maria di Ricadi bay and in the archaeological submerged park of
Monasterace, respectively sited on the Tyrrhenian and Ionian coast of Southern
Calabria.
Optical and scanning electron microscopy (SEM) have been used for micro- and
nano-scale investigation of the role of microorganisms in the precipitation and
alteration of minerals. Observations showed that biofilms are characterized by: (1)
Skeletal elements, such as red algae, bryozoan, polychaete, bivalves and diatoms; (2)
bacteria such as cocci, bacilli, spirochaete, filamentous bacteria, often associated with
organic matter remains which result sometimes mineralized; (3) Neo-formed Cacarbonate
and pyrite minerals; (4) bioerosion elements, such as grooves and
boreholes Neo-formed Ca-carbonate minerals occur in Monasterace biofilms as sheet
deposits, triads or dumbbell- to spherical-shaped crystals; whereas in Santa Maria di
Ricadi as aphanitic and peloidal deposits. All these deposits result made up by an
assemblage of nanospheres, varying in diameter from 50 to 200 nm, tightly clotted
together. The co-existence of degraded EPS and bacteria, strictly associated with Cacarbonate
nanospheres, implies that the organic matter and the microbial metabolism
played a fundamental role in the precipitation of these minerals.
Moreover, in Monasterace biofilms, framboidal pyrite occur both in rock fracture
up to 2 mm below rock surface and within cavities of encrusting red algae. The
presence of framboidal pyrite and dumbbell- to spherical- shaped crystals imply they
formed in anoxic environment by sulphate reducers bacteria.
As regards bioerosion products, these results formed by epilithic, endolithic and
euendolithic organisms. In particular, in Ca-carbonate deposits forming part of Santa
Maria di Ricadi rock samples, an intricate net of grooves is produced by
cyanobacterium M. testarum.
All these elements suggest that biofilms are complex systems formed by
different biotic processes occurred both in oxic and anoxic conditions. Epilithic and
endolithic microorganisms resulted capable to modify chemical and physical microconditions
leading to the precipitation and alteration of diverse rocky materials, in
particular Calcium carbonate, in shallow marine environments. | en_US |