Plastic garbage patches at the ocean surface are symptomatic of a wider pollution affecting the whole marine environment. Sinking of plastic debris increasingly appears to be an important process in ...the global fate of plastic in the ocean. However, there is insufficient knowledge about the processes affecting plastic distributions and degradation and how this influences the release of additives under varying environmental conditions, especially in deep-sea environments. Here we show that in abiotic conditions increasing hydrostatic pressure inhibits the leaching of the heaviest organic additives such as tris(2-ethylhexyl) phosphate and diisononyl phthalate from polyethylene and polyvinylchloride materials, whereas deep-sea and surface marine prokaryotes promote the release of all targeted additives (phthalates, bisphenols, organophosphate esters). This study provides empirical evidences for more efficient additive release at the ocean surface than in deep seawater, where the major plastic burden is supposed to transit through before reaching the sediment compartment.
Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean. The rate at which the sinking carbon is ...converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink.
Around 30 species of marine bacteria can emit light, a critical characteristic in the oceanic environment is mostly deprived of sunlight. In this article, we first review current knowledge on ...bioluminescent bacteria symbiosis in light organs. Then, focusing on gut-associated bacteria, we highlight that recent works, based on omics methods, confirm previous claims about the prominence of bioluminescent bacterial species in fish guts. Such host–symbiont relationships are relatively well-established and represent important knowledge in the bioluminescence field. However, the consequences of bioluminescent bacteria continuously released from light organs and through the digestive tracts to the seawater have been barely taken into account at the ecological and biogeochemical level. For too long neglected, we propose considering the role of bioluminescent bacteria and reconsidering the biological carbon pump, taking into account the bioluminescence effect (“bioluminescence shunt hypothesis”). Indeed, it has been shown that marine snow and fecal pellets are often luminous due to microbial colonization, which makes them a visual target. These luminous particles seem preferentially consumed by organisms of higher trophic levels in comparison to nonluminous ones. As a consequence, the sinking rate of consumed particles could be either increased (due to repackaging) or reduced (due to sloppy feeding or coprophagy/coprorhexy), which can imply a major impact on global biological carbon fluxes. Finally, we propose a strategy, at a worldwide scale, relying on recently developed instrumentation and methodological tools to quantify the impact of bioluminescent bacteria in the biological carbon pump.
Viruses are the most abundant biological organisms of the world's oceans. Viral infections are a substantial source of mortality in a range of organisms-including autotrophic and heterotrophic ...plankton-but their impact on the deep ocean and benthic biosphere is completely unknown. Here we report that viral production in deep-sea benthic ecosystems worldwide is extremely high, and that viral infections are responsible for the abatement of 80% of prokaryotic heterotrophic production. Virus-induced prokaryotic mortality increases with increasing water depth, and beneath a depth of 1,000 m nearly all of the prokaryotic heterotrophic production is transformed into organic detritus. The viral shunt, releasing on a global scale approximately 0.37-0.63 gigatonnes of carbon per year, is an essential source of labile organic detritus in the deep-sea ecosystems. This process sustains a high prokaryotic biomass and provides an important contribution to prokaryotic metabolism, allowing the system to cope with the severe organic resource limitation of deep-sea ecosystems. Our results indicate that viruses have an important role in global biogeochemical cycles, in deep-sea metabolism and the overall functioning of the largest ecosystem of our biosphere.
The pelagic realm of the dark ocean is characterized by high hydrostatic pressure, low temperature, high-inorganic nutrients, and low organic carbon concentrations. Measurements of metabolic ...activities of bathypelagic bacteria are often underestimated due to the technological limitations in recovering samples and maintaining them under
environmental conditions. Moreover, most of the pressure-retaining samplers, developed by a number of different labs, able to maintain seawater samples at
pressure during recovery have remained at the prototype stage, and therefore not available to the scientific community. In this paper, we will describe a ready-to-use pressure-retaining sampler, which can be adapted to use on a CTD-carousel sampler. As well as being able to recover samples under
high pressure (up to 60 MPa) we propose a sample processing in equi-pressure mode. Using a piloted pressure generator, we present how to perform sub-sampling and transfer of samples in equi-pressure mode to obtain replicates and perform hyperbaric experiments safely and efficiently (with <2% pressure variability). As proof of concept, we describe a field application (prokaryotic activity measurements and incubation experiment) with samples collected at 3,000m-depth in the Mediterranean Sea. Sampling, sub-sampling, transfer, and incubations were performed under
high pressure conditions and compared to those performed following decompression and incubation at atmospheric pressure. Three successive incubations were made for each condition using direct dissolved-oxygen concentration measurements to determine the incubation times. Subsamples were collected at the end of each incubation to monitor the prokaryotic diversity, using 16S-rDNA/rRNA high-throughput sequencing. Our results demonstrated that oxygen consumption by prokaryotes is always higher under
conditions than after decompression and incubation at atmospheric pressure. In addition, over time, the variations in the prokaryotic community composition and structure are seen to be driven by the different experimental conditions. Finally, within samples maintained under
high pressure conditions, the active (16S rRNA) prokaryotic community was dominated by sequences affiliated with rare families containing piezophilic isolates, such as Oceanospirillaceae or Colwelliaceae. These results demonstrate the biological importance of maintaining
conditions during and after sampling in deep-sea environments.
Summary
Effects of hydrostatic pressure on pure cultures of prokaryotes have been studied extensively but impacts at the community level in the ocean are less well defined. Here we consider ...hydrostatic pressure effects on natural communities containing both unadapted (piezosensitive) prokaryotes originating from surface water and adapted (including piezophilic) prokaryotes from the deep sea. Results from experiments mimicking pressure changes experienced by particle‐associated prokaryotes during their descent through the water column show that rates of degradation of organic matter (OM) by surface‐originating microorganisms decrease with sinking. Analysis of a much larger data set shows that, under stratified conditions, deep‐sea communities adapt to in situ conditions of high pressure, low temperature and low OM. Measurements made using decompressed samples and atmospheric pressure thus underestimate in situ activity. Exceptions leading to overestimates can be attributed to deep mixing events, large influxes of surface particles, or provision of excessive OM during experimentation. The sediment–water interface, where sinking particles accumulate, will be populated by a mixture of piezosensitive, piezotolerant and piezophilic prokaryotes, with piezophilic activity prevailing deeper within sediment. A schematic representation of how pressure shapes prokaryotic communities in the ocean is provided, allowing a reasonably accurate interpretation of the available activity measurements.
Bacterial-bioluminescence regulation is often associated with quorum sensing. Indeed, many studies have been made on this subject and indicate that the expression of the light-emission-involved genes ...is density dependent. However, most of these studies have concerned two model species,
and
. Very few works have been done on bioluminescence regulation for the other bacterial genera. Yet, according to the large variety of habitats of luminous marine bacteria, it would not be surprising to find different light-regulation systems. In this study, we used
ANT-2200, a piezophilic bioluminescent strain isolated from Mediterranean deep-sea waters (2200-m depth). To answer the question of whether or not the bioluminescence of
ANT-2200 is under quorum-sensing control, we focused on the correlation between growth and light emission through physiological, genomic and, transcriptomic approaches. Unlike
and
, the light of
ANT-2200 immediately increases from its initial level. Interestingly, the emitted light increases at much higher rate at the low cell density than it does for higher cell-density values. The expression level of the light-emission-involved genes stays constant all along the exponential growth phase. We also showed that, even when more light is produced, when the strain is cultivated at high hydrostatic pressure, no change in the transcription level of these genes can be detected. Through different experiments and approaches, our results clearly indicate that, under the tested conditions, the genes, directly involved in the bioluminescence in
ANT-2200, are not controlled at a transcriptomic level. Quite obviously, these results demonstrate that the light emission of the strain is not density dependent, which means not under quorum-sensing control. Through this study, we point out that bacterial-bioluminescence regulation should not, from now on, be always linked with the quorum-sensing control.
RNA-seq was used to study the response of Desulfovibrio hydrothermalis, isolated from a deep-sea hydrothermal chimney on the East-Pacific Rise at a depth of 2,600 m, to various hydrostatic pressure ...growth conditions. The transcriptomic datasets obtained after growth at 26, 10 and 0.1 MPa identified only 65 differentially expressed genes that were distributed among four main categories: aromatic amino acid and glutamate metabolisms, energy metabolism, signal transduction, and unknown function. The gene expression patterns suggest that D. hydrothermalis uses at least three different adaptation mechanisms, according to a hydrostatic pressure threshold (HPt) that was estimated to be above 10 MPa. Both glutamate and energy metabolism were found to play crucial roles in these mechanisms. Quantitation of the glutamate levels in cells revealed its accumulation at high hydrostatic pressure, suggesting its role as a piezolyte. ATP measurements showed that the energy metabolism of this bacterium is optimized for deep-sea life conditions. This study provides new insights into the molecular mechanisms linked to hydrostatic pressure adaptation in sulfate-reducing bacteria.
Carbon budgets of hydrothermal plumes result from the balance between carbon sinks through plume chemoautotrophic processes and carbon release via microbial respiration. However, the lack of ...comprehensive analysis of the metabolic processes and biomass production rates hinders an accurate estimate of their contribution to the deep ocean carbon cycle. Here, we use a biogeochemical model to estimate the autotrophic and heterotrophic production rates of microbial communities in hydrothermal plumes and validate it with in situ data. We show how substrate limitation might prevent net chemolithoautotrophic production in hydrothermal plumes. Elevated prokaryotic heterotrophic production rates (up to 0.9 gCm
y
) compared to the surrounding seawater could lead to 0.05 GtCy
of C-biomass produced through chemoorganotrophy within hydrothermal plumes, similar to the Particulate Organic Carbon (POC) export fluxes reported in the deep ocean. We conclude that hydrothermal plumes must be accounted for as significant deep sources of POC in ocean carbon budgets.
This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth >1000
m). Abundance, production and respiration of prokaryotes reflect supplies ...of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further testing on the validity of conversion factors.
Archaea, especially marine
Crenarchaeota Group I, are abundant in deep waters where they can fix dissolved inorganic carbon. Viruses appear to be important in the microbial loop in deep waters, displaying remarkably high virus to prokaryote abundance ratios in some oceanic regions. Sequencing of 18S rRNA genes revealed a tremendous diversity of small-sized protists in bathypelagic waters. Abundances of heterotrophic nanoflagellates (HNF) and ciliates decrease with depth more steeply than prokaryotes; nonetheless, data indicated that HNF consumed half of prokaryote production in the bathypelagic zone. Aggregates are important habitats for deep-water microbes, which produce more extracellular enzymes (on a per-cell basis) than surface communities. The theory of marine gel formation provides a framework to unravel complex interactions between microbes and organic polymers. Recent data on the effects of hydrostatic pressure on microbial activities indicate that bathypelagic microbial activity is generally higher under
in situ pressure conditions than at atmospheric pressures. High-throughput sequencing of 16S rRNA genes revealed a remarkable diversity of
Bacteria in the bathypelagic ocean. Metagenomics and comparative genomics of piezophiles reveal not only the high diversity of deep sea microbes but also specific functional attributes of these piezophilic microbes, interpreted as an adaptation to the deep water environment. Taken together, the data compiled on bathypelagic microbes indicate that, despite high-pressure and low-temperature conditions, microbes in the bathypelagic ocean dynamically interact with complex mixtures of organic matter, responding to changes in the ocean’s biogeochemical state.
PDF
