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Abstract

Diatoms frequently dominate marine and freshwater biofilms as major primary producers.
Nutrient resources in these biofilms are patchily distributed and fluctuate
dynamically over time. We recently reported that this spatially and temporally structured
environment can be exploited by motile diatoms that use chemoattraction to
dissolved silicate (dSi) under Si starvation. Here, we show that the behavioral response
of diatoms is more complex and selective as cells are also responding to gradients
of dissolved phosphate (dP) when starved in this nutrient. In contrast, neither
nitrate nor ammonium (dN) triggers an attractive response under nitrogen limitation.
Video monitoring and movement pattern analysis of the model diatom Seminavis robusta
revealed that dP attraction is mediated by a combined chemokinetic and
chemotactic
response. After locating nutrient hotspots, the microalgae slow down
and recover from the limitation. The fastest recovery in terms of growth was observed
after dSi limitation. In agreement with the lack of directional response, recovery
from dN limitation was slowest, indicating that no short-term
benefit would be
drawn by the algae from the location of transient hotspots of this resource. Our results
highlight the ability of diatoms to adapt to nutrient limitation by active foraging
and might explain their success in patchy benthic environments.