PROKARYOTIC DISTRIBUTION ALONG A PH GRADIENT AT SHALLOW HYDROTHERMAL VENT OF VULCANO ISLAND (ITALY)

Shallow hydrothermal systems evoke primordial conditions
and represent models to investigate the effects of the
ocean acidification and warming on coastal environments.
Surface sediment samples were collected along a pH gradient,
at increasing distance from the acidic primary vent (PV).
Prokaryotic community abundance and diversity were examined
by 16S rRNA Fluorescence in situ Hybridization and
PCR-Denaturing Gradient Gel Electrophoresis (DGGE),
respectively. Bacteria numerically dominated over Archaea
in all sites, however the archaeal contribution to the entire
prokaryotic community increased at PV, where the lowest
pH value was recorded. As emerged by DGGE pattern
analyses, bacterial and archaeal richness and diversity
(Shannon index) increased in the vicinity of PV, indicating
that venting conditions result in high diversity of prokaryotic
communities. Phylogenetic analyses revealed that
Epsilonproteobacteria (chemosynthetic producers) prevailed
at PV, whereas Cyanobacteria (photosynthetic producers)
and Bacteroidetes (heterotrophs able to degrade complex
biopolymers) dominated at increasing distance from PV,
according with the increasing of pH. All achaeal sequences
from DGGE bands were affiliated with uncultured members
of Euryarchaeota and Crenarchaeota. Differently from
Euryarchaeota, Crenarchaeota increased with the proximity
to the acidic vent, determining a marked shift in the
archaeal population composition. Our results revealed the
contrasting effects of venting on the benthic bacterial and
archaeal communities. The proximity to the principal vent,
with a concomitant pH decreasing, seems to provide trophic
and ecological interactions resulting in assemblages of different
phylogenetic and metabolic microorganisms.