Printable Version

Stephen Simkins

Associate Professor
Department of Plant, Soil & Insect Sciences
Stockbridge Hall 12G
University of Massachusetts
Amherst, MA 01003-0910
Tel. (413) 545-5211
ssimkins@pssci.umass.edu

Education

B.S. (Biology), Harvard University, 1977
M.S. (Ecology), Cornell University, 1984
Ph.D. (Environmental Toxicology), Cornell University, 1985
Postdoctoral (Soil Microbiology), Michigan State University and Swedish Agricultural University,1985-1987

Research Interests

Novel approaches to bioremediation
Kinetics of biodegradation of organic toxicants
Microbial population ecology
Spatial variability of soil processes

Research Summary

Biodegradation Kinetics

A wide variety of non-linear models have been developed for the description of patterns of biodegradation of organic compounds that would occur in a host of different environmental circumstances including: i) compounds that support growth of the degradatory microbes in well-mixed environments; ii) compounds that fail to support growth of the organisms that degrade them because of low substrate concentration or intrinsic substrate resistance to metabolic attack; and iii) biodegradation of compounds at low concentrations in poorly-mixed environments, such as soil, in which the need for diffusion of the substrate to the degradatively active cells results in departures from the patterns of biodegradation that are usually observed in well-mixed, active cells results in departures from the patterns of biodegradation that are usually observed in well-mixed, aquatic systems. All of the above models have been evaluated for the description of biodegradation of several model toxicants in pure cultures of bacteria and in samples from natural microbial habitats, such as soil and sewage. Current research efforts in this area focus on the development of models for the kinetics of biodegradation of compounds that are simultaneously attacked by two or more microbial populations differing in affinity for the substrate and in maximum activity per organism.

Microbial Population Ecology

Theoretically necessary conditions for the stable, equilibrium coexistence of two microbialstratins in continuous culture were developed and successfully evaluated with populations Pseudomonas putida and Enterobacter aerogenes growing at the expense of glucose and succinate. Current theoretical research attempts to establish the theoretical condition necessary for the maintenance indynamic equilibrium of more than two populations growing at the expense of a single limiting substrate that is supplied at variable rates. Experimental work in progress is devoted to an evaluation of the importance of population-density-dependent specific death rates of parent strains of bacteria used in genetic engineering when those organisms are introduced into non-sterile soil.

Spatial Variability Of Soil Processes

Techniques for data analysis derived from geostatistics were used to determine that a fraction of the variability of rates of denitrification in arable lands were autocorrelated, i.e., that rates measured at nearby locations tended to be more similar to one another than were rates measured at more widely separated sampling locations. The presence of autocorrelation in the data permits the integrated, using kriging, of this high variable process over a large area from a relatively limited number of rate measurements.

Selected Publications

Perriello, F.A., and S. Simkins. 1999. Biotransformation of trichloroethylene using butane-oxidizing bacteria. J. Soil Contam. 8:117-129.

Ghaemghami, J.,R. S. Baker, and S. Simkins. 1998. Outgassing losses of toluene and m-xylene evaluated by 14C-based mass balances for laboratory bioventing simulations. J. Soil Contam. 7:697-708.

Baker, R. S, J.Ghaemghami, S. Simkins, L. M. Mallory. 1994. Demonstrating the efficacy of bioventing using radiotracers, p. 259-277. In G. W. Gee, N. R. Wing(ed.), In situ remediation: scientific basis for current and future technologies.Battelle Press, Columbus, OH.

Tiedje, J. M.,G. B. Smith, S. Simkins, W. E. Holben, C. Finney, and D. A. Gilichinsky.1994. Recovery of DNA, denitrifiers, and patterns of antibiotic sensitivity in microorganisms from ancient permafrost soils of eastern Siberia, p.83-98. In D. Gilichinsky (ed.), Viable microorganisms in permafrost. Russian Academy of Sciences, Pushchino Research Center, Pushchino, Russia.

Baker, R. S., J.Ghaemghami, S. Simkins, and L. M. Mallory. 1994. A vadose-column treatability test for bioventing applications, p. 32-39. In R. E. Hinchee, B. C. Alleman,R. E. Hoeppel, and R. N. Miller (ed.), Hydrocarbon Bioremediation. Lewis Publishers, Boca Raton, FL.

Groffman, P. M.,J. M. Tiedje, D. L. Mokma, and S. Simkins. 1992. Regional scale analysisof denitrification in north temperate forest soils. Landscape Ecol. 7:45-53.

Klemedtsson, L.,S. Simkins, B. H. Svensson, H. Johnsson, and T. Rosswall. 1991. Soil denitrificationin three cropping systems characterized by differences in nitrogen and carbon supply. II. Water and NO3- effects on the denitrification process.Plant Soil 138:273-286.

Mahinakhbarzadeh,M., S. Simkins, and P. L. M. Veneman. 1991. Spatial variability of organic matter content in selected Massachusetts map units, p. 231-242. In M. J. Mausbach and L. P. Wilding (ed.), Spatial variability of soils and landforms. Soil Sci. Soc. Am., Madison, WI.

Svensson, B. H.,L. Klemedtsson, S. Simkins, K. Paustian, and T. Rosswall. 1991. Soil denitrification in three cropping systems characterized by differences in nitrogen and carbon supply. I. Rate- distribution frequencies, comparison between systemsand seasonal N losses. Plant Soil 138:257-271.

Christensen, S.,S. Simkins, and J. M. Tiedje. 1990. Spatial variation in denitrification: dependency of activity centers on the soil environment. Soil Sci. Soc. Am. J. 54:1608-1613.

Christensen, S.,S. Simkins, and J. M. Tiedje. 1990. Temporal patterns of soil denitrification:their stability and causes. Soil Sci. Soc. Am. J. 54:1614-1618.

Tiedje, J. M.,S. Simkins, and P. M. Groffman. 1989. Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods,p. 217-240. In M. Clarholm and L. Bergstrîm (ed.), Ecology of arable land.Kluwer Academic Publishers.

Schimel, D.S.,S. Simkins, T. Rosswass, A.R. Mosier, and W.J. Parton. 1988. Scale and the measurement of nitrogen-gas fluxes from terrestrial ecosystems, p.179-193. In T. Rosswall and R.G. Woodmansee, and P.G. Risser (ed.), Scalesand global change. John Wiley and Sons, New York.

Klemedtson, L.,S. Simkins, and B.H. Svensson. 1986. Tandem thermal-conductivity and electron-capture detectors and non-linear calibration curves in quantitative nitrous oxideanalysis. J. Chromatogr. 361:107-116.

Schmidt, S.K.,S. Simkins, and M. Alexander. 1985. Models for the kinetics of biodegradation of organic compounds not supporting growth. Appl. Environ. Microbiol. 50:323-331.

Scow, K.M., S.Simkins, and Mr. Alexander. 1986. Kinetics of mineralization of organicc ompounds at low concentrations in soil. Appl. Environ. Microbiol. 51:1028-1035.

Simkins, S., R.Mukherjee, and M. Alexander. 1986. Two approaches to modeling kineticsof biodegradation by growing cells and application of a two-compartment model for mineralization kinetics in sewage. Appl. Environ. Microbiol.51:1153-1160.

Simkins, S., and M. Alexander. 1985. Nonlinear estimation of the parameters of Monod kinetics that best describe mineralization of several substrate concentrations bydissimilar bacterial densities. Appl. Environ. Microbiol. 50:816-824.

Simkins, A., and M. Alexander. 1984. Models for mineralization kinetics with the variables of substrate concentration and population density. Appl. Environ. Microbiol.47:1299-1306.