PhD Title: Programmed cell death in cyanobacteria
My research focuses on the factors which regulate programmed cell death (PCD) in cyanobacteria. Specifically, I study PCD in the marine cyanobacteria Trichodesmium which form extensive blooms in the tropical and subtropical surface-oceans. Trichodesmium undergoes an autocatalytic, genetically programmed cell death in response to environmental stressors such as high irradiance and Fe limitation. They have key enzymes of the eukaryotic PCD and several proteins from the metacaspase family. I study the role of PCD in blooms and cell death mechanism in Trichodesmium. My work involves both laboratory experiments with Trichodesmium cultures, and field experiments with natural Trichodesmium blooms. Molecular and physiological approaches are applied to examine expression of PCD in Trichodesmium at both the genetic and protein levels.
Trichodesmium bloom in the South West Pacific Ocean (New Caledonia).
Photo by D. Spungin
PhD Title: Trichomes to blooms in the marine diazotrophic cyanobacterium – Trichodesmium
Trichodesmium is a filamentous, non-heterocystous cyanobacteria whose filaments (trichomes) are composed of 10-100s of cells with similar morphologies. Trichomes can be found as single filaments, spherical (“puffs”) or fusiform (“tufts”) colonies . The colonies provide unique habitats for other organisms (metazoans, bacteria, and viruses) and serve as hot-spots for microbial mediated nutrient transformations within the oligotrophic oceans. While this phenomenon is a well-known trait of Trichodesmium the mechanisms for the formation of these structures are not understood.
In my research, I am interested in determining what causes the single filaments to create colonies; to reveal the cues and mechanisms involved in creating colonies from single trichomes. My work will combine live-imaging microscopy as well as molecular and physiological techniques.
Biofilm prevention in the desalination industry
Limitations of global freshwater supplies have stimulated the application of desalination technology with desalinized water coming online worldwide at a rate of 40 to 50 million m3 d−1. Currently, about 50% of global desalination is based on filtration through reverse osmosis (RO) membranes requiring effective pretreatment procedures upstream to reduce fouling, maintain performance and extend membrane lifetime and to ensure the manufacturers requirements for membrane recovery yield. Transparent exopolymer particles (TEPs) are sticky, organic microgels, ranging in size from ∼0.4 to >200 μm, present in large numbers in all aquatic environments. Recently, TEPs have been implicated as an important factor in the development of aquatic biofilm and are part of the extracellular polymeric substances (EPSs) that form the matrix of microbial biofilms.
In our research we examined the direct involvement of these microgel particles in biofilm development. We showed that protobiofilm and TEPs in the feedwater contributed to fast development of biofilm and not EPSs generated by adhering, single bacteria, or bacterial aggregates. In addition, experiments comparing the initial stages of biofilm formation in filtered or in untreated seawater clearly illustrate the importance of protobiofilm and TEPs in accelerating aquatic biofilm formation.
Schematic illustration showing the involvement of organic polymers and colloids, TEP and protobiofilm in the initial stages of aquatic biofilm formation. Immediately upon exposure to seawater, organic polymers and colloids (a) and microgels such as uncolonized TEP (b) and protobiofilm (c) begin to attach to pristine surfaces. Single cells of planktonic bacteria also attach reversibly (d) or irreversibly (e) to conditioned surfaces. With time (minutes to hours) a contiguous coverage of mature biofilm (f) develops. From Bar-Zeev et al. 2013.PNAS
Desalination impacts on microbial coastal populations
The increasing importance and expansion of seawater desalination technologies and large scale coastal plants – enhances both the “visibility” and essentiality of ensuring environmental sustainability of the impacted coastlines. Our study (2015-2019) added important knowledge to the scant information that has been published either locally or globally to examine the impacts of desalination discharges on the coastal microbial communities comprising the foundation of the aquatic food webs. Our overarching goal in this project was to characterize and predict the responses of microbial and phytoplankton communities to their exposure to both enhanced salinities and chemical discharges resulting from desalination plants.
The comprehensive results of this study including the in-situ sampling, experimental manipulations, hydrodynamic simulations of plume and intake effects, and modeling brine (and temperature impacts) on the aquatic food-web all demonstrate the following. Impacts are influenced by both seasonality and site-specificity with salinity and temperature both driving biological changes. Therefore, site-specific monitoring and assessment of changes of the microbial populations is essential. Moreover, Coastal environments, exposed to long term discharge of brine, may exhibit cumulative chronic effects and affect the ecosystems more dramatically. The assessment of ecological impacts, from the rapidly expanding desalination industry, on coastal marine environments and their biota should be included as a routine monitoring tool and not be based solely on the results of short term studies such as this one.
Past students and Post doctoral Fellows
Nurit Amitai, MsC 2018, Effects of Antiscalants from Seawater Desalinatio Discharges on Coastal Bacterial and Phytoplanktonic Communities of the Eastern Mediterranean Sea
Liel Magnezi, Msc 2018, Trichodesmium bloom formation
Dan Miller, PhD 2018, Assessing the physiological and compositional response of coastal microbial populations to increased pCO2 and to eutrophication
Natasha Belkin, PhD 2016, Impacts of seawater desalination discharges on coastal bacterial and phytoplanktonic communities
Reut Sorek Abramovich, PhD. Post-doc fellow, 2015 Toxins in Trichodesmium
Adi Levi, PhD 2015, Applying innovative nano-technology approaches to reduce biofilm development on membrane and surfaces in the desalination industry
Eyal Rahav, PhD 2013, Controls on dinitrogen fixation in the eastern Mediterranean
Edo Bar Zeev, PhD 2012, TEP and biofilm formation; MSc 2007, Nitrogen fixation in aquatic symbiotic associations
Itamar Avishai, MSc 2012, Programmed cell death in Trichodesmium
Sara Ohaion, MSc 2012, Molecular diagnostics of controls on N2 fixation
Ben Brinberg, MSc 2013, Microbial ecology of subterranean estuaries of Mediterranean coastline
Tali Yogev, PhD 2009, Nitrogen fixation in the eastern Mediterranean
Orly Levitan, PhD 2010, Impacts of CO2 on aquatic dinitrogen fixation; MSc 2005, Influence of CO2 on aquatic nitrogen fixation
Eric Ben David, Post-doc fellow 2010, Programmed cell death in Trichodesmium
Tamar Bsor-Rachamim, PhD 2010, Nutrient recycling by zooplankton in Lake Kinneret
Max Rubin, MSc 2009, Fe uptake in Trichodesmium
Sammy Frenk, MSc 2008, Ammonium supply for optimal growth of juvenile and mature thalli of Porphyra rosengurtii (Rhodophyta)
Gad Rosenberg, MSc 2007, Programmed cell death in Trichodesmium
Dovi Kelman, Post-doc fellow 2007, Natural products from Trichodesmium
Chen Sherman, MSc 2006, Effect of varying pH on Trichodesmium