Johanna Berlinghof

In my PhD project, I study the seagrass holobiont and how it is affected by anthropogenic impacts. I already had the chance to analyze data from previous experiments, examining the effects of ocean acidification on biogeochemical cycling in the seagrass Posidonia oceanica and its associated epiphytes. For the second part of my PhD, I aim to investigate the relationship between P. oceanica, the sponge Chondrilla nucula that can live in close association with the plant, as well as their respective microbiomes. Therefore, I wanted to do incubation experiments, where I added different isotopic tracers of nitrogen. Since these experiments are conducted in closed incubation chambers, and we know the initial and final amounts of different molecular compounds, we can draw conclusions about the biogeochemical processes that happened in between.

The first week of my research stay was dedicated to getting to know the institute, my colleagues, and to start with the preparations for the fieldwork. In the following week, we went out to explore our fieldwork site and the seagrass meadows. The day after, we conducted the first of three incubation experiments to assess nitrogen fixation by adding ¹⁵N₂ gas as isotope tracer. We collected P. oceanica and C. nucula growing alone and in association and incubated them in the light and the dark for six hours. After the incubation, we took samples from each incubation chamber to analyze organic and inorganic nutrients, dissolved gases, and isotopic composition of the tissue. A similar approach was used for the following two incubation experiments in the third week. Here, we added ¹⁵NH₄⁺ to assess nitrification and ¹⁵NO₃^- to assess denitrification in the seagrass-sponge-holobiont. The time between the experiments I used for preparations and processing of the samples we took.

In my last week at the SZN, I participated in the bioinformatics course given by Dr. Maria Luisa Chiusano, Prof. of Molecular Biology at the University of Naples and SZN. It was a good overview of different bioinformatics approaches. Topics covered were transcriptomics, metabarcoding and metagenomics, and data sharing. We also had practical parts where we learned sequence alignment and functional annotation of genes with different software tools. This was especially interesting since there are multiple ways to conduct each step in a metagenomic pipeline. On the weekends, I explored the city of Naples (they have the best pizza and ice cream!) and took the chance to visit the ruins of Pompeii (highly recommended!). After four weeks in Naples, I headed back to Bremen with tons of new impressions, samples to be processed, and data to be analyzed in the upcoming time.