Project Details
Description
Chlorophototrophs, (bacterio)-chlorophyll [(B)-Chl]-dependent phototrophs, perform photosynthesis, the fundamental biological process that permits life to exist on Earth. These organisms efficiently capture and convert light energy into chemical potential energy that is subsequently used to fix CO2 into biomass. This proposal mostly focuses on 'green bacteria,' organisms that synthesize millions of BChl c, d, or e molecules per cell, which self-assemble into supramolecular structures in chlorosomes. A single chlorosome can contain up to 250,000 BChl c, d, or e molecules, and thus chlorosomes allow some green bacteria to grow in remarkably low light niches—where a single Chl molecule might only absorb 1 to 10 photons per day. Green bacteriaare important primary producers in many anoxic environments, and they contribute significantly to the biogeochemical cycling of carbon, nitrogen, and sulfur on Earth.The long-term objectives of this research program are to understand the design principles of chlorosomes, and how those principles impact their structure, function, and biogenesis.Because BChls c, d, and e spontaneously assemble into supramolecular aggregates without a protein scaffold, the lessons learned from chlorosomes can be exploited in biomimetic systems. To maximize the utility of such systems, however, it is important to understand the underlying physico-chemical rules that define the structural and functional principles for these structures. Thus, we seek to understand how the complexity of chlorosome components—which include extensive modifications of BChl side chains and esterifying alcohols; carotenoid diversity; the presence and function of quinones, glycolipids, wax esters, and the proteins of the chlorosome envelope—contribute to chlorosome functionality. When appropriate (e.g., for Chloracidobacterium thermophilum), we also seek to understand other components of the photosynthetic apparatus, e.g., the reaction centers (RCs), that transduce absorbed light into chemical energy.We are studying chlorosomes and Type-1 RCs in organisms from very different environmental niches: Chlorobaculum tepidum and Cba. limnaeum are strict anaerobes that occur in anoxic, sulfide-rich environments. Cab. thermophilum is a microaerophilic photoheterotroph that we identified and isolated in axenic culture, and it has chlorosomes that differ in many ways from those of Cba. tepidum. Cab. thermophilum also has unusual, oxygen-tolerant RCs that contain three types of Chl: Chl a, BChl a, and Zn-BChl a¢. Finally, we are currently attempting to isolate 'Candidatus Thermochlorobacter aerophilum,' a fully aerobic member of the phylum Chlorobi, which is also a photoheterotroph with a photosynthetic apparatus similar to that of Cab. thermophilum. The very different oxygen relationships of these organisms, and differences in their Type-1 RCs, FMO, and chlorosomes, can provide insights into how the basic system can adapt to cope with different light and oxygen concentrations.Comparisons of the properties of chlorosomes and homodimeric Type-1 RCs of organisms inhabiting anoxic (Cba. tepdium and Cba. limnaeum) and oxic (Cab. thermophilum and 'Ca. Tcb. Aerophilum') environments will reveal important adaptations of chlorosomes to these two very different niches and will provide new information about the evolution of photosynthesis as well as the design principles for artificial photosynthesis.
Status | Finished |
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Effective start/end date | 11/1/15 → 10/31/20 |
Funding
- Basic Energy Sciences: $4,066,887.00
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