| Congresso Brasileiro de Microbiologia 2023 | Resumo: 529-1 | ||||
Resumo:The Twilight Zone is found between 200 m and 1000 m in the water column and
holds the highest species richness in the pelagic environment. Its upper section
is the lower boundary of the euphotic zone, where it interfaces with the
gradients of the epipelagic zone but receives insufficient light for
photosynthesis. Conversely, its lower section lacks adequate irradiation even for predator visibility, thereby impacting the activity of macro and microorganisms. Both the heterogeneity of this zone and the diverse metabolism of microorganisms inhabiting it play significant roles in biogeochemical cycles and
organic matter flow, which are crucial processes for maintaining life in the
ocean. Located in the Southeast region of Brazil, the Santos Basin (SB) is the
country's largest offshore sedimentary basin and has significant participation in
oil and natural gas production. As part of the cooperative project between
IO-USP and PETROBRAS/CENPES "Santos Basin Environmental
Characterization", we conducted a study to compare the diversity and
distribution of prokaryotes inhabiting two different depths in the SB Twilight
Zone. We collected water samples from 29 oceanographic stations across the
SB, at depths of 250 m, which is under the influence of the South Atlantic
Central Water, and 900 m, which is under the influence of the Atlantic
Intermediate Water. We examined planktonic microbial communities using flow
cytometry and high-throughput sequencing of the 16S rRNA gene (regions V4
and V5). The results were then processed using the Phyloseq R package. A
total of 3x106 non-photosynthetic prokaryotic cells were detected in the SB, of
which 2x106 were reported at 250 m, against 6x105 reported at 900 m,
representing 80,4% and 19,6% of carbon biomass, respectively. Microbial
community beta-diversity was primarily clustered according to depth, and
Shannon diversity was higher at 250 m. A total of 7.464 prokaryotic amplicon
sequence variants (ASVs) were retrieved from all samples, of which 1019 were
present in both depths, 3261 were exclusively found at 250 m, and 3184 at 900
m. Also, approximately 70% of families found at both depths had distinct
members corresponding to each depth. The domain Bacteria showed higher
abundance (59%) over Archaea (41%), even with chemosynthetic
Nitrosopumilales (41%, Nitrososphaera), dominating all samples. Next,
heterotrophic Pelagibacterales (Alphaproteobacteria) comprised 20% of the
total, and Alteromonadales (Gammaproteobacteria) 7%. In contrast, the relative abundance of the subsequent groups differed between the depths:
Flavobacteriales (3%, Flavobacteriia) and Planctomycetales (2%,
Planctomycetia) at 250 m; Pirellulales (4%, Plantomycetia) and
Thiomicrospirales ( 1%, Gammaproteobacteria) at 900 m. Our results indicate a
vertical stratification of microbial communities, with higher carbon biomass and
diversity at 250 m in the BS. This adaptation of groups is in accordance with
previous studies that show the same pattern of stratification by water masses
for microbial communities and reinforces the vertical heterogeneity of the
Twilight Zone. In addition, prevalent orders identified in this study align with
groups found in the North Atlantic Ocean and significantly contribute to nitrogen
and carbon cycles, particularly through N2 and CO2 fixation. These findings
provide valuable insights into the complex dynamics of the twilight zone and its
significance for maintaining life in the South Atlantic Ocean Palavras-chave: bacterioplankton, nutrient cycling, south atlantic ocean, twilight zone Agência de fomento:Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) | |||||