A day in the life of Chlamydomonas and its neighbors: Systems analysis of a microbial phototroph-heterotroph symbiosis
EMSL Project ID
60010
Abstract
Phytoplankton, which rely on the sun for energy, are responsible for roughly half of global primary productivity. These organisms dramatically change their metabolic strategy in the night when sunlight energy is unavailable. While we have a clear picture of algal physiology and metabolism in axenic culture, we know very little about how diurnal cycles impact the trophic exchanges of the microbial world. Thus, our understanding of algal ecophysiology and the flow of carbon and other nutrients in the natural environment is incomplete. Here, we will use the reference chlorophyte Chlamydomonas reinhardtii and the vitamin B12-producing ⍺-proteobacterium Mesorhizobium loti to distinguish the dynamics and nutrient exchanges in a microbial phototroph-heterotroph symbiosis. The prevailing view is that bacteria receive reduced carbon from the alga, and the alga in turn receives vitamin B12 from the bacterium. From our previous work with highly synchronous axenic cultures of C. reinhardtii, we hypothesize that the quantity and forms of reduced carbon made available to sympatric microbial heterotrophs will change in the day and the night. We would like to test this hypothesis using JGI’s high-throughput metabolomics and untargeted analysis platform to monitor C. reinhardtii’s extracellular and intracellular metabolite profile with high temporal resolution over a diurnal cycle. Furthermore, we will test M. loti’s preference for daytime and nighttime algal substrates using exometabolomics with JGI. In addition, the genetic mechanisms underlying successful symbiosis during day/night cycles are not known. We propose to use RNAseq at JGI and proteomics at EMSL to discern changes in gene expression and protein accumulation in both alga and bacterium as they continuously adjust to changes in each other’s metabolic strategies during diel growth. In a previous project, we described changes in the transcriptome and proteome over a diurnal period in axenic synchronized Chlamydomonas cells. We will assess whether the diurnal transcriptome and proteome programs are modified by the presence of M. loti, and conversely whether diurnal metabolic cycling constrains the bacterium’s physiology. These experiments will be in the context of parallel measurements of photosynthesis, respiration, cell division, and vitamin B12 production in the coculture performed in our own laboratory. In summary, we will obtain a systems-level view to address basic questions about the timing, quantity and identity of mutualistic exchanges between alga and bacterium during a typical symbiotic association in nature. This work will exploit a system with reduced complexity, established reference organisms with well-described physiologies, and a suite of associated proven methodologies to improve our understanding of trophic interactions and diel patterns in the microbial world. EMSL and JGI's technical and computational expertise with environmental samples containing multiple organisms is critical for the success of this project. In addition, the existing infrastructure and datasets from past projects on Chlamydomonas with multiple different laboratories will facilitate data analysis and comparisons. This new endeavor in our laboratory is supported for the duration of the requested project period by the Moore Foundation, which ensures the availability of personnel and supplies for sample generation and data analysis.
Project Details
Project type
FICUS Research
Start Date
2021-10-01
End Date
2023-12-08
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members