Characterizing mycoplankton and the mycobenthos in the Benguela upwelling system
Oceanography
Final Report Abstract
Mycoplankton and mycobenthos are heterotrophic eukaryotic microbes, including Fungi and fungal-analogs, that live in seawater and sediments, respectively. They are hypothesized to play an important role in the biological pump through their degradation of dead organic matter. It has been hypothesized that they are also important heterotrophic organisms in marine food webs. This project provides novel data that sheds light onto the mechanisms of fungal carbon cycling in the ocean under different environmental conditions. We performed the first comparison of fungal gene expression in water samples compared to the sediment samples, which show that Fungi gene expression increases at the seafloor, at the sediment water interface. The gene expression data also show that the Fungi detected have significantly different patterns of gene expression in waters of varying oxygen concentrations, which were significantly different in terms of gene expression compared to fungal expressed genes in the underlying sediments. In the nitrate sulfide transition zone in the sediments, there is an increased fungal abundance that coincides with higher abundances of 16S rRNA gene copies from bacteria and archaea. A 13C DNA-SIP experiment demonstrated that the Fungi are growing in this redox interface by feeding on the necromass of autotrophic prokaryotes that are performing “dark” carbon fixation. Namely, the DNA of Fungi in the Namibian sediments was labeled in a 13C-SIP incubation with 13C-labeled CO2 after a 10-day incubation in the dark at 10 °C. The ITS sequencing showed that most of the Fungi in the sediments are single celled yeasts or microfungi, indicating that likely to be responsible for the carbon turnover observed in the DNA-SIP experiment. The gene expression data that have been produced from both the water column samples and the sediments will be used to reconstruct the fungal metabolism and anaerobic energy metabolism. This will be integrated with the DNA-SIP experiment to identify the mechanisms of anaerobic energy metabolism in actively carbon cycling Fungi in marine sediments. These data will establish for the first time the quantitative importance, and biological mechanisms, of marine Fungi in marine sedimentary carbon cycling. This will expand knowledge as to the role of Fungi in the marine carbon cycle, both in the benthos and also in the water column.
Publications
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(2020) Metabolic activity analyses demonstrate that Lokiarchaeon exhibits homoacetogenesis in sulfidic marine sediments. Nature Microbiology 5: 248–255
Orsi W, Vuillemin A, Rodriguez P, Coskun O, Gomez G, Mohrholz V, Lavik G, Ferdelman T
