Biology subjects

Berman-Frank, I.

Publications and source records attributed to Berman-Frank, I..

6 recordsLinked to original sources

bioRxiv2024

Interannual changes in nutrient and phytoplankton dynamics in the Eastern Mediterranean Sea (EMS) predict the consequences of climate change; results from the Sdot-Yam Time-series station 2018-2022

Global climate change is predicted to reduce nutrient fluxes into the photic zone, particularly in tropical and subtropical ocean gyres, while the occasional major storms will result in increased nutrient pulses. In this study the nutrient and phytoplankton dynamics have been determined at a new time-series station in the southeastern Levantine basin of the Eastern Mediterranean Sea (EMS) over 4.5 years (2017-2022). In 2018 and 2019, there was a moderate concentration of residual nitrate and nitrite (N+N) in the photic zone (280-410nM) in winter, resulting in phytoplankton dynamics dominated by cyanobacteria with relatively few picoeukaryotes (280{+/-} 90 gC m-2). Winter storm driven mixing was much reduced in 2020 and particularly in 2021, resulting in a lower concentration of N+N in the photic zone, which decreased during summer stratification, such that by August 2021, the N+N was highly depleted (<60 nM) resulting in an integrated phytoplankton biomass of 23 gC m-2. A major storm in December 2021 (Storm Carmel) injected high N+N (750 nM; max = 1090 nM) in the upper 100 m, which stimulated pico and nanophytoplankton biomass ([~]2400 gC m-2) and probably increased eukaryotes (diatoms). The pattern of measured silica reinforced our conclusion that we sampled 3 different nutrient and ecosystem states. Phosphate was always at or close to LoD because of rapid uptake by cyanobacteria into their periplasm. These results predict that climate change in the EMS will result in periods of nutrient and phytoplankton depletion (Famine) interrupted by short periods of Mesotrophy (Feast) caused by major storms. Highlights- Nutrient dynamics from 4 years of Time-series station in the S.E. Levantine basin - Defined ecosystem status of normal, depleted and temporarily mesotrophic which are predicted status caused by climate change - Winters with low deep mixing resulted in severely nutrient depleted conditions subsequently - Major storm and relatively shallow nutricline resulted in temporary mesotrophic status

ecology↗

bioRxiv2022

Metagenomes of Red Sea subpopulations challenge the use of morphology and marker genes to assess Trichodesmium diversity

The bloom forming Trichodesmium are filamentous cyanobacteria of key interest due to their ability to fix carbon and nitrogen within an oligotrophic marine environment. Trichodesmium blooms typically comprise a complex assemblage of subpopulations and colony-morphologies that are predicted to exhibit distinct ecological lifestyles. Here, we assessed the poorly studied diversity of Trichodesmium in the Red Sea, based on metagenome-assembled genomes (MAGs) and hetR gene-based phylotyping. We assembled four non-redundant MAGs from morphologically distinct Trichodesmium colonies (tufts, dense and thin puffs). T. thiebautii (puffs) and T. erythraeum (tufts) were the dominant species within these morphotypes. While subspecies diversity is present for both T. thiebautii and T. erythraeum, a single T. thiebautii genotype comprised both thin and dense puff morphotypes, and we therefore hypothesize that the phenotypic variation between these morphologies is likely attributed to gene regulation. Additionally, we found the rare non-diazotrophic clade IV and V genotypes, related to T. nobis and T. miru respectively, that likely occurred as single filaments. HetR gene phylogeny indicates that the genotype in clade IV could represent the species T. contortum. We further show that hetR phylotyping can overestimate the taxonomic diversity of Trichodesmium, as two copies of the hetR gene were present within T. thiebautii genomes, one of which misidentified this lineage as T. aureum. Taken together, our results highlight the importance of re-assessing Trichodesmium taxonomy while showing the ability of genomics to capture the complex diversity and distribution of Trichodesmium populations.

microbiology↗

bioRxiv2022

Trichodesmium Erythraeum produces a higher photocurrent than other cyanobacterial species in bio-photo electrochemical cells.

In recent years, the increase in world energy consumption, and the worries from potential future disasters that may derive from climate change have inspired the motivation to develop renewable energy technologies. One of the promising methods is the utilization of whole bacterial cells to produce photocurrent in a bio-photo electrochemical cell (BPEC). The photocurrent derives from the photosynthesis pathway, while the redox couple NADP+/NADPH perform cyclic electron mediation between photosystem I inside the cells, and the anode. Over the years, various cyanobacterial species were utilized in diverse BPECs setups, while the photocurrent was enhanced by the addition of natural electron mediators such as NAD+, NADP+, Cytochrome C, Vitamin B1, and the artificial mediator potassium ferricyanide. The cyanobacterium Trichodesmium Erythraeum (Te) is a marine species that consist of high content of Phycocyanin and Phycoerythrin pigments that play a major role in photosynthesis enhancement. In this work, we produce for the first-time photocurrent from Te. We apply 2D-fluorescence measurements to detect its NADPH secretion and show that its photocurrent production is enhanced as a function of increasing electrolyte salinity. Finally, we produce photocurrent from additional cyanobacterial species: Synechocystis sp. PCC6803, Synechococcus elongatus PCC 7942, Acaryochloris marina MBIC 11017, and Spirulina, using their cultivation medium as electrolytes in the BPEC. We show that TE produces a photocurrent intensity that is significantly greater than all other species with and without the addition of exogenous electron mediators. The utilization of TE may pave the way toward the establishment of marine clean energy technologies.

microbiology↗

bioRxiv2021

Massive export of diazotrophs across the tropical south Pacific Ocean

Diazotrophs are widespread microorganisms that alleviate nitrogen limitation in 60% of our oceans, regulating marine productivity. Yet, their contribution to organic matter export has not been quantified, making an assessment of their impact on the biological carbon pump impossible. Here, we demonstrate that cyanobacterial and non-cyanobacterial diazotrophs are massively exported down to 1000 m-depth in the western subtropical South Pacific Ocean (WTSP), accounting for up to 52-100% of the total particulate nitrogen export fluxes. We further demonstrate that small size unicellular diazotrophs (UCYN, 1-8 {micro}m) are exported more efficiently than filamentous diazotrophs (>100-1000 {micro}m) under the form of large (>50 {micro}m) aggregates linked by an extracellular organic matrix. Beyond the WTSP, our data are supported by analysis of the Tara Oceans metagenomes collected in other ocean basins, showing that diazotrophs are systematically detected in mesopelagic waters when present at the surface. We thus conclude that diazotrophs are key players in carbon sequestration in the ocean and need to be considered in future studies to improve the accuracy of current regional and global estimates of export.

microbiology↗

bioRxiv2021

Seasonal dynamics of phytoplankton and bacterioplankton at the ultra-oligotrophic southeastern Mediterranean Sea

The Eastern Mediterranean Sea (EMS) is a poorly studied ultra-oligotrophic marine environment, dominated by small-size phyto- and bacterioplankton. Here, we describe the dynamics of a single annual cycle (2018-19) of phyto- and bacterioplankton (abundances, pigments and productivity) in relation to the physical and chemical conditions in the photic water column at an offshore EMS site (Station THEMO-2, [~]1,500m depth, 50km offshore). We show that phytoplankton biomass (as chlorophyll a), primary and bacterial productivity differed between the mixed winter (January-April) and the thermally stratified (May-December) periods. Prochlorococcus and Synechococcus numerically dominated the picophytoplankton populations, with each clade revealing different temporal and depth changes indicative to them, while pico-eukaryotes (primarily haptophytes) were less abundant, yet likely contributed significant biomass. Estimated primary productivity ([~]32 gC m-2 y-1) was lower compared with other well-studied oligotrophic locations, including the north Atlantic and Pacific (BATS and HOT observatories), the western Mediterranean (DYFAMED observatory) and the Red Sea, and was on-par with the ultra-oligotrophic South Pacific Gyre. In contrast, integrated bacterial production ([~]11 gC m-2 y-1) was similar to other oligotrophic locations. Phytoplankton seasonal dynamics were similar to those at BATS and the Red Sea, suggesting an observable effect of winter mixing in this ultra-oligotrophic location. These results highlight the ultra-oligotrophic conditions in the EMS and provide, for the first time in this region, a full-year baseline and context to ocean observatories in the region. HighlightsO_LIBacterioplankton dynamics were assessed monthly in the Eastern Mediterranean Sea C_LIO_LISmall-sized picophytoplankton numerically dominated the phytoplankton community C_LIO_LISeasonal phytoplankton dynamics are similar to BATS and Red Sea, but not to HOT C_LIO_LIAnnual primary productivity is among the lowest in the worlds oceans C_LIO_LIBacterial to primary production ratio is higher than most oligotrophic seas C_LI

microbiology↗

bioRxiv2020

Fine scale sampling unveils diazotroph patchiness in the South Pacific Ocean

Diazotrophs are important contributors to reactive nitrogen availability in the ocean. Oceanographic cruise data accumulated along decades has revealed a heterogeneous distribution of diazotroph species at regional to global scales. However, the role of dynamic fine scale structures in distributing diazotrophs is not well understood. This is due to typical insufficient spatiotemporal resolution sampling and the lack of detailed physical studies in parallel. Here we show the distribution of five groups of diazotrophs in the South Pacific at an unprecedented resolution of 7-16 km. We find a patchy distribution of diazotrophs, with each group being differently affected by parameters describing fine scale structures. The observed variability could not have been revealed with a lower resolution sampling, highlighting the need to consider fine scale physics to resolve the distribution of diazotrophs in the ocean.

microbiology↗