High abundance and dark CO₂ fixation of chemolithoautotrophic prokaryotes in anoxic waters of the Baltic Sea

Abstract

We determined the abundance and distribution of chemolithoautotrophic prokaryotes in the redoxcline in two basins (Gotland Deep, Landsort Deep) of the central Baltic Sea by combining dark CO 2 fixation measurements with flow cytometric cell sorting. Maximum CO 2 fixation rates were recorded in sulfidic waters about 20 m below the chemocline. Flow cytometric analyses of deoxyribonucleic acid (DNA)-stained bacterioplankton revealed the existence of at least five different prokaryotic clusters in water samples collected below the chemocline. Dark CO 2 fixation in these clusters was determined by flow cytometric sorting after anoxic incubations with NaH 14 CO 3 tracer. Two clusters, representing about 30% of total prokaryotes, were responsible for 65% to 100% of the total dark fixation. Calculated cell-specific CO 2 fixation rates in the two basins ranged from 3.5 to 24.7 fg C cell 21 d 21 and suggested that these clusters are dominated by chemolithoautotrophic prokaryotes. Mean cell-specific fixation rates reached more than 10 fg C cell 21 d 21 in most cases, indicating relatively high growth rates (doubling times 1-2 d) of chemolithoautotrophic prokaryotes. Our results provide the first evidence of such high cellspecific CO 2 uptake and abundance of chemolithoautotrophic prokaryotes in a pelagic marine environment. However, the identity of the organisms as well as the mechanisms fueling CO 2 dark fixation in the anoxic zone remain unknown.

Morphological and molecular approaches reveal highly stratified protist communities along Baltic Sea pelagic redox gradients

“…During our observation period at Gotland Deep in 2007, 2008 and Landsort Deep in 2008, we found a characteristic water column stratification for the central Baltic Sea (Jost et al 2008, as exemplified for the Gotland Deep in 2007 in Fig. 1.…”

“…In contrast to numerous detailed studies on the prokaryotic assemblages (e.g. Labrenz et al 2007, Jost et al 2008, Grote et al 2012, protist related studies of Baltic Sea redoxclines are limited to a few microscopy-based approaches (Setälä 1991, Detmer et al 1993) and one single 18S rRNA-based diversity study, covering 2 water depths of the Gotland Deep ). Two recent studies, which also provide data for different protist functional groups, focused on the role of protist grazing and viral lysis as prokaryotic mortality factors in the redox gradient (Anderson et al , 2013.…”

Energy Transfer Through Food Webs at Hydrothermal Vents: Linking the Lithosphere to the Biosphere

“…Later, stable isotopes showed that heterotrophic fauna generally do not consume these visually dominant foundation species (Fisher et al, 1994), which can comprise more than 90% of the community biomass (Govenar et al, 2005). Instead, the majority of vent-endemic fauna appear to feed on free-living microbes Breea Govenar (bgovenar@ric.edu (Menge and Sutherland, 1987 (Taylor et al, 2001), the Black Sea (Yilmaz et al, 2006), and the Baltic Sea (Jost et al, 2008). Active areas of research at hydrothermal vents are focused on the phylogenetic and physiological diversity of chemoautotrophic bacteria and archaea (e.g., Takai et al, 2006), the relative importance of different carbonfixation pathways in primary production (e.g., Hugler and Sievert, 2011), and the variation in diets among consumers.…”

A Bioreactor Approach to Investigate the Linkage between Methane Oxidation and Nitrate/Nitrite Reduction in the Pelagic Oxic-Anoxic Transition Zone of the Central Baltic Sea

“…The number of bacterial cells in the enrichment culture was quantified using flow cytometry (FACS Calibur flow cytometer, Becton and Dickinson) as described by Jost et al (2008). Briefly, duplicate samples of 1 ml were taken weekly from the enrichment culture under stirred conditions and preserved with 100 µl paraformaldehyde.…”