Bi 475/575 FRESHWATER ECOLOGY SPRING TERM, 2008
Since joining the faculty of Biology at the University of Oregon, Dr. Castenholz has been active in research with support mainly from the NSF and NASA. After working on the seasonal ecology of freshwater and marine diatoms, he switched in the middle 1960's, almost completely, to the community ecology and physiological ecology of photosynthetic bacteria of hot springs, cyanobacteria primarily, but also non-oxygen producing phototrophs with the discovery in his lab of the new genera, Chloroflexus and Heliothrix which became the basis for a new phylum, the Chloroflexi.
Later research developed into a study of phototrophic prokaryotes in microbial mats of hypersaline marine and freshwater habitats, including Antarctic mats dominated by cyanobacteria. The research questions asked include: How do various microorganisms tolerate and adapt to environmental extremes? These extremes include high and low temperature, low pH, high salinity and desiccation, toxic levels of sulfide, and high solar irradiance. A long-term project has been an evaluation of the adaptive value of responses by cyanobacteria to high UV-radiation, in the context of natural habitats. In these studies, the Castenholz lab team has identified and characterized scytonemin, a UV-sunscreen pigment in sheaths surrounding many highly exposed cyanobacteria, and they have demonstrated the importance of this compound in increasing fitness. They have also shown a vital, vertical escape response of motile cyanobacteria to UV radiation in microbial mats, both in temperate and polar environments.
Throughout the last 25 years, Dr. Castenholz has also been involved in trying to unravel the confusion in cyanobacterial taxonomy and classification. He served as co-editor and coordinator for the phototrophic sections and a co-author of portions of this subject in Volume One of the second edition of the Bergey's Manual of Systematic Bacteriology (2001). In addition, he has established a culture collection of cyanobacteria from many locations and habitats, including a large number of isolates from hot springs (alkaline and acidic) over much of the globe, from hypersaline waters, and from polar freshwater habitats. The culture collection now contains over 1,200 strains and is named the Culture Collection of Microorganisms from Extreme Environments (CCMEE).
Research in the Castenholz Lab is currently focused on three areas:
Selected Recent Publications:
Miller, S.R., Castenholz, R.W. and Pedersen, D. (2007) Phylogeography of the thermophilic cyanobacterium Mastigocladus cf. laminosus. Appl. Environ. Microbiol. (in press)
Fleming, E.D. and Castenholz, R.W. (2007) Effects of periodic desiccation on the synthesis of the UV-screening compound, scytonemin, in cyanobacteria. Environ. Microbiol. 9:1448-1455.
Roeselers, G., Norris, T.B., Castenholz, R.W., Rysgaard, S., Glud, N., Kühl, M. and Muyzer, G. (2007) Diversity of phototrophic bacteria in microbial mats in Arctic hot springs (Greenland). Environ. Microbiol. 9: 26-38.
Fleming, E. D., Bebout, B. M., and Castenholz, R.W. (2007) Effects of salinity and light intensity on the resumption of photosynthesis in a rehydrated cyanobacterial mat from Baja California Sur, Mexico. J. Phycol. 43:15-24.
Lehr, C.R., Frank, S.D., D’Imperio, S., Kalinin, A.V, Toplin, J.A., Norris T.B., Castenholz, R.W., and McDermott, T.R. (2007). Cyanidial (Cyanidiales) Population Diversity and Dynamics in an Acid-Sulfate Chloride Spring in Yellowstone National Park. J. Phycol. 43: 3-14.
Castenholz, R.W. and Norris, T.B. (2005) Revisionary concepts of species in the cyanobacteria and their applications. Algological Studies117: 53-69.
Norris, T.B. and Castenholz, R.W. (2005) Effects of environmental stressors on photosynthetic microorganisms in geothermal springs of Yellowstone National Park. In : Inskeep, W.P. (Ed.), Geothermal Biology and Geochemistry in Yellowstone National Park. Thermal Biology Institute, Montana State University, Bozeman, MT pp. 1-13.
Castenholz, R.W. (2004) Phototrophic bacteria under UV stress. In : Seckbach, J. (Ed.) Origins, Evolution and Biodiversity of Microbial Life. Kluwer Acad. Publ., Dordrecht, pp.445-461.
Dillon, J.G. and Castenholz, R.W. (2003) The synthesis of the UV-screening pigment, scytonemin, and photosynthetic performance in isolates from closely related populations of cyanobacteria (Calothrix sp.). Environmental Microbiology. 5 : 484-491.
Dillon, J.G., Miller, S.R. and Castenholz, R.W. (2003) UV-acclimation responses in natural populations of cyanobacteria (Calothrix sp.) Environmental Microbiology 5 : 473-483.Norris T.B., McDermott, T.R. and Castenholz, R.W. (2002) The long-term effects of UV exclusion on the microbial composition and photosynthetic competence of bacteria in hot spring microbial mats. FEMS Microbiol. Ecol. 39 :193-209.
Miller, S.R. and Castenholz, R.W. (2001) Ecological physiology of Synechococcus sp.Strain SH-94-5, a naturally occurring cyanobacterium deficient in nitrate assimilation. Applied & Environmental Microbiology 67 : 3002-3009.
Castenholz, R.W. (2001) Cyanobacteria et al. In : Boone, D.R., Castenholz, R.W., and Garrity, G.M. (Eds.) (2001) Bergey’s Manual of Systematic Bacteriology, 2nd Ed., Vol. 1. The Archaea and the Deeply Branching and Phototrophic Bacteria. Springer -Verlag, NY. pp.473-597 (various sections with other first authors).
Ward, D.M. and Castenholz, R.W. (2000) Cyanobacteria in geothermal habitats. In: Ecology of Cyanobacteria: Their Diversity in Time and Space (Whitton, B. A. and Potts, M., eds.), Kluwer Acad. Publ., Dordrecht, pp. 37-59.
Castenholz, R.W. and Garcia-Pichel, F. (2000) Cyanobacterial responses to UV-radiation. In: Ecology of Cyanobacteria: Their Diversity in Time and Space (Whitton, B. A. and Potts, M., eds.), Kluwer Acad. Publ., Dordrecht, pp. 591-611.
Nadeau, T-L and Castenholz, R.W. (2000) Characterization of psychrophilic oscillatorians (Cyanobacteria) from Antarctic meltwater ponds. J. Phycol. 36: 914-923.
Miller, S.R. and Castenholz, R.W. (2000) The evolution of thermotolerance in hot spring cyanobacteria of the genus Synechococcus. Applied & Environmental Microbiology 66: 4222-4229.