Interactions between phytoplankton and bacteria in a productive coastal system

Resumo

In marine environments, the phytoplankton has coexisted with bacteria for millions of years. The interactions between phytoplankton and bacteria are ubiquitous and complex, they encompassing everything from mutualism to competition. Many of these interactions are an exchange of metabolites, which could benefit or harm the involved species. Recent studies suggest that interactions between phytoplankton and bacteria may be the key to keep the productivity in marine systems. It establishes like the main objective of the thesis: to detect relevant interactions between pairs of phytoplankton-bacteria species in coastal water in front of the Ría de Vigo, and to identify the involved metabolites. In a first phase, it will analyse a database of the RNAr-16S and RNAr-18S partial sequences from 42 shelf water samples, which were taking in front of the Ría de Vigo between 2014 and 2015. The database analysis will allow detection of pairs of phytoplankton-bacteria species that co-occur in these coastal waters. In a second phase, it will use a co-culture systems to confirm experimentally if the pairs of co-ocurring species interact with each other. The purpose of the co-cultures is to decide if the phytoplankton growth in a basic culture medium is stimulated or inhibited in the presence of pertinent bacterial specie. In the current thesis, metabolites that may be part of the interactions will also be determined by transcription analysis of the co-culture samples. The research of the seaweed-bacteria interactions has a high number of applications, both to environmental and biotechnological levels. Comprehending the interaction patterns between phytoplankton and bacteria will allow us to better understand and manage the marine resources. This gets a great amount of attention in Galicia, because of the economic repercussions of the massive proliferation of toxic phytoplankton in the aquaculture. An important section inside this investigation project is classified in our findings in a context of global change to understand the response of microplankto to problems, such as the increase of CO2 in the atmosphere or the boost of ocean intakes of anthropogenic nutrients.