Carbon dioxide fixation in the dark by photosynthetic bacteria in sulfide‐rich stratified lakes with oxic‐anoxic interfaces

Abstract

Carbon fixation was analyzed in a series of stratified lakes with oxygen-sulfide interfaces following 14 Cbicarbonate incorporation into oxygenic phototrophic, anoxygenic phototrophic (photosynthetic sulfur bacteria; PSB), and chemolithoautotrophic guilds (dark fixation processes), respectively. One of the lakes (Lake Cisó , Banyoles) was studied in more detail using microautoradiography of 14 C-labeled cells and microscopic observations during day and night. Dark carbon fixation was high for many of the depths sampled in all the lakes studied and there was a correspondence between carbon (C) fixation in the dark and abundance of photosynthetic purple sulfur bacteria (PSB). After in-situ dark incubations, microautoradiographies revealed labeled cells actively incorporating inorganic carbon belonging to both unidentified rod bacteria but also to PSB (Amoebobacter sp. and Thiocystis sp.). The concentration of labeled rod bacteria was very similar in light and dark incubations, as well as in day and night samplings, and had a tendency to increase in the anoxic dark hipolimnion. Surprisingly, PSB consistently incorporated inorganic carbon in dark incubations at high rates during the day but much less at night. This suggests that photosynthetic organisms are capable of substantial dark C fixation after being subjected to light, and that ''light dependent'' dark carbon-fixation activity is an issue that has to be carefully addressed in future experiments.

Vertical distribution of planktonic autotrophic thiobacilli and dark CO2 fixation rates in lakes with oxygen–sulfide interfaces

“…) and epilimnia (1.0 ± 2.1 µg C l -1 h -1 ) (n = 34, set of data available in Table 1 in Casamayor et al 2008). A lack of correspondence between the abundance of MPN thiobacilli and dark carbon fixation rates for the whole data set was observed (p = 0.060).…”

“…The lower water masses are rich in dissolved sulfate and carbonates brought by subsurface groundwater discharge. Here the deepest basin was sampled (Lake Grande de Estanya, SW position) with a thermocline located between 12 and 14 m. Only a few microbiological studies from this lake have been published (Ferrera et al 2004 and references therein, Casamayor et al 2008, Martínez-Alonso et al 2008, reporting blooms of the purple sulfur bacteria (PSB) Chromatium okenii and Thiocystis minor at the light-sulfide interface.…”

Metatranscriptomic Analyses of Plankton Communities Inhabiting Surface and Subpycnocline Waters of the Chesapeake Bay during Oxic-Anoxic-Oxic Transitions

“…The succession of bacterial taxonomic compositions and their metabolic activities along oxic-anoxic gradients have been investigated in sediments and water columns of permanently stratified ecosystems such as the Black Sea (23), Cariaco Basin (24), and the Arabian Sea (25). These investigations have detected novel pathways of autotrophy (e.g., anammox) (26), enhanced bacterial abundance and production at oxic/anoxic interfaces (27,28), and shifts in the composition of communities between oxic and anoxic waters (3). Oceanic environments with permanently stratified waters with oxygen-minimum zones (OMZs), such as in the East Tropical South Pacific, play a crucial role in global biogeochemical cycling, removing N from pelagic waters through denitrification and anammox to N 2 O and N 2 and enhancing S 2Ϫ concentrations through SO 4 2Ϫ reduction (29).…”

Epsilonproteobacteria Represent the Major Portion of Chemoautotrophic Bacteria in Sulfidic Waters of Pelagic Redoxclines of the Baltic and Black Seas

“…Extensive pelagic redoxclines are reported for the Black Sea (18,34,36), the Cariaco Basin (40,42), the Framvaren Fjord (27), the Mariager Fjord (45), the Baltic Sea (19), and freshwater lakes (6,9,14) and are often characterized by high dark CO 2 fixation rates. Characteristically, the peak of dark CO 2 fixation within the water column is often located below the chemocline, which we define as the shallowest appearance of sulfide (13).…”