John A. Berges Associate Professor BSc University of Guelph 1987 MSc University of Guelph 1989 PhD University of British Columbia 1994 Postdoctoral Fellow Brookhaven National Laboratory 1994-6 Lecturer Queen's University of Belfast 1996-2002	Office: Lapham 587 Phone: 414-229-3258 FAX: 414-229-3926 Email: berges@uwm.edu Personal Homepage Electronic Reserve Materials:
Phytoplankton and Zooplankton Ecophysiology and Biochemistry

Research Interests

1) Developing indices of growth and other biological rates In all ecosystems, but particularly in the oceans, accurate estimates of biological rates (e.g. photosynthesis, respiration, nutrient uptake, grazing, degradation and remineralization) are essential to understanding biogeochemical cycles, and predicting patterns of organic production. Furthermore, such processes may be sensitive indicators of environmental damage and so provide early warnings of potential problems. Unfortunately, such rates are extremely difficult to measure in field settings. My research has focused on examining biochemical indices, particularly enzyme activities, as means of predicting different rates of nitrogen assimilation and growth in photoautotrophs, and respiration, excretion and growth in microcrustaceans . As well I have examined cell death and protein degradation by looking at the induction of endocellular proteases in marine phytoplankton using assays of enzyme activity, protein electrophoresis and immunochemistry. Work on algal cell death and stress responses has been applied in marine communities during differing stages of blooms. 2) Characterizing cellular acclimation The range of acclimations that cells make to environmental changes is extensive: from changes in composition to alterations in biochemistry (e.g. enzyme levels) to changes in morphology. This area of research is critical in understanding how environmental changes will affect different organisms and in understanding which variables constrain populations. I have examined the acclimation of nitrogen uptake to supply using this approach, and also the reprocessing of nitrogen through the induction of endocellular proteases that occurs during exhaustion of nitrogen, or transitions to darkness. Furthermore, differences between the responses of phytoplankton to chemostat-style nitrogen limitation versus deprivation of nutrients are highly relevant to oceanographic question, yet have received little attention. A sideline to research in acclimation involves the examination of stress response proteins (some of which are proteases) in algae as indicators of marine pollution. 3) Clarifying the size-dependence of cellular processes Size is probably the single most obvious feature of an organism, and it profoundly affects structure and function. Oceanographers implicitly recognize this; planktonic organisms have been divided into size categories from early descriptive studies. Virtually every biochemical and physiological process (including respiration and photosynthesis) shows some degree of allometric scaling with organism size. Defining size-dependencies is particularly important since recent models of planktonic processes have tried to incorporate size-scaling of metabolism with only rudimentary understanding. I have examined the question of scaling of enzyme activity with size in zooplankton, and am extending this work to phytoplankton carbon fixation and nitrogen uptake by examining the size-dependence of these processes simultaneously at the level of macroscopic rates, enzyme activities and quantities, and rates of translation and transcription.

Selected Publications

Berges, J. A., D. J. Franklin, and P. J. Harrison. 2001. Evolution of an artificial seawater medium: improvements in ESAW over the last two decades. J. Phycol. 37: 1-8. Boyd, P. W., N. D. Sherry, J. A. Berges, J. K. B. Bishop, S. E. Calvert, M. A. Charette, S. J. Giovannoni, R. Goldblatt, P. J. Harrison, S. B. Moran, S. Roy, M. Soon. 1999. Transformations of biogenic particulates from the pelagic to the deep ocean realm. Deep-Sea Research 46: 2761-2792. Vergara, J. J., J. A. Berges, and P. G. Falkowski. 1998. Diel periodicty of nitrate reductase activity and protein levels in the marine diatom Thalassiosira weissflogii (Bacillariophyceae). J. Phycol. 34: 952-961. Boyd, P., J. A. Berges and P. J. Harrison. 1998. In vitro iron enrichment experiments at iron-rich and -poor sites in the NE subarctic Pacific. J. Exp. Mar. Biol. Ecol. 227: 133-151. Berges, J. A. and P. G. Falkowski. 1998. Physiological stress and cell death in marine phytoplankton: induction of proteases in reponse to nitrogen- or light-limitation. Limnol. Oceanogr. 43: 129-135. Berges, J. A. 1997. Miniview: algal nitrate reductases. Eur. J. Phycol. 32: 3-8. Berges, J. A., D. O. Charlebois, D. C. Mauzerall, and P. G. Falkowski. 1996. Differential effects of nitrogen limitation on photosynthetic efficiency of Photosystems I and II in microalgae. Plant. Physiol. 110: 689-696.