Rhizobia-diatom symbiosis fixes missing nitrogen in the ocean.

Nitrogen (N) fixation in oligotrophic surface waters is the main source of new nitrogen to the ocean and has a key role in fuelling the biological carbon pump. Oceanic N fixation has been attributed almost exclusively to cyanobacteria, even though genes encoding nitrogenase, the enzyme that fixes N into ammonia, are widespread among marine bacteria and archaea. Little is known about these non-cyanobacterial N fixers, and direct proof that they can fix nitrogen in the ocean has so far been lacking.

Temperature variability interacts with mean temperature to influence the predictability of microbial phenotypes.

Despite their relatively high thermal optima (T ), tropical taxa may be particularly vulnerable to a rising baseline and increased temperature variation because they live in relatively stable temperatures closer to their T . We examined how microbial eukaryotes with differing thermal histories responded to temperature fluctuations of different amplitudes (0 control, ±2, ±4°C) around mean temperatures below or above their T . Cosmopolitan dinoflagellates were selected based on their distinct thermal traits and included two species of the same genus (tropical and temperate Coolia spp.

Terrestrial-type nitrogen-fixing symbiosis between seagrass and a marine bacterium.

Symbiotic N-fixing microorganisms have a crucial role in the assimilation of nitrogen by eukaryotes in nitrogen-limited environments. Particularly among land plants, N-fixing symbionts occur in a variety of distantly related plant lineages and often involve an intimate association between host and symbiont. Descriptions of such intimate symbioses are lacking for seagrasses, which evolved around 100 million years ago from terrestrial flowering plants that migrated back to the sea.

Niche partitioning by photosynthetic plankton as a driver of CO-fixation across the oligotrophic South Pacific Subtropical Ocean.

Oligotrophic ocean gyre ecosystems may be expanding due to rising global temperatures [1-5]. Models predicting carbon flow through these changing ecosystems require accurate descriptions of phytoplankton communities and their metabolic activities [6]. We therefore measured distributions and activities of cyanobacteria and small photosynthetic eukaryotes throughout the euphotic zone on a zonal transect through the South Pacific Ocean, focusing on the ultraoligotrophic waters of the South Pacific Gyre (SPG).

Purple sulfur bacteria fix N via molybdenum-nitrogenase in a low molybdenum Proterozoic ocean analogue.

Biological N fixation was key to the expansion of life on early Earth. The N-fixing microorganisms and the nitrogenase type used in the Proterozoic are unknown, although it has been proposed that the canonical molybdenum-nitrogenase was not used due to low molybdenum availability. We investigate N fixation in Lake Cadagno, an analogue system to the sulfidic Proterozoic continental margins, using a combination of biogeochemical, molecular and single cell techniques.

Genomic variation and biogeography of Antarctic haloarchaea.

Background: The genomes of halophilic archaea (haloarchaea) often comprise multiple replicons. Genomic variation in haloarchaea has been linked to viral infection pressure and, in the case of Antarctic communities, can be caused by intergenera gene exchange. To expand understanding of genome variation and biogeography of Antarctic haloarchaea, here we assessed genomic variation between two strains of Halorubrum lacusprofundi that were isolated from Antarctic hypersaline lakes from different regions (Vestfold Hills and Rauer Islands).

A plasmid from an Antarctic haloarchaeon uses specialized membrane vesicles to disseminate and infect plasmid-free cells.

The major difference between viruses and plasmids is the mechanism of transferring their genomic information between host cells. Here, we describe the archaeal plasmid pR1SE from an Antarctic species of haloarchaea that transfers via a mechanism similar to a virus. pR1SE encodes proteins that are found in regularly shaped membrane vesicles, and the vesicles enclose the plasmid DNA.

Glycerol metabolism of haloarchaea.

Haloarchaea are heterotrophic members of the Archaea that thrive in hypersaline environments, often feeding off the glycerol that is produced as an osmolyte by eucaryotic Dunaliella during primary production. In this study we analyzed glycerol metabolism genes in closed genomes of haloarchaea and examined published data describing the growth properties of haloarchaea and experimental data for the enzymes involved. By integrating the genomic data with knowledge from the literature, we derived an understanding of the ecophysiology and evolutionary properties of glycerol catabolic pathways in haloarchaea.

Ecophysiological Distinctions of Haloarchaea from a Hypersaline Antarctic Lake as Determined by Metaproteomics.

Unlabelled: Deep Lake in the Vestfold Hills is hypersaline and the coldest system in Antarctica known to support microbial growth (temperatures as low as -20°C). It represents a strong experimental model because the lake supports a low-complexity community of haloarchaea, with the three most abundant species totaling ∼72%. Moreover, the dominant haloarchaea are cultivatable, and their genomes are sequenced.

Antarctic archaea-virus interactions: metaproteome-led analysis of invasion, evasion and adaptation.

Despite knowledge that viruses are abundant in natural ecosystems, there is limited understanding of which viruses infect which hosts, and how both hosts and viruses respond to those interactions-interactions that ultimately shape community structure and dynamics. In Deep Lake, Antarctica, intergenera gene exchange occurs rampantly within the low complexity, haloarchaea-dominated community, strongly balanced by distinctions in niche adaptation which maintain sympatric speciation. By performing metaproteomics for the first time on haloarchaea, genomic variation of S-layer, archaella and other cell surface proteins was linked to mechanisms of infection evasion.