During these two years of the project, I have been studying and characterizing vesicles of the most abundant phototrophic cyanobacteria Synechococcus to gain insight into the ecology and function of these membrane vesicles.
It is known that starvation can induce extensive stress response pathways in bacterial cells, however we have demonstrated in this project that outer membrane vesicles production increase during phosphorus starvation condition, even when the culture looks stable. However, when the nutrient starvation is nitrogen, vesicles tend to decrease with a low protein concentration inside, what it might make sense since nitrogen is considered the primary nutrient limiting in the development of cyanobacteria.
Moreover, in this project we have demonstrated that light shock stimulates vesiculation more than 5 times and with more than double of protein. We found that under light shock vesicles released proteins involved in stress tolerance as superoxide dismutase, chaperones, pigments but also ferredoxins and GS-GOGAT proteins which are involved in the electrons transfer from the photosystem. Moreover, in control samples we identified photosystem I and II proteins which were not identified under the treatment what would demonstrate damage to PSII and PSI than the wild type. The protein CtpA, encoding the carboxyl-terminal processing protease involved in the maturation of the PSII core subunit D1 also increased during the treatment.
Due to the damaging nature of Reactive Oxygen Species (ROS), very efficient scavenging (or antioxidant) mechanisms exist in chloroplasts to prevent oxidative damage: 1O2 can be quenched by pigments and the superoxide dismutase. The excess of electrons in the photosynthetic electron chain could explain the increase of proteins involved in the transfers of electrons as ferrodoxins and GS-GOGAT. Light stress is deleterious for the photosynthesis, and that the full recovery of damaged PSII from light shock might involve the neo-synthesis of a large number of PSII subunits and not just the reassembly of pre-existing subunits after D1 replacement.
Another stress-specific response related to photosynthesis is the significant induction of proteins coding for all ATPase subunits in response to high light stress. This suggests that, although cells seemingly actively respond to the increase in irradiance by reducing the number of photosystems and their light harvesting capacity (as demonstrated by the downregulation of most genes involved in biosynthesis of PSI as well as PSII subunits), they are able to use the extra photons provided by the increase in light intensity to enhance energy production.
The reason why we found all these proteins inside vesicle might be related with the abundance of the proteins existing in the membrane, before vesiculation. Moreover, all these results accumulate evidence that membrane vesicles endow bacteria with an extraordinary capacity to survive in stressful conditions and are considered to be a potent bacterial innate immune element.
During the project I promoted a new collaboration between Prof. Steve Biller and Penny Chisholm with the Prof. García-Fernández, leaders of two groups that have not collaborated before. For that, I spent a short stay in Penny´s lab at the Massachusetts Institute of Technology (Cambridge, USA) to exchange information in this subject. During this stay, Prof. Biller taught me to isolate, concentrate and characterize marine vesicles. Moreover, we started a few experiments working with Synechococcus WH7803 and WH8102 under different kind of stress. These experiments helped me to set up protocols in my lab and bring us the axenic cultures I needed to start the project at the University of Córdoba. Steve also taught me to quantify vesicles with the nanoparticles tracking analysis (Nanosight).
Achieving a greater understanding of the ocean and, particularly, of the organisms driving key biogeochemical process such as primary production, is crucial towards developing efficient environmental management policies by the public administration. For that reason, in this project I created a dissemination blog called “Capitana Vesy” (
http://www.uco.es/investigacion/proyectos/capitanavesy/index.php/es/(si apre in una nuova finestra)) in English and Spanish languages, thanks the educational platform “Scientific Culture and Innovation Unit” at the University of Córdoba, who help me with the creation of a public image for a exhibition ship and the creation a blog where I share the multidisciplinary talks, conferences in schools and presentations to the general public.
