Oxygen contents, sulfate concentrations, and changes of IPLs under different storage conditions of samples from ODP Leg 204 and IODP Expedition 311

We have studied the effects of slow infiltration of oxygen on microbial communities in refrigerated legacy samples from ocean drilling expeditions. Storage was in heat-sealed, laminated foil bags with a N2 headspace for geomicrobiological studies. Analysis of microbial lipids suggests that Bacteria were barely detectable in situ but increased remarkably during storage. Detailed molecular examination of a methane-rich sediment horizon showed that refrigeration triggered selective growth of ANME-2 archaea and a drastic change in the bacterial community. Subsequent enrichment targeting methanogens yielded exclusively methylotrophs, which were probably selected for by high sulfate levels caused by oxidation of reduced sulfur species. We provide recommendations for sample storage in future ocean drilling expeditions.

Stareso MedSeA mesocosm experiment: field and perturbation studies 2012

A joint mesocosm experiment took place in June/July 2012 in Corsica (bay of Calvi, Stareso station;http://www.stareso.com/) as part of the european MedSeA project. Nine mesocosms (52 m**3) were deployed over a 20 days period and 6 different levels of pCO2 and 3 control mesocosms (about 450 µatm), were used, in order to cover the range of pCO2 anticipated for the end of the present century. During this experiment, the potential effects of these perturbations on chemistry, planktonic community composition and dynamics including: eucaryotic and prokaryotic species composition, primary production, nutrient and carbon utilization, calcification, diazotrophic nitrogen fixation, organic matter exudation and composition, micro-layer composition and biogas production were studied by a group of about 25 scientists from 8 institutes and 6 countries. This is one of the first mesocosm experiments conducted in oligotrophic waters. A blog dedicated to this experiment can be viewed at: http://medseastareso2012.wordpress.com/.

Tab. 1: Summary of available data about antifreeze peptides of polar fish

In the blood of Antarctic notothenioid and Arctic gadiform fishes, freezing is inhibited by antifreeze glycopeptide macromolecules (AFGP). These antifreeze molecules are built up of repeating tripeptide units (Ala-Ala-Thr)n, to which the disaccharide fl-D-galactosyl-(1->3)a-N-acetyl-D-galactosamine is linked through the hydroxyl oxygen of the threonyl residue. Species of Liparididae, Zoarcidae, Cottidae and Pleuronectidae synthezise only unglycosylated antifreeze peptides (AFP). It could be demonstrated for the Antarctic silverfish Pleuragramma antarcticum that the synthesis of AFGP is not constitutive but rather regulated by water temperature. Moreover a novel glycopeptid was isolated and characterised from P. antarcticum, the Pleuragramma-antifreeze glycopeptid (PAGP). The level of antifreeze concentration was dependent on the ambient water temperature, the depth of distribution, the life cycle and the evolution of the species. Surprisingly, detectable AFGPs in perciform fish of the Antarctic and gadiform fish of the Arctic and Antarctic could illustrate, that before the continental drift occurred a precursor glycopeptid existed, and that the existence of freezing resistance in some species reflects the past glaciation. The wide distribution and high heterogeneity of AFPs point to the assumption that these peptides are results of cold shock stress responses.

Seawater carbonate chemistry and processes during experiments with cyanobacterium Trichodesmium (IMS101), 2009

We investigated carbon acquisition by the N2-fixing cyanobacterium Trichodesmium IMS101 in response to CO2 levels of 15.1, 37.5, and 101.3 Pa (equivalent to 150, 370, and 1000 ppm). In these acclimations, growth rates as well as cellular C and N contents were measured. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, and CO2 and HCO3- fluxes were measured using membrane inlet mass spectrometry and the 14C disequilibrium technique. While no differences in growth rates were observed, elevated CO2 levels caused higher C and N quotas and stimulated photosynthesis and N2 fixation. Minimal extracellular CA (eCA) activity was observed, indicating a minor role in carbon acquisition. Rates of CO2 uptake were small relative to total inorganic carbon (Ci) fixation, whereas HCO{3 contributed more than 90% and varied only slightly over the light period and between CO2 treatments. The low eCA activity and preference for HCO3- were verified by the 14C disequilibrium technique. Regarding apparent affinities, half-saturation concentrations (K1/2) for photosynthetic O2 evolution and HCO3- uptake changed markedly over the day and with CO2 concentration. Leakage (CO2 efflux : Ci uptake) showed pronounced diurnal changes. Our findings do not support a direct CO2 effect on the carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) but point to a shift in resource allocation among photosynthesis, carbon acquisition, and N2 fixation under elevated CO2 levels. The observed increase in photosynthesis and N2fixation could have potential biogeochemical implications, as it may stimulate productivity in N-limited oligotrophic regions and thus provide a negative feedback in rising atmospheric CO2 levels.

Biogeochemical processes in anoxic sediment from Lake Plußsee, Germany

In anoxic environments, volatile methylated sulfides like methanethiol (MT) and dimethyl sulfide (DMS) link the pools of inorganic and organic carbon with the sulfur cycle. However, direct formation of methylated sulfides from reduction of dissolved inorganic carbon has previously not been demonstrated. When studying the effect of temperature on hydrogenotrophic microbial activity, we observed formation of DMS in anoxic sediment of Lake Plußsee at 55 °C. Subsequent experiments strongly suggested that the formation of DMS involves fixation of bicarbonate via a reductive pathway in analogy to methanogenesis and engages methylation of MT. DMS formation was enhanced by addition of bicarbonate and further increased when both bicarbonate and H2 were supplemented. Inhibition of DMS formation by 2-bromoethanesulfonate points to the involvement of methanogens. Compared to the accumulation of DMS, MT showed the opposite trend but there was no apparent 1:1 stoichiometric ratio between both compounds. Both DMS and MT had negative d13C values of -62 per mil and -55 per mil, respectively. Labeling with NaH**13CO3 showed more rapid incorporation of bicarbonate into DMS than into MT. The stable carbon isotopic evidence implies that bicarbonate was fixed via a reductive pathway of methanogenesis, and the generated methyl coenzyme M became the methyl donor for MT methylation. Neither DMS nor MT accumulation were stimulated by addition of the methyl-group donors methanol and syringic acid or by the methyl-group acceptor hydrogen sulphide. The source of MT was further investigated in a H2**35S labeling experiment, which demonstrated a microbially-mediated process of hydrogen sulfide methylation to MT that accounted for only <10% of the accumulation rates of DMS. Therefore, the major source of the 13C-depleted MT was neither bicarbonate nor methoxylated aromatic compounds. Other possibilities for isotopically depleted MT, such as other organic precursors like methionine, are discussed. This DMS-forming pathway may be relevant for anoxic environments such as hydrothermally influenced sediments and fluids and sulfate-methane transition zones in marine sediments.

Oligotrophic bacteria from the Antarctic Ocean

From enrichment cultures in dialysis chambers held in natural seawater tanks, 104 strains were isolated and kept in culture. All strains proved to be Gram-negative and psychrotrophic, having optimum growth temperatures of between 20 and 24 °C. Maximal growth temperatures were 30 to 37 °C, or even higher. With 55 isolates, substrate utilizations in Biolog MicroPlates were determined, and the obtained metabolic fingerprints used for clustering. Five groups could be distinguished at the 80% similarity level. Fifteen strains belonged to cluster 1, seven strains to cluster 2, and each of the clusters 3 and 4 contained nine strains. Cluster 5 can be divided into subcluster 5a and 5b, with 6 strains showing a few substrates metabolized, and 9 strains without any reactions, or weak reactions for one or two substrates, respectively. Each cluster could be characterized by specific metabolic fingerprints. Strains from cluster 1 metabolized N-acetyl-D-glucosamine, alpha-hydroxybutyric acid and gamma-hydroxybutyric acid, strains from cluster 2 citric acid, formic acid, thymidine and putrescine, strains from cluster 3 glycyl-L-aspartic acid, glycyl-L-glutamic acid, L-threonine and inosine, whereas strains from cluster 4 metabolized alpha-cyclodextrin and N-acetyl-D-galactosamine, typically. Methylamine was not utilized by the isolates, but strains from cluster 1, 2 and 3 could grow on basal seawater agar. Morphological characteristics and photomicrographs of the oligotrophic strains are presented. Due to their typical morphologies and ampicillin resistence, the nine strains from cluster 3 can be regarded as new species of the genus Planctomyces. These bacteria have not been cultivated before.