『Abstract
　Dissolution of diatom biogenic silica (bSiO2) in estuaries and its control by water salinity and bacteria were investigated using the river euryhalite species Cyclotella meneghiniana as a model. Laboratory-controlled bioassays conducted at different salinities with an estuarine bacteria inoculum showed a faster dissolution of diatom bSiO2 at the lowest salinity where bacteria were the most abundant. However in another experiment, salinity increase clearly enhanced the dissolution of cleaned frustules (organic matter free). The presence of active bacteria might therefore predominate on the effect of salinity for freshly lysed diatoms whereas salinity might rather control dissolution of organic-matter-free frustule remains. Incubation of cultivated diatoms at different protease concentrations revealed that high proteolytic activities had little effect on bSiO2 dissolution at a 1-month scale in spite of an efficient removal of organic matter from the frustules. Altogether it is hypothesized that bacterial colonization increase bSiO2 dissolution by creating a microenvironment at the diatom surface with high ectoproteolytic activity but also via the release of metabolic byproducts since the presence of organic matter seems generally to facilitate diatom bSiO2 dissolution.

Keywords: Bacteria; Biogenic silica; Diatoms; Dissolution; Estuaries; Salinity』

Introduction
Materials and methods
　Experimental setup
　Bioassays 1: diatom bSiO2 dissolution at different salinities with estuarine bacteria
　Bioassays 2: dissolution of cleaned diatom frustules at different salinities
　Bioassays 3: dissolution of fresh bSiO2 with different protease concentrations
　Bioassays 4: comparative dissolution of fresh and cleaned diatom frustules
　Analytical measurements
　　DSi and bSiO2
　　Bacterial biomass
　　Proteolytic activity
　　Particulate organic matter
　Dissolution rate calculations
Results
　Diatom bSiO2 dissolution under estuarine conditions
　Effect of salinity on the dissolution of cleaned diatom frustules
　Effect of proteases on the dissolution of fresh diatom bSiO2
　Different dissolution of fresh diatom frustules and cleaned frustules
Discussion
　bSiO2 dissolution model
　Comparison with other studies
　The effect of salinity
　The role of bacteria
　The control of salinity and bacteria on bSiO2 dissolution in estuaries
Acknowledgements
References