This information applies to pages in the CSUN template system.Windows-press ALT + an access key. Macintosh-press CTRL + an access key.
Ph.D. University of California at Davis
The research in my laboratory focuses on the problem of how bacteria regulate adaptive alterations of their cell morphology and physiology in response to environmental changes. I utilize the cyanobacterium Nostoc punctiforme for these studies. This filaments cyanobacterium can differentiate from normal vegetative cells into nitrogen fixing heterocysts, resistant akinetes, or motile hormogonia, that move by gliding motility. Our research focuses on identification of genes involved in cellular differentiation of akinetes. Akinetes are resting cells capable of surviving long periods of desiccation and cold that differentiate from normal vegetative cells due to low light or phosphate starvation.
We have developed a model system allowing the study of synchronously induced akinetes in this organism using a metabolic mutant lacking glucose-6-phosphate dehydrogenase (encoded by the zwf gene). The cells of this mutant synchronously turn into akinetes after several days in the dark if given a carbon source such as fructose. Use of our model system in conjunction with DNA microarray analysis has allowed us to identify putative genes thought to be involved in akinete development. Students are involved in mapping the transcriptional start sites, confirming akinete-specific gene expression using transcriptional reporter plasmids, and mutating the genes to see if akinete formation or function are affected.
Results of these studies should provide insights about regulation of cellular differentiation, and mechanisms by which bacteria can survive harsh environmental conditions. Please visit our web site to download publications relevant to this work, see the students involved in this research, or to obtain more details about this project.
Additional Academic History:
1995-98 Postdoctoral Research Associate: Physiology and genetics of phosphorous metabolism in free-living and symbiotic rhizobia, Montana State University, Bozeman, MT
NIH-SCORE Grant, Genomic Characterization of Akinete Differentiation, $509.539 (7/06 to 6/10), PI. The overall goals are to use DNA microarray analysis to identify genes involved in the differentiation of vegetative cells into cyanobacterial akinetes and to determine their function.
Holmquist, C.P., G.P. Holmquist, and M.L. Summers. 2011. Comparing binding site information to binding affinity reveals that Crp/DNA complexes have several distinct binding conformers. Nucleic Acids Research 39: 6813-24
Kaplan-Levy, R.N.; O., Hadas; M.L., Summers; J., Rücker; A., Sukenik. 2010. Akinetes: Dormant Cells of Cyanobacteria. Dormancy and resistance in harsh environments. E. Lubzens, J. Cerdà and M. Clark (Eds.), Topics in Current Genetics, Vol. 21. Springer-Verlag Berlin Heidelberg
Hedger, J , P.C. Holmquist, K.A. Leigh, K. Saraff, C. Pomykal, and M.L. Summers. 2009. Illumination stimulates cAMP receptor protein dependent transcriptional activation from regulatory regions containing type I, and II promoter elements in Synechocystis sp. PCC 6803. Microbiology 155: 2994-3004
Campbell, E.L., M.L. Summers, H. Christman, M.E. Martin, and J.C. Meeks. 2007. Global gene expression patterns of Nostoc punctiforme in steady state dinitrogen-grown heterocyst-containing cultures and at single time points during the differentiation of akinetes and hormogonia. Journal of Bacteriology 189:5247-5256.
Argueta, C., K. Yuksek, R. Patel, and M.L Summers. 2006. Identification of Nostoc punctiforme akinete-expressed genes using differential display. Molecular Microbiology 61:748-757.
Argueta, C and M.L. Summers. 2005. Characterization of a model system for the study of Nostoc punctiforme akinetes. Archives of Microbiology 183:338-346.
Argueta, C., K. Yuksek, and M.L. Summers. 2004. Construction and use of GFP reporter vectors for analysis of cell-type-specific gene expression in Nostoc punctiforme. Journal of Microbiological Methods 59:181-188.
Meeks, J.C., E.L. Campbell, M.L. Summers, F.C. Wong. 2002. Cellular differentiation in the cyanobacterium Nostoc punctiforme. Archives of Microbiology 178:395-403.
Summers, M.L., L. M. Botero, S.C. Busse, and Timothy R. McDermott. 2000. The Sinorhizobium meliloti Lon protease is involved in regulating exopolysaccharide synthesis and is required for nodulation of alfalfa. Journal of Bacteriology 182:2551-2558.
Summers, M.L., M.C. Denton, T.R. McDermott. 1999. Genes coding for phosphotransacetylase and acetate kinase in Sinorhizobium meliloti are in an operon that is inducible by phosphate stress and controlled by PhoB. Journal of Bacteriology 181:2217-24.
Summers, M.L., and J.C. Meeks. 1996. Transcriptional regulation of zwf, encoding glucose-6-phosphate dehydrogenase, from the cyanobacterium Nostoc punctiforme strain ATCC 29133. Molecular Microbiology 22:473-480.
Summers, M.L., J.G. Wallis, E.L. Campbell, and J.C. Meeks. 1995 Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133. Journal of Bacteriology 177:6184-6194.
Summers, M.L., J.C. Meeks, S. Chu, and R.E. Wolf, Jr. 1995. Nucleotide sequence of an operon in Nostoc sp. strain ATCC 29133 encoding four genes of the oxidative pentose phosphate cycle. Plant Physiology 107: 267-268.