The Mediterranean Sea has nurtured and sustained its surrounding populations for thousands of years. Yet, food and energy requirements of increasing populations have contributed to a greater human (anthropogenic) footprint on the Mediterranean. The recent discoveries of large natural gas reservoirs (1.8% of world reserves) and possibly oil in the Levant Basin of the eastern Mediterranean Sea (EMS) have stirred excitement over the new prospects yet raise stakeholders concerns about the environmental risks involved in the large-scale exploitation of these offshore resources.
Marine hydrocarbon pollution affects pelagic, benthic, and coastal populations as well as commercially grown organisms. Primary producers and bacterioplankton form the basis of marine food webs and are essential for biogeochemical cycling of nutrients such as carbon (C), nitrogen (N), and phosphorus (P). Many studies have examined the response of individual species of algae or bacteria with several studies examining the integrated responses of natural communities of marine pelagic and coastal microbial populations including primary producers to either acute or chronic hydrocarbon pollution. Yet, the large variability of both pollutants and the natural environments/ecosystems make community responses hard to predict requiring experimentation according to specific locality and conditions.
This project will be funded starting October 2014, candidates for PhD are encouraged to apply.
Featured top Image. Reverse Osmosis membranes in a full-scale desalination membrane. Insert shows biofouling on membranes.
Fig 1. 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
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.
Photosynthesis and fixation of atmospheric dinitrogen which are two fundamental processes that are performed by organisms at the basis of aquatic food webs – the phytoplankton and bacterioplankton. Dinitrogen fixation is a biological transformation carried out only by a subgroup of prokaryotic organisms (diazotrophs) that can utilize atmospheric nitrogen (N2), unavailable for most organisms, and convert it into a form of nitrogen that is used for growth. This process is extremely important in many nitrogen-poor surface waters of the oceans, and injects a new source of bioavailable nitrogen to areas where nitrogen limits growth and primary production by the ocean’s tiny plants – the phytoplankton.
In our research we explore how diazotrophs influence bio-geochemical cycling of carbon and nitrogen in the face of climatic changes. These changes include global warming and ocean acidification due to increased dissolution of atmospheric CO2 in the oceans.
We have specifically examined changes in natural populations of diazotrophs from the Red- and the Mediterranean Seas under the combined effects of elevated CO2 and higher temperatures as well as variations in essential nutrients such as phosphate and iron.
Collaboration with Dr. Yeala Shaked (IUI- Hebrew University) on iron uptake of Red Sea populations of Trichodesmium (a globally important N2 fixer in the tropical and subtropical oceans with blooms extending over thousands of kilometers) has illustrated that the colonies actively take up and shuttle Fe along the filaments to the center of the colony where it is dissolved and assimilated into the cells (Photo 1). We have also demonstrated that the future projections of high CO2 in the oceans can enhance nitrogen fixation and growth of this marine cyanobacterium and indicate that Trichodesmium will thrive in the future warmer and more acidified oceans (Photo 2).
Further research on other diazotrophs in the Gulf of Eilat shows that a large diversity including bacterioplankton. These are not restricted like the phytoplankton to the upper sunlit areas of the surface oceans, and can fix nitrogen in deep dark layers. We measure N2 fixation rates from oceanic zones that have traditionally been ignored as sources of biological N2 fixation; the dark, fully oxygenated, nitrate (NO3–)-rich, waters of the oligotrophic Gulf of Aqaba and the eastern Mediterranean. Our results suggest that while N2 fixation may be limited in the surface waters of the oligotrophic Mediterranean and Red Seas, N2 fixation from the deeper and dark ocean layers may contribute significantly to new N inputs, yet these inputs are currently not included in regional or global N budgets.
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
Biological fixation of atmospheric dinitrogen can contribute significant amounts of biologically available dinitrogen to the nitrogen-limited surface waters of the oceans and induce subsequent biological production