Early-Branching Cyanobacteria Grow Faster and Upregulate Superoxide Dismutase Activity Under a Simulated Early Earth Anoxic Atmosphere.

The evolution of oxygenic photosynthesis during the Archean (4-2.5 Ga) required the presence of complementary reducing pathways to maintain the cellular redox balance. While the timing of the evolution of superoxide dismutases (SODs), enzymes that convert superoxide to hydrogen peroxide and O, within bacteria and archaea is not resolved, the first SODs appearing in cyanobacteria contained copper and zinc in the reaction center (CuZnSOD).

Exploring the influence of atmospheric CO and O levels on the utility of nitrogen isotopes as proxy for biological N fixation.

Biological N fixation (BNF) is traced to the Archean. The nitrogen isotopic fractionation composition (δN) of sedimentary rocks is commonly used to reconstruct the presence of ancient diazotrophic ecosystems. While δN has been validated mostly using organisms grown under present-day conditions; it has not under the pre-Cambrian conditions, when atmospheric O was lower and CO was higher.

The response of the marine nitrogen cycle to ocean acidification.

Ocean acidification (OA), arising from the influx of anthropogenically generated carbon, poses a massive threat to the ocean ecosystems. Our knowledge of the effects of elevated anthropogenic CO in marine waters and its effect on the performance of single species, trophic interactions, and ecosystems is increasing rapidly. However, our understanding of the biogeochemical cycling of nutrients such as nitrogen is less advanced and lacks a comprehensive overview of how these processes may change under OA.

Measuring bacterial activity and community composition at high hydrostatic pressure using a novel experimental approach: a pilot study.

In this pilot study, we describe a high-pressure incubation system allowing multiple subsampling of a pressurized culture without decompression. The system was tested using one piezophilic (Photobacterium profundum), one piezotolerant (Colwellia maris) bacterial strain and a decompressed sample from the Mediterranean deep sea (3044 m) determining bacterial community composition, protein production (BPP) and cell multiplication rates (BCM) up to 27 MPa. The results showed elevation of BPP at high pressure was by a factor of 1.

Climate change and regulation of hepatotoxin production in Cyanobacteria.

Harmful, bloom-forming cyanobacteria (CyanoHABs) are occurring with increasing regularity in freshwater and marine ecosystems. The most commonly occurring cyanobacterial toxins are the hepatotoxic microcystin and nodularin. These cyclic hepta- and pentapeptides are synthesised nonribosomally by the gene products of the toxin gene clusters mcy and nda, respectively.

Impact of diazotrophy on N stable isotope signatures of nitrate and particulate organic nitrogen: case studies in the north-eastern tropical Atlantic Ocean.

During two independent cruises in the north-eastern tropical Atlantic Ocean, we applied two different approaches to investigate the impact of diazotrophy on nitrogen stable isotope signatures in nitrate and particulate organic nitrogen (PON) of the food-web constituents. The first approach, used during the Poseidon cruise 348 in the Mauritanian upwelling, investigated the long-term influence of diazotrophy on the natural abundance of δ(15)N-NO(-)(3) and PON. The second approach, adopted during the Cape Verde field cruise, applied stable isotope tracer addition experiments.

ALGAE AS COMPETITORS FOR GLUCOSE WITH HETEROTROPHIC BACTERIA(1).

Dissolved organic carbon (DOC) constitutes the bulk of organic carbon in aquatic environments. The importance of DOC utilization by mixotrophic algae is unclear since heterotrophic bacteria are regarded as more efficient users. We tested the hypothesis that algae decrease the DOC concentration in the light to lower levels than in darkness resulting in competitive exclusion of heterotrophic bacteria according to the mechanistic competition theory.

Polymerized coumaric acid as a model substrate for terrestrial-derived dissolved organic carbon utilized by aquatic microorganisms.

It is now widely accepted that many surface waters receive more terrestrial carbon than assumed in the past, and that aquatic food webs are largely based on the supply of external dissolved organic carbon. However, very little information is available on how efficiently external carbon is utilized by microorganisms and transported to consumers of higher trophic levels. To address this issue, we prepared and tested polymers of 14C-p-coumaric acid (PCA) as a model substrate for terrestrial organic carbon.