Biochemistry and Molecular Biology
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Donald Bryant

Donald Bryant

Main Content

  • Ernest C. Pollard Professor in Biotechnology and
  • Professor of Biochemistry and Molecular Biology
403C Althouse Laboratory
University Park, PA 16802
Phone: (814) 865-1992

Research Interests

Physiology, biochemistry, genetics, and genomics of photosynthetic bacteria

Graduate Programs


Research Summary

Genomics, structural and functional relationships, metabolism, physiology and ecology of chlorophototrophic bacteria

Photosynthesis, the chlorophyll-dependent conversion of light energy into chemical energy with the ensuing reduction of carbon dioxide to biomass, is arguably the most important biological process on Earth. Among prokaryotes, the ability to use chlorophylls to capture and convert light into biochemical energy was until very recently believed to occur in members of only five eubacterial kingdoms: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, and Firmicutes. We recently discovered a previously unknown chlorophototroph, Chloracidobacterium thermophilum, which is a member of the poorly characterized kingdom Acidobacteria ( We have succeeded in isolating this organism in axenic culture, and have shown that it is a phototroph that requires all three branched chain amino acids, lysine, bicarbonate, and vitamin B12 for growth. We have also recently learned that the homodimeric reaction centers in this organism likely employ Zn-BChl a' as the special pair.

Current research in my laboratory focuses on a wide variety of topics in photosynthesis, including structure-function relationships of proteins, biogenesis of the photosynthetic apparatus, gene regulation, and photosynthetic physiology. We principally study two model organisms, the unicellular, euryhaline cyanobacterium Synechococcus sp. PCC 7002 and the moderately thermophilic green sulfur bacteria Chlorobaculum tepidum and Chlorobaculum phaeobacteroides (Chlorobi), which can easily be manipulated genetically. Because Cyanobacteria perform oxygen-evolving photosynthesis but characterized Chlorobi are obligately photoautotrophic anaerobes, these two organisms provide an interesting contrast in physiology and metabolism. We additionally study natural phototrophic communities in Yellowstone National Park (Figure 1).


Dr. Bryant research Figure 1 image

Figure 1. Mushroom Spring (A) and Panel Octopus Spring (B), alkaline siliceous hot springs in the Lower Geyser Basin of Yellowstone National Park, WY. The inset panel (C) is a section of the microbial mat showing the upper, 1-2 mm green chlorophototrophic community from which Chloracidobacterium thermophilum was isolated. The lower red layer from about 2-5 mm below the surface are predominantly carotenoid-containing members of Roseiflexus spp. in the anoxic/microoxic community.

Long-term objectives of my laboratory are to understand the structure, function, assembly, and regulation of expression of bacterial photosynthetic apparatuses, principally those of members of the phyla Cyanobacteria and Chlorobi. To achieve these goals, we have obtained complete genomic sequences for all of the organisms we study (about 80 organisms in total, including genomes for ecological species of Synechococcus spp. and Cab. thermophilum. We additionally use nextGen RNA sequencing methods for transcription profiling of Synechococcus sp. PCC 7002, Cba. tepidum, as well as for profiling gene expression patterns of the entire mat community from which Cab. thermophilum was isolated (see Figure 1). In a recent Multi-omics Analysis Experiment (MOAE, or the “Mother Of All Experiments”), >15,000 genes were tracked in samples collected at hourly intervals over a full diurnal cycle.  We have also recently analyzed the composition of the anoxic undermat community of these mats ( see )

The photosynthetic apparatus of cyanobacteria closely resembles that found in the chloroplasts of higher plants. We have developed sophisticated genetic tools to analyze gene function in Synechococcus sp. PCC 7002, and these have been used for metabolic engineering to improve biosolar hydrogen, biomass, and biofuels production in this robust cyanobacterium. We recently discovered that some cyanobacteria can acclimate and grow in far-red light, a process we named Far-Red Light Photoacclimation (FaRLiP). This acclimation process leads to extensive remodeling of the photosynthetic apparatus and the synthesis of far-red light-absorbing pigments, including chlorophylls d and f, as well as special phycobiliproteins that absorb far-red light ( ). In even more recent studies, we established functional genetic systems in four organisms that can perform FaRLiP, including Chlorogloeopsis fritschii PCC 9212 and Synechococcus sp. PCC 7335, and identified the enzyme that converts chlorophyll a into chlorophyll f (Ho et al., (2016) Science, in press, doi: 10.1126/science.AAF9178).

The Chlorobi are specifically adapted for survival in low-light environments and are important in reducing carbon and nitrogen while oxidizing sulfide in anoxic environments. We have developed a reliable natural transformation method for Chlorobaculum tepidum and have used this capability to define the pathways for bacteriochlorophyll and carotenoid biosynthesis in this organism as well as to characterize the structure of bacteriochlorophylls in the light-harvesting organelle, the chlorosome (Figure 2).


Bryant figure 2

Figure 2. Single and double-layer model of bacteriochlorophyll d structure in chlorosomes of a bchQRU mutant of Chlorobaculum tepidum. See and ).

Students and postdoctoral associates apply a broad combination of methods including microbial ecology, microbial physiology, genomics and bioinformatics, molecular genetics, protein biochemistry, and spectroscopic methods. We collaborate extensively with Dr. John H. Golbeck ( ) and Dr. David M. Ward of Montana State University (see NSF, DOE, NASA, and Penn State University currently provide financial support for our research. Professor Bryant is also a member of the Photosynthetic Antenna Research Center (PARC), a multi-investigator/multi-university DOE-sponsored Energy Frontier Research Center centered at Washington University in St. Louis. More detailed information about the research projects in my laboratory can be found through our recent publications.


pdf file CV of Dr. Donald Bryant (PDF)

Selected Publications

Publications from 2016:

  • Ho, M.-Y., Shen, G., Canniffe, D. P., Zhao, C., and Bryant, D. A. 2016. Light-dependent chlorophyll f synthase is a highly divergent paralog of PsbA of Photosystem II. Science, in press. doi: 10.1126/science.AAF9178.
  • Günther, L., Jendrny, M., Bloemsma, E. A., Tank, M., Oostergetel, G. T., Bryant, D. A., Knoester, J. and Köhler, J. 2016. Structure of light-harvesting aggregates in individual chlorosomes. J. Phys. Chem. B, in press. doi: 10.1021/acs.jpcb.6b03718.
  • Thiel, V., Wood, J. M., Olsen, M. T., Ward, D. M., and Bryant, D. A. 2016. The dark side of the Mushroom Spring microbial mat: life in the shadow of chlorophototrophs. Part 1: Microbial diversity based on 16S rRNA amplicon and metagenome sequencing. Front. Microbiol. 7, 919.
  • Tank, M., Thiel, V. Ward, D. M. and Bryant, D. A. 2016. A panoply of phototrophs: a photomicrographic overview of chlorophototrophs found in the microbial mats of alkaline siliceous hot springs in Yellowstone National Park, WY, USA. In: “Modern Topics in the Phototrophic Prokaryotes: Environmental and Applied Aspects,” (Hallenbeck, P. C., ed.), Springer, Berlin, in press.
  • Llorens-Marès, T., Liu, Z., Allen, L. Z., Rusch, D. B., Craig, M. T., Dupont, C. L., Bryant, D. A. and Casamayor, E. O. 2016. Speciation and ecological success by horizontal gene transfer in a green sulfur bacterial population: evidence for virus-mediated gene transmission. ISME J., in press.
  • Bernstein, H. C., McClure, R. S., Hill, E. A., Markillie, L. M., Romine, M. F., Posewitz, M. C., Bryant, D. A., Konopka, A., Fredrickson, J. K., and Beliaev, A. S. 2016. Unlocking the constraints of cyanobacterial productivity: adaptations enabling ultrafast growth. mBio, in press.
  • Tsukatani, Y., Mizoguchi, T., Thweatt, J., Tank, M., Bryant, D. A. and Tamiaki, H. 2016. Glycolipid analyses of light-harvesting chlorosomes from envelope protein mutants of Chlorobaculum tepidum. Photosynth. Res. 128, 235-241. doi: 10.1007/s11120-016-0228-z
  • Qian, X., Kumaraswamy, G. K., Zhang, S., Gates, C., Ananyev, G. M., Bryant, D. A., and Dismukes, G. C. 2016. Inactivation of nitrate reductase alters metabolic branching of carbohydrate fermentation in the cyanobacterium Synechococcus sp. PCC 7002. Biotechnol. Bioeng. 113, 979-988. doi: 10.1002/bit.25862
  • Krishnan, A., Zhang, S., Liu, Y., Bryant, D. A. and Dismukes, C. G. 2016. Consequences of ccmR deletion on respiration, fermentation and H2 metabolism in cyanobacterium Synechococcus sp. PCC 7002. Biotechnol. Bioeng. 113, 1448-1459. doi: 10.1002/bit.25913
  • Klotz, M. K., Bryant, D. A., Fredrickson, J. K., Inskeep, W. P. and Kühl, M. 2016. Systems Biology and Ecology of Microbial Mat Communities. Front. Microbiol., e-book, 262 pp. doi: 10.3389/978-2-88919-793.4
  • Klotz, M. K., Bryant, D. A., Fredrickson, J. K., Inskeep, W. P. and Kühl, M. 2016. Systems biology and ecology of microbial mat communities. Editorial. Front. Microbiol. 7, 115. 2
  • Shen, G., Gan, F., and Bryant, D. A. 2016. The siderophilic cyanobacterium Leptolyngbya sp. strain JSC-1 acclimates to iron starvation by expressing multiple isiA-family genes. Photosynth. Res. 128, 325-340. doi: 10.1007/s11120-016-0257-7
  • Xia, S., Cartron, M., Morby, J., Bryant, D. A., Hunter, C. N., and Leggett, G. J. 2016. Fabrication of nanometer and micrometer scale protein structures by site-specific immobilization of histidine-tagged proteins to aminosiloxane films with photoremovable protein-resistant protecting groups. Langmuir 32, 1818-1827. doi: 10.1021/acs.langmuir.5b04368
  • Bernstein, H. C., McClure, R. S., Thiel, V., Overall, C. C., Sadler, N. C., Kim, Y.-M., Chrisler, W. B., Charania, M. A., Hill, E. A., Bryant, D. A., Romine, M. F., Jansson, J. K., Fredrickson, J. K., and Beliaev, A. S. 2016. Acclimation and response to partnership in a metabolically coupled phototroph-heterotroph consortium, ISME J., revision submitted.
  • McClure, R. S., Overall, C. C., McDermott, J. E., Hill, E., Markille, L. M., McCue, L. A., Taylor, R. C., Ludwig, M., Bryant, D. A., and Beliaev, A. S. 2016. Linking transcriptomic organization to the regulatory landscape of cyanobacteria through co-expression network analysis. Nucl. Acids Res., revision submitted.
  • Peréz, A. A., Liu, Z., Rodionov, D. A., Li, Z., and Bryant, D. A. 2016. Complementation of cobalamin auxotrophy in Synechococcus sp. PCC 7002 and validation of a putative cobalamin riboswitch in vivo. J. Bacteriol., revision submitted.
  • Peréz, A. A., Rodionov, D. A., and Bryant, D. A. 2016. Characterization of cobalamin transport in the cyanobacterium Synechococcus sp. PCC 7002. J. Bacteriol., revision submitted.
  • Zhang, S., Qian, X., Chang, S., Dismukes, G. C. and Bryant, D. A. 2016. Reconstructing the tricarboxylic acid cycle in a cyanobacterium: introduction of the GABA shunt into the cyanobacterium Synechococcus sp. PCC 7002. Biotechnol. Bioeng., submitted for publication.
  • Ho, M.-Y., Gan, F., Shen, G., Zhao, C., and Bryant, D. A. 2016. Far-red light photoacclimation (FaRLiP) in the Synechococcus sp. PCC 7335. I. Regulation of FaRLiP gene expression. Photosynth. Res., submitted for publication.
  • Ho, M.-Y., Gan, F., Shen, G., and Bryant, D. A. 2016. Far-red light photoacclimation (FaRLiP) in the Synechococcus sp. PCC 7335. II. Characterization of phycobiliproteins produced during acclimation to far-red light. Photosynth. Res., submitted for publication.