Periodic Reporting for period 1 - PHYCOSPHERES (Structure and functions of terrestrial phycospheres)
Reporting period: 2023-03-01 to 2025-08-31
Photosynthetic organisms such as terrestrial algae are pivotal players in global ecological processes, significantly contributing to nutrient cycling, soil formation, and ecosystem stability. Despite extensive studies of green algae from aquatic environments, terrestrial microalgae and their interactions with soil microorganisms remain largely unexplored, despite of their abundance and prevalence. Terrestrial algae exist primarily at soil surfaces, where there is an abundance of light and CO2. In this habitat, they encounter complex communities of bacteria, fungi, and other microbes. These microbial assemblaes, known collectively as the "phycosphere microbiota," influence algal growth, survival, and ecological function.
This research project aims to deepen our understanding of the ecological and molecular mechanisms underlying interactions between terrestrial algae and their soil-derived microbial communities. Insights from these interactions could also shed light on fundamental ecological principles applicable to broader contexts, such as plant-microbe interactions in agricultural and natural ecosystems. The project's findings promise significant contributions to microbial ecology, evolutionary biology, and potentially sustainable agricultural practices by providing a deeper understanding of microbial symbioses.
This research project aims to deepen our understanding of the ecological and molecular mechanisms underlying interactions between terrestrial algae and their soil-derived microbial communities. Insights from these interactions could also shed light on fundamental ecological principles applicable to broader contexts, such as plant-microbe interactions in agricultural and natural ecosystems. The project's findings promise significant contributions to microbial ecology, evolutionary biology, and potentially sustainable agricultural practices by providing a deeper understanding of microbial symbioses.
During the initial 24 months of the project, we successfully established an extensive culture collection of terrestrial algae from the Eifel National Park, Germany. This collection includes a wide representation of chlorophyte and streptophyte algae, encompassing environmental relatives of the model organism Chlamydomonas reinhardtii and some of the closest extant relatives of land plants. Using these isolates, we developed innovative mesocosm systems designed to study the assembly of microbial communities (phycosphere microbiota) around algae under controlled laboratory conditions.
Through detailed microbial profiling (bacterial, fungal, and other eukaryotic groups), we discovered that algae significantly shape their microbial communities, and these communities differ distinctly based on algal evolutionary relationships. Our research highlighted that algae actively release specific photosynthetically derived compounds and other metabolites that selectively foster beneficial microbial communities, leading to generally mutualistic interactions.
To investigate these interactions further, we conducted advanced transcriptomic and metabolomic analyses on Chlamydomonas reinhardtii grown with soil-derived bacteria. Our findings revealed substantial changes in algal gene expression, notably increased photosynthesis and nutrient transport, coupled with higher release of amino acids that support bacterial growth. This active physiological adjustment by algae, without signs of stress, fundamentally alters the existing perspective that release of photosynthates is primarily an overflow mechanism to sustain the efficiency of the algal photorespiratory mechanism and suggest that the host can perceive the presence of their microbiota member and adjust its responses in order to engage in mutualistic associations.
In collaboration with expert partners, we established the groundwork for genetic screens using a newly developed mutant library of C. reinhardtii. These future genetic screens are aimed at identifying algal genes critical for microbiome interactions, further deepening our understanding of the genetic mechanisms underlying these relationships.
Finally, we established an advanced long-term synthetic ecosystem experiment, continuously cultivating algae and microbial communities under highly controlled laboratory conditions using photobioreactors. This setup, running uninterrupted for over two years, provided unique insights into how environmental factors (such as light intensity) influence community stability and microbial dynamics, validating long-standing ecological theories with empirical data.
Through detailed microbial profiling (bacterial, fungal, and other eukaryotic groups), we discovered that algae significantly shape their microbial communities, and these communities differ distinctly based on algal evolutionary relationships. Our research highlighted that algae actively release specific photosynthetically derived compounds and other metabolites that selectively foster beneficial microbial communities, leading to generally mutualistic interactions.
To investigate these interactions further, we conducted advanced transcriptomic and metabolomic analyses on Chlamydomonas reinhardtii grown with soil-derived bacteria. Our findings revealed substantial changes in algal gene expression, notably increased photosynthesis and nutrient transport, coupled with higher release of amino acids that support bacterial growth. This active physiological adjustment by algae, without signs of stress, fundamentally alters the existing perspective that release of photosynthates is primarily an overflow mechanism to sustain the efficiency of the algal photorespiratory mechanism and suggest that the host can perceive the presence of their microbiota member and adjust its responses in order to engage in mutualistic associations.
In collaboration with expert partners, we established the groundwork for genetic screens using a newly developed mutant library of C. reinhardtii. These future genetic screens are aimed at identifying algal genes critical for microbiome interactions, further deepening our understanding of the genetic mechanisms underlying these relationships.
Finally, we established an advanced long-term synthetic ecosystem experiment, continuously cultivating algae and microbial communities under highly controlled laboratory conditions using photobioreactors. This setup, running uninterrupted for over two years, provided unique insights into how environmental factors (such as light intensity) influence community stability and microbial dynamics, validating long-standing ecological theories with empirical data.
This project has generated significant advances beyond the current scientific understanding. Notably, we demonstrated for the first time that terrestrial algae actively shape their microbiomes through specific metabolic interactions, providing new insights into the mechanistic basis of algal-microbe symbiosis. The integrated use of transcriptomic and metabolomic approaches provides a mechanistic understanding of the molecular dialogue between algae and bacteria, revealing critical pathways by which algae selectively enhance beneficial microbial partnerships.
Moreover, our development of our experimental systems for continuous long-term growth of synthetic phycospheres represents a major methodological innovation, enabling the study of ecological interactions under conditions entirely dependent on algal-produced organic carbon. These findings have substantial implications for understanding microbial ecology and could inform strategies for sustainable agricultural practices, ecosystem management, and soil restoration efforts.
The establishment of a long-term synthetic ecosystem experiment has opened new avenues for ecological research, particularly validating theoretical models of community stability and dynamics. Our empirical data illustrate how specific environmental conditions shape microbial community resilience and complexity.
For the continued success of the proejct, additional research is required, particularly focusing on identifying the genetic factors involved in these interactions and their evolutionary conservation. Additionally, promoting interdisciplinary collaborations and outreach efforts will enhance the broader applicability and impact of these research findings.
Moreover, our development of our experimental systems for continuous long-term growth of synthetic phycospheres represents a major methodological innovation, enabling the study of ecological interactions under conditions entirely dependent on algal-produced organic carbon. These findings have substantial implications for understanding microbial ecology and could inform strategies for sustainable agricultural practices, ecosystem management, and soil restoration efforts.
The establishment of a long-term synthetic ecosystem experiment has opened new avenues for ecological research, particularly validating theoretical models of community stability and dynamics. Our empirical data illustrate how specific environmental conditions shape microbial community resilience and complexity.
For the continued success of the proejct, additional research is required, particularly focusing on identifying the genetic factors involved in these interactions and their evolutionary conservation. Additionally, promoting interdisciplinary collaborations and outreach efforts will enhance the broader applicability and impact of these research findings.