Teamwork in the viscous oceanic microscale

Nutrient acquisition is crucial for oceanic microbes, and competitive solutions to solve this challenge have evolved among a range of unicellular protists. However, solitary solutions are not the only approach found in natural populations. A diverse array of oceanic protists form temporary or even long-lasting attachments to other protists and marine aggregates. Do these planktonic consortia provide benefits to their members? Here, we use empirical and modeling approaches to evaluate whether the relationship between a large centric diatom, Coscinodiscus wailesii, and a ciliate epibiont, Pseudovorticella coscinodisci, provides nutrient flux benefits to the host diatom. We find that fluid flows generated by ciliary beating can increase nutrient flux to a diatom cell surface four to 10 times that of a still cell without ciliate epibionts. This cosmopolitan species of diatom does not form consortia in all environments but frequently joins such consortia in nutrient-depleted waters. Our results demonstrate that symbiotic consortia provide a cooperative alternative of comparable or greater magnitude to sinking for enhancement of nutrient acquisition in challenging environments.

Bacterial diketopiperazines stimulate diatom growth and lipid accumulation

Diatoms are photosynthetic microalgae that fix a significant fraction of the world’s carbon. Because of their photosynthetic efficiency and high-lipid content, diatoms are priority candidates for biofuel production. Here, we report that sporulating Bacillus thuringiensis and other members of the Bacillus cereus group, when in co-culture with the marine diatom Phaeodactylum tricornutum, significantly increase diatom cell count. Bioassay-guided purification of the mother cell lysate of B. thuringiensis led to the identification of two diketopiperazines (DKPs) that both stimulate P. tricornutum growth and increase its lipid content. These findings may be exploited to enhance P. tricornutum growth and microalgae-based biofuel production. As increasing numbers of DKPs are isolated from marine microbes, the work gives potential clues to bacterial-produced growth factors for marine microalgae.

RNA-Seq and differential gene expression analysis in Temora stylifera copepod females with contrasting non-feeding nauplii survival rates: an environmental transcriptomics study

Background Copepods are fundamental components of pelagic food webs, but reports on how molecular responses link to reproductive success in natural populations are still scarce. We present a de novo transcriptome assembly and differential expression (DE) analysis in Temora stylifera females collected in the Gulf of Naples, Mediterranean Sea, where this copepod dominates the zooplankton community. High-Throughput RNA-Sequencing and DE analysis were performed from adult females collected on consecutive weeks (May 23rd and 30th 2017), because opposite naupliar survival rates were observed. We aimed at detecting key genes that may have influenced copepod reproductive potential in natural populations and whose expression was potentially affected by phytoplankton-derived oxylipins, lipoxygenase-derived products strongly impacting copepod naupliar survival. Results On the two sampling dates, temperature, salinity, pH and oxygen remained stable, while variations in phytoplankton cell concentration, oxylipin concentration and oxylipin-per-diatom-cell production were observed. T. stylifera naupliar survival was 25% on May 23rd and 93% on May 30th. De novo assembly generated 268,665 transcripts (isoforms) and 120,749 unique ‘Trinity predicted genes’ (unigenes), of which 50% were functionally annotated. Out of the 331 transcript isoforms differentially expressed between the two sampling dates, 119 sequences were functionally annotated (58 up- and 61 down-regulated). Among predicted genes (unigenes), 144 sequences were differentially expressed and 31 (6 up-regulated and 25 down-regulated) were functionally annotated. Most of the significantly down-regulated unigenes and isoforms were A5 Putative Odorant Binding Protein (Obp). Other differentially expressed sequences (isoforms and unigenes) related to developmental metabolic processes, protein ubiquitination, response to stress, oxidation-reduction reactions and hydrolase activities. DE analysis was validated through Real Time-quantitative PCR of 9 unigenes and 3 isoforms. Conclusions Differential expression of sequences involved in signal detection and transduction, cell differentiation and development offered a functional interpretation to the maternally-mediated low naupliar survival rates observed in samples collected on May 23rd. Down-regulation of A5 Obp along with higher quantities of oxylipins-per-litre and oxylipins-per-diatom-cell observed on May 23rd could suggest oxylipin-mediated impairment of naupliar survival in natural populations of T. stylifera. Our results may help identify biomarker genes explaining variations in copepod reproductive responses at a molecular level.

Arctic (Svalbard islands) active and exported diatom stocks and cell health status

Diatoms tend to dominate the Arctic spring phytoplankton bloom, a key event in the ecosystem including a rapid decline in surface-water pCO2. While a mass sedimentation event of diatoms at the bloom terminus is commonly observed, there are few reports on the status of diatoms' health during Arctic blooms and its possible role on sedimentary fluxes. Thus, we examine the idea that the major diatom-sinking event which occurs at the end of the regional bloom is driven by physiologically deteriorated cells. Here we quantify, using the Bottle-Net, Arctic diatom stocks below and above the photic zone and assess their cell health status. The communities were sampled around the Svalbard islands and encompassed pre- to post-bloom conditions. A mean of 24.2±6.7 % SE (standard error) of the total water column (max. 415 m) diatom standing stock was found below the photic zone, indicating significant diatom sedimentation. The fraction of living diatom cells in the photic zone averaged 59.4±6.3 % but showed the highest mean percentages (72.0 %) in stations supporting active blooms. In contrast, populations below the photic layer were dominated by dead cells (20.8±4.9 % living cells). The percentage of diatoms' standing stock found below the photic layer was negatively related to the percentage of living diatoms in the surface, indicating that healthy populations remained in the surface layer. Shipboard manipulation experiments demonstrated that (1) dead diatom cells sank faster than living cells, and (2) diatom cell mortality increased in darkness, showing an average half-life among diatom groups of 1.025±0.075 d. The results conform to a conceptual model where diatoms grow during the bloom until resources are depleted and supports a link between diatom cell health status (affected by multiple factors) and sedimentation fluxes in the Arctic. Healthy Arctic phytoplankton communities remained at the photic layer, whereas the physiologically compromised (e.g., dying) communities exported a large fraction of the biomass to the aphotic zone, fueling carbon sequestration to the mesopelagic and material to benthic ecosystems.

A phosphorescent iridium complex as a probe for diatom cells’ viability

ABSTRACTDiatoms are unicellular photosynthetic algae that autonomously fabricate a porous organized biosilica shell refined in billion years of evolution. They represent an inexhaustible source of low cost, biocompatible mesoporous silica. Despite the major advances in the genomic field, studies on diatom cell biology are still hampered by a lack of cellular tools. In particular, cell staining assays of diatoms viability are still limited or not well performant. Here we provide a phosphorescent organometallic iridium complex (Ir-Fcx) suitable to act as staining agent to detect diatoms viability.

KARAKTERISTIK UMUM DIATOM DAN APLIKASINYA PADA BIDANG GEOSAINS

AN OVERVIEW OF DIATOM AND ITS APPLICATIONS ON THE GEOSCIENCE AREA. Diatoms have been being studied in many countries. Diatoms provide a valuable and well-understood means on biomonitoring – one of which is focused on the base of the aquatic foodweb and highly representative of water quality. They are found in most aquatic environments and the sys tematic and taxonomic investigations of modern and fossil diatoms have been supported by numerous stud ies of distributional ecology. Diatom systematics, taxonomy and ecology indeed offer a wide scope of applications - from water quality to environmental monitoring and biostratigraphy as well as on geoscience area. The application of diatom analysis in determining whether drowning was the cause of death has proven to be a valuable tool in forensic science. Furthermore, diatoms can provide a record of environmental conditions because their relationship to water quality and aquatic habitat has been already known, and the diatom cell wall, which is silicified to form a frustule, is well-preserved, easily detectable and occurs in high numbers in sediment and water. However, this should not be limited to simply make an inventory of data: thoughtful ecology and paleo-ecology will assist in predicting the environmental impact of pollution and climate changes.

The role of the diatom cell form in the competition for light energy

We proposed a new parameter regulating distribution of the species – the daily average absorbed energy of PAR by a unit of phytoplankton cell volume, determined by the shape, size and concentration of pigments. We calculated this parameter for some dominant diatom species of the northeastern part of the Black Sea and normalize it by the average daily PAR for periods of dominance. We established that for species successfully compete for an ecological niche this parameter should be approximately at the same level in different seasons.

Diversity and distribution of diatoms in Bagmati River, Kathmandu, Nepal

Diversity and distribution of diatoms in different seasons from different localities and habitats of Bagmati River, Kathmandu was studied. Samples were collected as epilithic forms using a toothbrush, epipelic forms using a dropper, and epiphytic forms by squeezing aquatic macrophytes and were preserved in FAA solution. The dominant diatom taxa of Bagmati river were Achnanthes crenulata, Gomphonema pseudoaugur, Nitzschia linearis, N. palea, Pinnularia cf divergens and Surirella linearis. Out of 48 taxa reported, maximum taxa (87.5%) were found at Mulkharka site whereas taxa were minimum (39.58%) at Pashupati-Guheshwori site. The sizes of diatom cell, from largest to smallest, also followed the same pattern as above. Ten diatom taxa were common in all three sites. Seasonal and habitat diversity of diatom studied in Mulkharka site showed that the maximum number of taxa was reported during summer (92.85%) and least during winter (23.8%), and maximum taxa were found as epilithic (85.71%) followed by epipelic (38.09%) and epiphytic (33.33%).