Natural attenuation of oil in marine environments: A review.

Natural attenuation is an important process for oil spill management in marine environments. Natural attenuation affects the fate of oil by physical, chemical, and biological processes, which include evaporation, dispersion, dissolution, photo-oxidation, emulsification, oil particle aggregation, and biodegradation. This review examines the cumulative knowledge regarding these natural attenuation processes as well as their simulation and prediction using modelling approaches. An in-depth discussion is provided on how oil type, microbial community and environmental factors contribute to the biodegradation process. It describes how our understanding of the structure and function of indigenous oil degrading microbial communities in the marine environment has been advanced by the application of next generation sequencing tools. The synergetic and/or antagonist effects of oil spill countermeasures such as the application of chemical dispersants, in-situ burning and nutrient enrichment on natural attenuation were explored. Several knowledge gaps were identified regarding the synergetic and/or antagonistic effects of active response countermeasures on the natural attenuation/biodegradation process. This review highlighted the need for field data on both the effectiveness and potential detrimental effects of oil spill response options to support modelling and decision-making on their selection and application.

Draft Whole-Genome Sequences of the Polar Cyanobacterium Leptolyngbya sp. Strain Cla-17 and Its Associated Flavobacterium.

Draft whole-genome sequences of a coculture are presented. One component was a polar cyanobacterium, Leptolyngbya sp. strain Cla-17. The second was a heterotrophic bacterium, Flavobacterium saccharophilum, found in the phycosphere of the cyanobacterium.

Binary toxicity of polystyrene nanoplastics and polybrominated diphenyl ethers to Arctic Cyanobacteria under ambient and future climates.

Cyanobacteria are the predominant biota in the Arctic. Interactive effects on Arctic cyanobacteria between climate-change-shifting parameters and anthropogenic contaminants are largely unknown. We utilized a fractional factorial experiment and Arctic cyanobacteria Pseudanabaena biceps Strain PCCC_O-153 to capture the complexity of interacting climate factors, nano-polystyrene (nano-PS) and 2,2´,4,4´-tetrabromodipenyl ether (BDE-47). The short-term binary toxicity of nano-PS and BDE-47 was then examined through experiments, toxicity units, and reference models. The toxic mechanism was further revealed through biochemical analyses and multivariate statistics. We found that BDE-47 and nano-PS had more hazardous effects than changing climate conditions. The mixture had antagonistic effects on PCCC_O-153, attributing to the aggregation of nano-PS, the adsorption of BDE-47, and the wrapping of both contaminants by released extracellular polymeric substances. Binary toxicity was caused by the chain reactions triggered by combining individual contaminants. Total protein was a sensitive target and positively correlated to chlorophyll pigment. Oxidative stress for the mixture mainly resulted from the presence of nano-PS. This is the first study to access the hazardous effects of a mixture of anthropogenic contaminants on Arctic cyanobacteria under ambient and future climates.

Deep ocean microbial communities produce more stable dissolved organic matter through the succession of rare prokaryotes.

The microbial carbon pump (MCP) hypothesis suggests that successive transformation of labile dissolved organic carbon (DOC) by prokaryotes produces refractory DOC (RDOC) and contributes to the long-term stability of the deep ocean DOC reservoir. We tested the MCP by exposing surface water from a deep convective region of the ocean to epipelagic, mesopelagic, and bathypelagic prokaryotic communities and tracked changes in dissolved organic matter concentration, composition, and prokaryotic taxa over time. Prokaryotic taxa from the deep ocean were more efficient at consuming DOC and producing RDOC as evidenced by greater abundance of highly oxygenated molecules and fluorescent components associated with recalcitrant molecules. This first empirical evidence of the MCP in natural waters shows that carbon sequestration is more efficient in deeper waters and suggests that the higher diversity of prokaryotes from the rare biosphere holds a greater metabolic potential in creating these stable dissolved organic compounds.

Cryptic sex in the smallest eukaryotic marine green alga.

Ostreococcus spp. are common worldwide oceanic picoeukaryotic pelagic algae. The complete genomes of three strains from different ecological niches revealed them to represent biologically distinct species despite their identical cellular morphologies (cryptic species). Their tiny genomes (13 Mb), with approximately 20 chromosomes, are colinear and densely packed with coding sequences, but no sexual life cycle has been described. Seventeen new strains of one of these species, Ostreococcus tauri, were isolated from 98 seawater samplings from the NW Mediterranean by filtering, culturing, cloning, and plating for single colonies and identification by sequencing their ribosomal 18S gene. In order to find the genetic markers for detection of polymorphisms and sexual recombination, we used an in silico approach to screen available genomic data. Intergenic regions of DNA likely to evolve neutrally were analyzed following polymerase chain reaction amplification of sequences using flanking primers from adjacent conserved coding sequences that were present as syntenic pairs in two different species of Ostreococcus. Analyses of such DNA regions from eight marker loci on two chromosomes from each strain revealed that the isolated O. tauri clones were haploid and that the overall level of polymorphism was approximately 0.01. Four different genetic tests for recombination showed that sexual exchanges must be inferred to account for the between-locus and between-chromosome marker combinations observed. However, our data suggest that sexual encounters are infrequent because we estimate the frequency of meioses/mitoses among the sampled strains to be 10(-6). Ostreococcus tauri and related species encode and express core genes for mitosis and meiosis, but their mechanisms of cell division and recombination, nevertheless, remain enigmatic because a classical eukaryotic spindle with 40 canonical microtubules would be much too large for the available approximately 0.9-microm(3) cellular volume.

Draft Whole-Genome Sequence of the Alkane-Synthesizing Polar Cyanobacterium Pseudanabaena biceps Strain O-153.

Alkane biosynthesis by polar cyanobacteria has not yet been reported. We present here the draft whole-genome sequence of an alkane-synthesizing polar cyanobacterium, Pseudanabaena biceps strain O-153. The genes coding for the two key enzymes involved in the alkane biosynthetic pathway were found contiguously in the genome.

Potential for Local Fertilization: A Benthocosm Test of Long-Term and Short-Term Effects of Mussel Excretion on the Plankton.

Mussel aquaculture has expanded worldwide and it is important to assess its impact on the water column and the planktonic food web to determine the sustainability of farming practices. Mussel farming may affect the planktonic food web indirectly by excreting bioavailable nutrients in the water column (a short-term effect) or by increasing nutrient effluxes from biodeposit-enriched sediments (a long-term effect). We tested both of these indirect effects in a lagoon by using plankton-enclosing benthocosms that were placed on the bottom of a shallow lagoon either inside of a mussel farm or at reference sites with no history of aquaculture. At each site, half of the benthocosms were enriched with seawater that had held mussels (excretion treatment), the other half received non-enriched seawater as a control treatment. We monitored nutrients ([PO43-] and [NH4+]), dissolved oxygen and plankton components (bacteria, the phytoplankton and the zooplankton) over 5 days. We found a significant relationship between long-term accumulation of mussel biodeposits in sediments, water-column nutrient concentrations and plankton growth. Effects of mussel excretion were not detected, too weak to be significant given the spatial and temporal variability observed in the lagoon. Effects of mussels on the water column are thus likely to be coupled to benthic processes in such semi-enclosed water bodies.

High-throughput sequencing: a roadmap toward community ecology.

High-throughput sequencing is becoming increasingly important in microbial ecology, yet it is surprisingly under-used to generate or test biogeographic hypotheses. In this contribution, we highlight how adding these methods to the ecologist toolbox will allow the detection of new patterns, and will help our understanding of the structure and dynamics of diversity. Starting with a review of ecological questions that can be addressed, we move on to the technical and analytical issues that will benefit from an increased collaboration between different disciplines.

Morphology, genome plasticity, and phylogeny in the genus ostreococcus reveal a cryptic species, O. mediterraneus sp. nov. (Mamiellales, Mamiellophyceae).

Coastal marine waters in many regions worldwide support abundant populations of extremely small (1-3 µm diameter) unicellular eukaryotic green algae, dominant taxa including several species in the class Mamiellophyceae. Their diminutive size conceals surprising levels of genetic diversity and defies classical species' descriptions. We present a detailed analysis within the genus Ostreococcus and show that morphological characteristics cannot be used to describe diversity within this group. Karyotypic analyses of the best-characterized species O. tauri show it to carry two chromosomes that vary in size between individual clonal lines, probably an evolutionarily ancient feature that emerged before species' divergences within the Mamiellales. By using a culturing technique specifically adapted to members of the genus Ostreococcus, we purified >30 clonal lines of a new species, Ostreococcus mediterraneus sp. nov., previously known as Ostreococcus clade D, that has been overlooked in several studies based on PCR-amplification of genetic markers from environment-extracted DNA. Phylogenetic analyses of the S-adenosylmethionine synthetase gene, and of the complete small subunit ribosomal RNA gene, including detailed comparisons of predicted ITS2 (internal transcribed spacer 2) secondary structures, clearly support that this is a separate species. In addition, karyotypic analyses reveal that the chromosomal location of its ribosomal RNA gene cluster differs from other Ostreococcus clades.

Benthic cyanobacterial mats in the high arctic: multi-layer structure and fluorescence responses to osmotic stress.

Cyanobacterial mats are often a major biological component of extreme aquatic ecosystems, and in polar lakes and streams they may account for the dominant fraction of total ecosystem biomass and productivity. In this study we examined the vertical structure and physiology of Arctic microbial mats relative to the question of how these communities may respond to ongoing environmental change. The mats were sampled from Ward Hunt Lake (83°5.297'N, 74°9.985'W) at the northern coast of Arctic Canada, and were composed of three visibly distinct layers. Microsensor profiling showed that there were strong gradients in oxygen within each layer, with an overall decrease from 100% saturation at the mat surface to 0%, at the bottom, accompanied by an increase of 0.6 pH units down the profile. Gene clone libraries (16S rRNA) revealed the presence of Oscillatorian sequences throughout the mat, while Nostoc related species dominated the two upper layers, and Nostocales and Synechococcales sequences were common in the bottom layer. High performance liquid chromatography analyses showed a parallel gradient in pigments, from high concentrations of UV-screening scytonemin in the upper layer to increasing zeaxanthin and myxoxanthin in the bottom layer, and an overall shift from photoprotective to photosynthetic carotenoids down the profile. Climate change is likely to be accompanied by lake level fluctuations and evaporative concentration of salts, and thus increased osmotic stress of the littoral mat communities. To assess the cellular capacity to tolerate increasing osmolarity on physiology and cell membrane integrity, mat sections were exposed to a gradient of increasing salinities, and PAM measurements of in vivo chlorophyll fluorescence were made to assess changes in maximum quantum yield. The results showed that the mats were tolerant of up to a 46-fold increase in salinity. These features imply that cyanobacterial mats are resilient to ongoing climate change, and that in the absence of major biological perturbations, these vertically structured communities will continue to be a prominent feature of polar aquatic ecosystems.