Geology Reference
In-Depth Information
(%, w/v): 1% yeast extract; 0.5% proteose peptone;
0.1% glucose; and 3.5% NaCl. This medium was
supplied with calcium and magnesium acetate to
adjust the Mg/Ca molar ratio to 7.4. To obtain a
semi-solid medium, 20 g L
1
Bacto-Agar (Difco)
was added. After the pH was adjusted to 7.0 with
0.1 M KOH, the medium was sterilized at 121°C
for 20 minutes.
Microorganisms
The bacterial strains used for this study were
isolated from the uppermost part of the micro-
bial mat in Brejo do Espinho lagoon and are des-
ignated Strain BE1 and BE2. These strains are
heterotrophic, obligate aerobic bacteria. In order
to obtain pure cultures of these single strains,
dilution series from the isolated samples taken
from the microbial mat were inoculated onto Petri
dishes containing the culture medium described
above and incubated aerobically at 30°C. The
Petri dishes were examined periodically to deter-
mine if the colonies were able to induce mineral
precipitation.
The colonies forming a visible concentric
corona of carbonate minerals were isolated. These
pure strains were selected for phylogenetic 16S
ribosomal deoxyribonucleic acid (rDNA) ana-
lysis (Institut für medizinische ünd molekulare
Diagnostic AG, Zürich). The sequences obtained
(ranging from 794 to 802 base pairs) were com-
pared with the National Center for Biotechnology
Information (NCBI) database. The results from the
approximate phylogenetic affi liation revealed that
the closest relative of strain BE1 is
Virgibacillus
marismortui
(NCBI, accession number AJ009793)
with 99.8% homology, and strain BE2 has a
100% homology to
Marinobacter
sp. NT N31.
Strain BE1 and BE2 are hereafter designated as
V. marismortui
and
Marinobacter
sp., respectively.
V. marismortui
(Heyrman
et al
., 2003) was fi rst
isolated in 1999 from the Dead Sea (Arahal
et al
.,
1999), and was originally described as
Bacillus
marismortui
.
Marinobacter
sp. NT N31 was fi rst
isolated from deep-sea sediment below a micro-
bial mat in 3708 m water depth (Okamoto &
Naganuma, unpublished).
5mm
Fig. 2.
Brejo do Espinho microbial mat with character-
istic coloured layers. Green corresponds to cyanobacteria,
pink presumably to purple sulphur bacteria, dark brown
to zone of anaerobic metabolism and white to carbonate
biominerals.
The climatic conditions in this area are peculiar
due to the occurrence of an upwelling zone off-
shore that contributes to the semi-arid climate
characteristic for the region. These special condi-
tions lead to a strong interannual variability of the
regional climate, whereby evaporation exceeds
precipitation (Barbiére, 2002).
Brejo do Espinho lagoon water has a typical
seawater Mg/Ca molar ratio of ~ 5, indicating
a seawater origin modifi ed by evaporation and
dilution processes (van Lith
et al
., 2002; Moreira
et al
., 2004). Brejo do Espinho sediment contains
nearly stoichiometric dolomite, which appears to
precipitate predominantly in periods of the year
with the highest salinities (van Lith
et al
., 2002).
Thick, multicoloured microbial mats develop on
the surface of Brejo do Espinho during fl ooded
periods, which are controlled by two factors, sur-
face runoff during the wet season versus infl ux of
seawater through the dunes during the dry season.
The microbial mat exhibits a stratifi cation of mat-
forming microbial communities, which is visible
as different coloured layers (Fig. 2). For this study,
microorganisms were isolated from the uppermost
layers where oxygen tends to persist.
METHODS
Study of mineral formation
The ability of
V. marismortui
and
Marinobacter
sp. cells to induce carbonate precipitation was
tested using the prepared semi-solid medium
D-1 because bacterial carbonates are commonly
Culture medium
The culture medium (D-1) used in our laboratory
experiments has the following composition
