Microbial stimulation of the aggregation process between submicron-sized particles and suspended particles in coastal waters

摘要

Transfer rates of submicron-sized particles (SMP) to micro-suspended particles (5 to 20 mum in diameter) in coastal waters around Japan were measured using fluorescent beads (0.5 mum in diameter) and flow cytometry, with and without metabolic inhibitors (thiuram. or NaN3) This flow cytometric technique has the advantage that it allows the number of beads stuck to suspended particles to be counted without any pre-treatment, such as filtration, that can introduce artifacts. The transfer rates to particles in the 5-20 mum fraction without inhibitors were on average 4.3 to 5.8 times higher than with added NaN3. On the other hand, ingestion rates of fluorescent beads by protozoa in the 5-20 mum fraction were less than 10% of the transfer rates to particles in the 5-20 mum fraction. These results indicate that biological activities were more efficient than physical mechanisms for the transfer process of SMP into the 5-20 mum fraction separately from the grazing process. Also, the inhibitory effect of thiuram on the transfer rates suggests an involvement of eukaryotic cells in this stimulation. The intensity of this stimulation was positively correlated with the density of attached nanoflagellates per particle (Da) (R = 0.630, n = 22), bacterial abundance (R = 0.489, n = 22), concentration of chlorophyll a (R = 0.518, n = 18) and water temperature (R = 0.569, n = 22). These results indicate that biological processes are key mechanisms for the coagulation process of submicro- and micro-scale particles in coastal environments.