WP2 : Effect of microbial diversity on ecosystem functioning

Using microcosm experiments we will assess and quantify (1) the effect of diatom taxonomic and functional diversity on photo- and mixotrophic C uptake by diatoms, and (2) the effect of diatom and bacterial taxonomic and functional diversity on the C flow to bacteria. It has been shown that a wide range of bacteria can incorporate EPS-C (e.g. 48). However, unpublished data from PAE-UG (Stock, unpubl. data) have shown that some bacterial taxa preferentially occur in association with benthic diatoms (e.g. Sulfitobacter and Loktanella). We will test whether this association is mediated by enhanced EPS-C assimilation in these taxa. C flows will be identified and quantified using 13C labelling experiments, either using labelled inorganic or organic C sources, in combination with RNA-SIP and nanoSIMS (Nanoscale Secondary Ion Mass Spectrometry). This method allows quantifying isotopes at superior spatial resolution (50-100 nm), making it ideally suitable for use in environmental microbiology (51). The use of nanoSIMS in tidal flat sediments is new and will require a significant investment in protocol development (e.g. by trying semithin sections or block faces instead of TEM because of the presence of sediment particles). The diatom strains will be obtained from the Ghent (http://bccm.belspo.be/about- us/bccm-dcg) and Nantes University (http://ncc.univ-nantes.fr/) cuIture collections who hold 100s of benthic diatom strains belonging to different species and functional groups. In addition, about 50 bacterial strains obtained from tidal flat biofilms and diatom cultures are available at UG-PAE.

Task 2.1 – Effect of taxonomic and functional diatom diversity on photrophic and mixotrophic C flux in axenic experimental biofilms
Task 2.2. – Effect of bacterial and diatom diversity on bacterial C uptake in experimental diatom-bacteria biofilms
Task 2.3 – Effect of taxonomic and functional diatom diversity on EPS production and functionality (sediment stability)