Interdisciplinary Life Science - PULSe Great research is a matter of choice

Louis Sherman

Louis Sherman Profile Picture

Professor of Biological Sciences
Ph.D., University of Chicago, 1970

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Cyanobacteria have become wonderful and versatile model organisms for the study of photosynthesis, nitrogen fixation, hydrogen production and responses to environmental stresses. Our research can help answer questions involved with environmental concerns, alternative energy uses (i.e., solar energy), and health concerns such as microbial toxins and the design of new drugs. The genomic sequence of one favorite cyanobacterium was completed a few years ago, and we now have the task of trying to determine the function of each of its 3,264 genes, ultimately to understand how a cell functions. The lab has successfully constructed microarrays ("gene chips")this is an important technique in biology and all of the genes in an organism can be spotted on a glass slide about the size of a microscope slide. These microarrays are great for studying the activity of genes; this technique, along with the ability to make mutations in virtually every gene, is a key way for determining gene function under different environmental conditions. The genome sequence of another of our favorite cyanobacteria has recently been completed. This unicellular organism shows robust metabolic and circadian rhythms and performs photosynthesis and N2-fixation at different times of the day and night. This organism is key to a large project aimed at understanding the regulation of such processes and the assembly of membrane complexes. The genomes of 6 more Cyanothece species are being sequenced at DOE and will aid us in identifying important genes and processes for alternate energy uses. Our first project concerns environmental stress and membrane assembly. We have constructed a full-genome micraarray for the model organism Synechocystis and we have been studying gene regulation under a variety of environmental conditions. This includes stress conditions, such as nutrient deprivation or oxidative stress, as well as different physiological conditions, such as exponential vs. stationary phases. We are studing some of the key regulatory proteins involved in such transitions, as well as structural and physiological changes to the cell. We are particularly interested in the dynamics of membrane structure and the changes in the Ch1-protein complexes with changes in environmental conditions.

The second major project concerns a unicellular N2-fixing cyanobacterium Cyanothece that we have isolated and purified. In addition, we have now had it's genome sequenced. This strain fixes nitrogen under aerobic conditions either in the light or the dark; it also has a 24-hr periodicity for the peak of nitrogenase activity with a preference for high nitrogenase activity in the dark. These cells also accumulate two inclusion granules; one stores glycogen, the other cyanophycin. Cyanophycin is a nitrogen-storage oligopeptide, composed of asp and arg. We are now investigating the metabolic and regulatory aspects of these cells with special emphasis on the metabolic rhythms established during N2-fixation. These studies include analysis of transcriptional and translational control of nitrogenase and photosynthesis activities, as well as the mechanistic changes that occur in the photosynthetic apparatus throughout the day. Now that the genome has been sequenced, we will also develop a microarray platform and work with collaborators on proteomics analysis. We will study the changes in transcription and translation as a function of time through a 24hr diurnal cycle. In addition, the Cyanothece strains are capable of producing significant quantities of hydrogen and one project is concerned with an understanding of this process and determining ways to make this a useful and cost-effective approach to alternative energy production.

Selected Publications:

Summerfield, T.C., Toepel, J and L.A. Sherman. 2008. Low oxygen induction of normally cryptic psbA genes in cyanobacteria. Biochemistry Rapid Reports. 74:12939-12941.

Summerfield, T. C., Sherman, L. A. 2008. Global transcriptional response of the alkalitolerant cyanobacterium Synechocystis sp. strain PCC 6803 to pH 10. Appl Environ Microbiol. 74:5276-5284.

Welsh, E.A., M. Liberton, J. Stöckel, T. Loh, C. Wang, A.Wollam, R.S. Fulton, S.W. Clifton, J. M. Jacobs, L. A. Sherman, R.D. Smith, R. K. Wilson and H. B. Pakrasi. (2008). The genome of Cyanothece 51142, a unicellular diazotrophic cyanobacterium important in the marine nitrogen cycle. PNAS, 105:15094-15099.

Toepel, J., Welsh, E., Summerfield, T. C., Pakrasi, H. B., Sherman, L. A. 2008. Differential transcriptional analysis of the cyanobacterium Cyanothece sp. strain ATCC 51142 during light-dark and continuous-light growth. J Bacteriol. 190: 3904-3913.

Foster, J. S., Singh, A. K., Rothschild, L. J., Sherman, L. A. 2007. Growth-phase dependent differential gene expression in Synechocystis sp. strain PCC 6803 and regulation by a group 2 sigma factor. Arch Microbiol. 187: 265-279.

Singh, A. K., Sherman, L. A. 2007. Reflections on the function of IsiA, a cyanobacterial stress-inducible, Chl-binding protein. Photosynth Res. 93: 17-25.

Summerfield, T. C., Eaton-Rye, J. J., Sherman, L. A. 2007. Global gene expression of a ”PsbO:”PsbU mutant and a spontaneous revertant in the cyanobacterium Synechocystis sp. strain PCC 6803. Photosynth Res.

Summerfield, T. C., Sherman, L. A. 2007. Role of sigma factors in controlling global gene expression in light/dark transitions in the cyanobacterium Synechocystis sp. strain PCC 6803. J Bacteriol. 189: 7829-7840.

Singh, A. K., Sherman, L. A. 2006. Iron-independent dynamics of IsiA production during the transition to stationary phase in the cyanobacterium Synechocystis sp. PCC 6803. FEMS Microbiol Lett. 256: 159-164.

Singh, A. K., Summerfield, T. C., Li, H., Sherman, L. A. 2006. The heat shock response in the cyanobacterium Synechocystis sp. Strain PCC 6803 and regulation of gene expression by HrcA and SigB. Arch Microbiol. 186: 273-286.

Singh, A. K., Li, H., Bono, L., Sherman, L. A. 2005. Novel adaptive responses revealed by transcription profiling of a Synechocystis sp. PCC 6803 delta-isiA mutant in the presence and absence of hydrogen peroxide. Photosynth Res. 84: 65-70.

Singh, A. K., Sherman, L. A. 2005. Pleiotropic effect of a histidine kinase on carbohydrate metabolism in Synechocystis sp. strain PCC 6803 and its requirement for heterotrophic growth. J Bacteriol. 187: 2368-2376.

Li, H., Singh, A. K., McIntyre, L. M., Sherman, L. A. 2004. Differential gene expression in response to hydrogen peroxide and the putative PerR regulon of Synechocystis sp. strain PCC 6803. J Bacteriol. 186: 3331-3345.

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