In vitro measurements, predictions, and geochemical estimates of the balance between gross primary production (GPP) and community respiration (CR) in the open ocean do not agree. This has generated an active debate about the carbon balance in unproductive pelagic marine ecosystems. The analysis of generalized GPP:CR relationships that sustains this debate assumes a continuous trophic gradient or the simple partition of the World Ocean into productive and unproductive regimes. We measured euphotic zone GPP and CR along a latitudinal (40Њ N-30Њ S) transect across the Atlantic Ocean, which included two openocean oligotrophic provinces: the eastern area of the North Atlantic Subtropical Gyre (NAST-E) and the center of the South Atlantic Gyre (SATL). Net heterotrophy prevailed in the euphotic zone of the NAST-E, while the plankton community in the central SATL was net autotrophic. A review of published studies of net plankton metabolism in the open ocean substantiates this geographic pattern, suggesting the existence of different trophic dynamics in similarly unproductive planktonic communities that might be characterized by the relative importance of local vs. allochthonous sources of organic matter. No universal relationship appears to exist between the magnitude of photosynthesis of a pelagic ecosystem and its net metabolism. We tested the published GPP:CR relationships and found that each one was only able to correctly predict GPP:CR balances in either the heterotrophic NAST-E or the autotrophic SATL, thus confirming that the geographic pattern in net community metabolism is related to the functional diversity of unproductive oceanic ecosystems.

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A key step for nitrate assimilation in photosynthetic eukaryotes occurs within chloroplasts, where nitrite is reduced to ammonium, which is incorporated into carbon skeletons. The Nar1 gene from Chlamydomonas reinhardtii is clustered with five other genes for nitrate assimilation, all of them regulated by nitrate. Sequence analysis of genomic DNA and cDNA of Nar1 and comparative studies of strains having or lacking Nar1 have been performed. The deduced amino acid sequence indicates that Nar1 encodes a chloroplast membrane protein with substantial identity to putative formate and nitrite transporters in bacteria. Use of antibodies against NAR1 has corroborated its location in the plastidic membrane. Characterization of strains having or lacking this gene suggests that NAR1 is involved in nitrite transport in plastids, which is critical for cell survival under limiting nitrate conditions, and controls the amount of nitrate incorporated by the cells under limiting CO(2) conditions.

Abstract. The biological production of calcium carbonate (CaCO3), a process termed calcification, is a key term in the marine carbon cycle. A major planktonic group responsible for such pelagic CaCO3 production (CP) are the coccolithophores, single-celled haptophytes that inhabit the euphotic zone of the ocean. Satellite-based estimates of areal CP are limited to open-ocean waters, with current algorithms utilising the unique optical properties of the cosmopolitan bloom-forming species Emiliania huxleyi, whereas little understanding of the optical properties and environmental responses by species other than E. huxleyi are currently available to parameterise algorithms or models. To aid future areal estimations and validate future modelling efforts we have constructed a database of 2765 CP measurements, the majority of which were measured using 12 to 24 h incorporation of radioactive carbon (14C) into acid-labile inorganic carbon (CaCO3). We present data collated from over 30 studies covering the period from 1991 to 2015, sampling the Atlantic, Pacific, Indian, Arctic and Southern oceans. Globally, CP in surface waters (

A multispecies bacterial community including Microbacterium fakhimi sp. nov., Stenotrophomonas goyi sp. nov., and Bacillus cereus greatly promoted sustained hydrogen production by the microalga Chlamydomonas reinhardtii when cocultivated in mannitol- and yeast extract-containing medium (up to 313 mLxx L-1). Alga viability was also largely prolonged in the cocultures (>45 days) without any nutrient supplementation. Among the bacterial community, Microbacterium fakhimi sp. nov. was the main responsible for the hydrogen production improvement. Nonetheless, the use of the entire bacterial community allowed a better growth of the alga during hydrogen production. Chlamydomonas reinhardtii and Microbacterium fakhimi sp. nov. established a mutualistic association, based on the release of ammonium and acetic acid from the bacterium, while the alga provided sulfur-containing metabolites and complemented the bacterial auxotrophy for biotin and thiamine. This study uncovers the potential of the Chlamydomonas-bacteria consortia for durable and stable H2 production while allowing the simultaneous production of biomass.