Abstract
Diatoms are highly abundant unicellular algae that often dominate pelagic as well as benthic primary production in the oceans and inland waters. Being strictly dependent on silica to build their biomineralized cell walls, marine diatoms precipitate 240 × 1012 mol Si per year, which makes them the major sink in the global Si cycle. Dissolved silicic acid (dSi) availability frequently limits diatom productivity and influences species composition of communities. We show that benthic diatoms selectively perceive and behaviourally react to gradients of dSi. Cell speed increases under dSi-limited conditions in a chemokinetic response and, if gradients of this resource are present, increased directionality of cell movement promotes chemotaxis. The ability to exploit local and short-lived dSi hotspots using a specific search behaviour likely contributes to micro-scale patch dynamics in biofilm communities. On a global scale this behaviour might affect sediment–water dSi fluxes and biogeochemical cycling.
Highlights
Diatoms are highly abundant unicellular algae that often dominate pelagic as well as benthic primary production in the oceans and inland waters
When stationary-phase S. robusta cultures were transferred to artificial sea water without added Dissolved silicic acid (dSi) and were further starved for 3 days, cell movement was more than twice as fast than that of cells transferred to dSi-rich control medium (Fig. 1c)
Our results clearly indicate the specific modulation of foraging behaviour of benthic diatoms in response to silicate
Summary
Diatoms are highly abundant unicellular algae that often dominate pelagic as well as benthic primary production in the oceans and inland waters. While the pelagic zone is often dSi-limited below 1 mM, the benthic zone typically shows strong and steep gradients of this resource with higher dSi concentrations (around 150 mM) in the sediment due to the continuous dissolution of deposited minerals[6] Because of their high productivity and biomineralization activity, benthic diatom biofilms can influence sediment properties[7] and alter dSi fluxes within the sediment–water interface, regulating dSi concentrations in the oceans[8]. When a pseudopod or stalk is adhering to the substratum resulting torque supports the whole-cell rotation[15] In this contribution, we describe three sets of experiments where we first look at the general influence of dSi concentration on diatom motility, we observe and analyse diatom behaviour in a dSi gradient and last, we test the specificity of the response by comparing the reaction towards dSi and dGe gradients. The fact that structurally closely related dissolved germanium dioxide (Ge(OH)[4], dGe) sources are not eliciting attraction suggests a specific receptor-mediated response
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