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Special Session 3: Size matters or not, particles export in marine environments |
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How to export pico-phytoplankton to the deep
Tuesday 10th @ 1210-1230
Room 4
Tiantian Tang* , State Key Laboratory of Marine Environmental Science (Xiamen University)
Presenter Email: tiantian.tang@xmu.edu.cn
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| Accumulating evidence suggests that the cellular remains of pico-phytoplankton can be transported out of the Euphotic zone and potentially contribute to a major portion of exported particles in the deep ocean. However, it remains a mystery how the pico-size cell debris can be preserved against the preferential decomposition of small particles during their journey to the deep. Here we provide evidence that two mechanisms, mineral association and protection by membrane proteins respectively, may be involved in the preservation of a broadly distributed pico-phytoplankton species, cyanobacterium Synechococcus sp.
Silicon was found to be enriched in a previously unexplored group of marine particles (called micro-blebs) from the deep-water column, which was suggested to originate from the silicate associated organic matter (Si-OM) produced during the decomposition of cyanobacteria. Our work on silicate budget in the decomposing cyanobacteria finds the accumulation of Si-OM from the cell debris grown and decomposed in the oligotrophic surface water from the South China Sea with limited Si supplied. This finding suggests the universal existence of Si-OM in various marine environments and proves the origins of Si-OM in the deep water.
Meanwhile, with special attention to its possible geochemical importance, a membrane protein, surface layer protein (S-layer) from synechococcus was investigated. This heavily glycosylated protein covers the outermost cell surface in a regularly ordered planar crystalline structure. Based on bulk chemical and molecular analysis as well as electron microscopy, stripped cells with S-layer structure physically removed degraded more rapidly and became more enriched in D-amino acids as well as other degradation indicators. This result suggests that S-layer structure functions as a defensive barrier on the cell membrane to prevent cell lysis and slow degradation of cyanobacterial cellular materials.
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