Research

Dust as a Source of Iron & Phosphorus to Trichodesmium 

Desert dust is an important source of the nutrients iron (Fe), phosphorus (P), and nitrogen (N) to remote ocean regions, supporting phytoplankton growth and carbon cycling. Desertification induced by global climate change is expected to increase dust fluxes to the ocean. Elucidating the ability of phytoplankton to utilize nutrients from dust, an integrative line of research we have been advancing over the last 12 years, will assist in predicting the function of the ocean as a life-supporting system in the global change era.   

Studying natural Trichodesmium colonies from the Gulf of Aqaba, we discovered unique adaptive mechanisms for capturing and storing dust particles within the colony core, enabling efficient utilization of Fe (and P) from dust. We documented a variety of biochemical pathways and physical mechanisms that assist Trichodesmium to obtain Fe from mineral sources. We showed that dust packaging in the colony core is beneficial for uptake, since cell-particle proximity minimize Fe loss by diffusion, and that natural colonies enhance dissolution rates of dust-Fe and Fe-minerals. Lately we found that Trichodesmium and its associated bacteria act together to increase availability of dust-bound iron, where bacteria secrete Fe-binding molecules that promote dust dissolution and Trichodesmium provides dust and optimal physical settings for dissolution and uptake. In addition, we revealed that Trichodesmium can sense Fe and selectively choose Fe-rich dust particles, thus optimizing Fe supply.

Over the last years we expanded our research to the nutrient P and added new disciplines and techniques such as molecular biology (identify microbial interactions and biochemical response to dust), organic chemistry (siderophore characterization), high resolution imaging (Synchrotron, MALDI, NanoSIMS) and micro-electrodes (identify chemical gradients). Trichodesmium is predicted to flourish in the warmer, acidified and “dusty” future ocean. The mechanistic understanding gained by our research on its ability to utilize dust as a nutrient source will enhance our ability to predict the ocean’s operation modes in face of global change, and hence its impact on the atmosphere and climate.

 Dynamics of Reactive Oxygen Species in the Coral Reef

In corals and other reef inhabiting invertebrates reactive oxygen species (ROS) and antioxidants were shown to be involved in various metabolic pathways such as communication and reproduction, stress and immune responses and in the onset of infectious diseases and bleaching. Nonetheless, direct measurements of ROS in corals are conspicuously rare, partly due to inherent problems with ROS quantification in cellular systems. 

Applying fast and sensitive chemiluminscence based technique we investigate the O2- and H2O2 dynamics in the immediate surroundings of the coral; its external milieu. Our findings of substantial extracellular O2- production by corals and their symbionts as well as the release of antioxidants to the surroundings water may shed light on the chemical interactions between the symbiont and its host and between the coral and its environment. We are planning to map and quantify ROS (O2- and H2O2) production and detoxification activities in a natural coral reef under various irradiation doses, temperatures, sea levels and currents. Then, scaling down from the ecosystem to the level of the organism, we plan to conduct controlled experiments with corals, symbiotic algae and mucus-associated bacteria to examine the effects of environmental stressors on both the production and detoxification of ROS by the different members of the coral holobiont.