Ion-driven communication and acclimation strategies in microalgae

Similar to all living organisms since their appearance on Earth, microalgae have continuously been exposed to natural selection and consequently evolved by adapting to different or changing ecological niches and occupying ecosystems worldwide, with concomitant genetic mutations. This has to be distinguished from acclimation, a response to environmental stressors which can occur over several generations without genetic changes, and for which phenotypic plasticity can be critical. Pertaining to both mechanisms, microalgae can sense, cooperate and propagate a timely warning message upon changes in the environment. This is key to maintain communities thriving and sustain primary production and mineralization in most ecosystems, but also for sustainability in large scale production of microalgae such as for biofuels production. Nevertheless, the nature of ubiquitous cell–cell interactions and communications, mostly prompted by stress-induced alterations, remains poorly understood, especially due to the lack of technologies suited to decipher cohort signalling and communication. Here, we have critically reviewed microalgae literature, unravelling important cues in microalgae populations that co-ordinate responses to changes in light, temperature, reproduction, grazers and osmotic stress, most likely through a mass diffusion process over a “handover distance”. We concluded that bioelectricity mediated through paracrine signalling, mostly involving Ca²⁺, plays a key role in microalgae cell sensing and communication, being the mediator for timely perception and concomitant collective stress acclimation. This critical analysis and the hypothesis proposed pave the way for quantitative electrogenic assessments of Ca²⁺ signalling and also of the acclimation potential and exquisite evolutionary perseverance of numerous microalgal lineages.