Abstract
Microorganisms encounter a diversity of chemical stimuli that trigger individual responses and influence population dynamics. However, microbial behavior under the influence of different incentives and microbial decision-making is poorly understood. Benthic marine diatoms that react to sexual attractants as well as to nutrient gradients face such multiple constraints. Here, we document and model behavioral complexity and context-sensitive responses of these motile unicellular algae to sex pheromones and the nutrient silicate. Throughout the life cycle of the model diatom Seminavis robusta nutrient-starved cells localize sources of silicate by combined chemokinetic and chemotactic motility. However, with an increasing need for sex to restore the initial cell size, a change in behavior favoring the attraction-pheromone-guided search for a mating partner takes place. When sex becomes inevitable to prevent cell death, safeguard mechanisms are abandoned, and cells prioritize the search for mating partners. Such selection processes help to explain biofilm organization and to understand species interactions in complex communities.
Highlights
Diatoms are a species-rich group of silicifying microalgae responsible for about 20% of global carbon fixation [1]
We chose a final concentration of 4 nmol diproline per mg beads, which is within the bioactive concentration range of the pheromone [14] and was previously used for movement pattern analysis [15]. dissolved silicate (dSi) beads were prepared according to Bondoc et al [19], wherein 1.4 nmol dSi was loaded per bead
We investigated the behavioral responses towards pheromones and dSi
Summary
Diatoms are a species-rich group of silicifying microalgae responsible for about 20% of global carbon fixation [1]. Motile pennate diatoms often dominate the soft sediment substrata of aquatic habitats, forming biofilms that can contribute substantially to ecosystem productivity and provide important ecosystem services such as sediment stabilization [3]. These phototrophic biofilms typically represent a dynamic, spatially heterogeneous environment. Directional responses in many raphid pennate diatoms are enabled by a characteristic forward and backward movement that is mediated by the excretion of adhesive extracellular polymeric substances [7]. Cells can undergo turning movements using pseudopod-like structures that temporarily attach to the substrate [8]
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