Symbiotic microorganisms play critical ecophysiological roles that facilitate the maintenance of coral health. Currently, information on the gene and protein pathways contributing to bleaching responses is lacking, including the role of autoinducers. Although the autoinducer AI-1 is well understood, information on AI-2 is insufficient. Here, we observed a 3.7-4.0 times higher abundance of the AI-2 synthesis gene luxS in bleached individuals relative to their healthy counterparts among reef-building coral samples from the natural environment. Laboratory tests further revealed that AI-2 contributed significantly to an increase in coral bleaching, altered the ratio of potential probiotic and pathogenic bacteria, and suppressed the antiviral activity of specific pathogenic bacteria while enhancing their functional potential, such as energy metabolism, chemotaxis, biofilm formation and virulence release. Structural equation modeling indicated that AI-2 influences the microbial composition, network structure, and pathogenic features, which collectively contribute to the coral bleaching status. Collectively, our results offer novel potential strategies for coral conservation based on a signal manipulation approach.
Most signaling molecules are involved in inter-or intra-species communication, and signaling involving cross-kingdom cell-to-cell communication is limited. Howerver, algae and bacteria exchange nutrients and information in a range of interactions in marine environments. Multiple signaling molecules exist between algae and bacteria, including quorum-sensing molecules, nitric oxide, and volatile organic compounds. Recently, indole-3-acetic acid (IAA), an auxin hormone that is a well-studied signaling molecule in terrestrial ecosystems, was found to act as a cue in cross-kingdom communication between algae and bacteria in aquatic environments. To increase understanding of the roles of IAA in the phycosphere, the latest evidence regarding the ecological functions of IAA in cross-kingdom communication between algae and bacteria has been compiled in this review. The pathways of IAA biosynthesis, effects of IAA on algal growth & reproduction, and potential mechanisms at phenotypic and molecular levels are summarized. It is proposed that IAA is an important molecule regulating algal–bacterial interactions and acts as an invisible driving force in the formation of algal blooms.
Abstract Understanding how organisms adapt to unpredictable future environments is a fundamental goal in biology, which becomes even more urgent in an era of rapid climate change. One evolutionary adaptation to randomly fluctuating environments is bet hedging, a strategy that successfully facilitates reproduction and population persistence and has been widely reported from microbes to humans. Empirical evidence for its presence in microalga, one of Earth’s most important primary producers and carbon sinks, is lacking. Here, we report a bet-hedging strategy in the unicellular microalga Haematococcus pluvialis. In a series of experiments, we show that an isogenic H. pluvialis population reversibly diversifies into hetero-phenotypic mobile and non-mobile subunits, independent of environmental conditions. Mobile cells grow faster but are more susceptible to external stressors, while non-mobile cells hardly grow but are more stress-resistant. This is attributed to dramatic shifts from growth-promoting activities (cell division, photosynthesis) to resilience-promoting cellular metabolic processes, including cell enlargement and aggregation, and accumulation of antioxidant and energy-storaging compounds. Our results provide experimental evidence for bet hedging in microalga, which has implications for their potential to adapt to current and predicted future conditions, and thus for the conservation of ecosystem functions.
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