Genomic evidence for inter-class host transition between abundant streamlined heterotrophs by a novel and ubiquitous marine Methylophage

The methylotrophic OM43 clade are Gammaproteobacteria that comprise some of the smallest free-living cells known with highly streamlined genomes. OM43 represents an important microbial link between marine primary production and return of carbon back to the atmosphere. Bacteriophages shape microbial communities and are major drivers of mortality and global marine biogeochemistry. Recent cultivation efforts have brought the first viruses infecting members of the OM43 clade into culture. Here we characterize a novel myophage infecting OM43, called Melnitz. Melnitz was isolated independently on three separate occasions (with isolates sharing >99.95% average nucleotide identity) from water samples from a subtropical ocean gyre (Sargasso Sea) and temperate coastal (Western English Channel) systems. Metagenomic recruitment from global ocean viromes confirmed that Melnitz is globally ubiquitous, congruent with patterns of host abundance. Bacteria with streamlined genomes such as OM43 and the globally dominant SAR11 clade use riboswitches as an efficient method to regulate metabolism. Melnitz encodes a two-piece tmRNA (ssrA), controlled by a glutamine riboswitch, providing evidence that riboswitch use also occurs for regulation during phage infection of streamlined heterotrophs. Virally encoded tRNAs and ssrA found in Melnitz were phylogenetically more closely related to those found within the alphaproteobacterial SAR11 clade and their associated myophages than those within their gammaproteobacterial hosts. This suggests the possibility of an ancestral inter-class host transition event between SAR11 and OM43. Melnitz and a related myophage that infects SAR11 were unable to infect hosts of the SAR11 and OM43, respectively, suggesting host transition rather than a broadening of host range.

Decadal and Multidecadal Variability in ERSSTv5 Global SST During 1879-2018

Decadal and multi-decadal variability in the ERSSTv5 global SST dataset are studied in terms of implicit fast (noise) and slow (signal) processes that affect variability on decadal time scales. Using a new method that better estimates the fast, or noise, component of decadal variability, estimates of the modes of variability in the slow component are possible. The fast component of decadal variability has a leading fast mode, which explains 62% of the variance, and it is shown that this fast variability, or decadal climate noise, is well represented by any of the indices associated with intra-decadal or interannual variability in the tropical Pacific Ocean.Three slow modes are identified, representing 69% of the slow multi-decadal variance, after removing the radiative forcing trend. These modes are shown to be related to variability in the Atlantic Multi-decadal Oscillation (AMO), and SST multi-decadal variability in the Central Western Pacific and in the Indian Ocean gyre region, respectively. The first and third slow modes represent two phases of a propagating mode with a period of about 80 years. The second slow mode represents multi-decadal variability of the Western Pacific Warm Pool which is less robust than the other two and shown to be weakly related to the AMO with a lag of about 30 years; fast variability in this region is related to the leading fast mode. Three regions of significant slow variability are identified south of Australia, south of Africa and near the Drake Passage in association with the Antarctic Circumpolar Current.

Bio-GO-SHIP: Shifts in bacterial communities reveal subtle biogeochemical regimes across the Indian Ocean

<p>Historically, our understanding of ecological responses to biogeochemical gradients and physical dynamics in the Indian Ocean has been limited to regional studies. Microbial communities represent in-situ biosensors that are sensitive to changes in the surface ocean. They can therefore be used to identify where subtle changes in the environment occur and to understand links between the ecology and surrounding environment. Here, we perform the largest study of microbial biodiversity in the Indian Ocean, using 505 DNA samples collected on GO-SHIP cruises I07N and I09N. This dataset spans a large geographic area, starting in the southern Indian Ocean gyre, crossing through the equatorial zone, and entering the Arabian Sea or the Bay of Bengal. We used 16S rRNA amplicon sequencing to identify transition points in bacterial community structure and to define ecological boundaries. We found that these boundaries aligned with shifts in geochemistry (e.g., nutrient availability) and/or physical dynamics (e.g., ocean fronts, eddies, and salinity), indicating fine-scale regional separation in biogeochemical functioning. Thus, our study demonstrates how using microbial communities provides an integrated approach for evaluating links between the ecology, geochemistry, and physical dynamics of the Indian Ocean.</p>

NAPTRAM - Plastiktransportmechanismen, Senken und Interaktionen mit Biota im Nordatlantik / NAPTRAM - North Atlantic plastic transport mechanisms, sinks, and interactions with biota, Cruise No. SO279, Emden (Germany) – Emden (Germany), 04.12.2020 – 05.01.2021

The coastal and open oceans represent a major, but yet unconstrained, sink for plastics. It is likely that plastic-biota interactions are a key driver for the fragmentation, aggregation, and vertical transport of plastic litter from surface waters to sedimentary sinks. Cruise SO279 conducted sampling to address core questions of microplastic distribution in the open ocean water column, biota, and sediments. Seven stations were sampled between the outer Bay of Biscay and the primary working area south of the Azores. Additional samples were collected from surface waters along the cruise track to link European coastal and shelf waters with the open ocean gyre. Microplastic samples coupled with geochemical tracer analyses will build a mechanistic understanding of MP transport and its biological impact reaching from coastal seas to the central gyre water column and sinks at the seabed. Furthermore, floating plastics were sampled for microbial community and genetic analyses to investigate potential enzymatic degradation pathways. Cruise SO279 served as the third cruise of a number of connected research cruises to build an understanding of the transport pathways of plastic and microplastic debris in the North Atlantic from the input through rivers and air across coastal seas into the accumulation spots in the North Atlantic gyre and the vertical export to its sink at the seabed. The cruise was an international effort as part of the JPI Oceans project HOTMIC (“HOrizontal and vertical oceanic distribution, Transport, and impact of MICroplastics”) and the BMBF funded project PLASTISEA (‘Harvesting the marine Plastisphere for novel cleaning concepts’), and formed a joint effort of HOTMIC and PLASTISEA researchers from a range of countries and institutes.

The Role of Changing Indian Ocean Salinity in shaping Pleistocene Climate

<p>Indian Ocean surface salinity dynamics are thought to play an important role in shaping glacial-interglacial climate through controlling Agulhas leakage efficiency. It is proposed that a strong Agulhas leakage supplies warm and salty Indian ocean surface waters to Atlantic surface currents influencing convective potential at North Atlantic deep-water formation sites. Here, we present new planktonic foraminiferal Mg/Ca and stable isotope-derived salinity reconstructions for the last 1.2Ma from the northern Mozambique channel. We find salinity increases well before terminations, followed by early decrease before glacial inception. We present a possible link between the hydrography in the northern Mozambique channel and whole ocean salinity changes due to unique surface circulation in the Indian ocean. Despite being a mostly tropical and subtropical ocean, salinity in the modern tropical Indian Ocean is fresher than at comparable latitudes in the Atlantic or Pacific. This is due to the inflow of freshwater from the Indonesian throughflow and recycling via an active Agulhas leakage. We show that salinity in the glacial western Indian Ocean was significantly higher due to a reduced ITF and a weaker Agulhas leakage. We hypothesise that opening and closing of these two gateways influences the development/diminishment of a strong subtropical Indian Ocean gyre which controls sea surface salinity and temperature of tropical Indian Ocean water masses and subsequently the efficiency of the Agulhas Leakage.</p>

A Parasitic Arsenic Cycle That Shuttles Energy from Phytoplankton to Heterotrophic Bacterioplankton

ABSTRACTIn many regions of the world oceans, phytoplankton face the problem of discriminating between phosphate, an essential nutrient, and arsenate, a toxic analogue. Many phytoplankton, including the most abundant phytoplankton group known,Prochlorococcus, detoxify arsenate (AsV) by reduction to arsenite (AsIII), followed by methylation and excretion of the methylated arsenic products. We synthesized [14C]dimethyl arsenate (DMA) and used it to show that culturedPelagibacterstrain HTCC7211 (SAR11) cells oxidize the methyl group carbons of DMA, producing14CO2and ATP. We measured [14C]DMA oxidation rates in the P-depleted surface waters of the Sargasso Sea, a subtropical ocean gyre. [14C]DMA was oxidized to14CO2by Sargasso Sea plankton communities at a rate that would cause turnover of the estimated DMA standing stock every 8.1 days. SAR11 strain HTCC7211, which was isolated from the Sargasso Sea, has a pair of arsenate resistance genes and was resistant to arsenate, showing no growth inhibition at As/P ratios of >65:1. Across the global oceans, there was a strong inverse relationship between the frequency of the arsenate reductase (LMWPc_ArsC) inPelagibactergenomes and phosphate concentrations. We propose that the demethylation of methylated arsenic compounds byPelagibacterand possibly other bacterioplankton, coupled with arsenate resistance, results in the transfer of energy from phytoplankton to bacteria. We dub this a parasitic cycle because the release of arsenate byPelagibacterin principle creates a positive-feedback loop that forces phytoplankton to continually regenerate arsenate detoxification products, producing a flow of energy to P-limited ocean regions.IMPORTANCEIn vast, warm regions of the oceans, phytoplankton face the problem of arsenic poisoning. Arsenate is toxic because it is chemically similar to phosphate, a scarce nutrient that phytoplankton cells need for growth. Many phytoplankton, including the commonest phytoplankton type in warm oceans,Prochlorococcus, detoxify arsenate by adding methyl groups. Here we show that the most abundant non-photosynthetic plankton in the oceans, SAR11 bacteria, remove the methyl groups, releasing poisonous forms of arsenic back into the water. We postulate that the methylation and demethylation of arsenic compounds creates a cycle in which the phytoplankton can never get ahead and must continually transfer energy to the SAR11 bacteria. We dub this a parasitic process and suggest that it might help explain why SAR11 bacteria are so successful, surpassing all other plankton in their numbers. Field experiments were done in the Sargasso Sea, a subtropical ocean gyre that is sometimes called an ocean desert because, throughout much of the year, there is not enough phosphorous in the water to support large blooms of phytoplankton. Ocean deserts are expanding as the oceans absorb heat and grow warmer.