Martin Aksel Hjortsø
	George H. Nusloch II Professor M.S., The Technical University of Denmark, 1978 Ph.D., University of Houston, 1983 Office: 206 ChE Building Telephone: 225.578.3058 E-mail: hjortso@lsu.edu

My research interests are in the general area of kinetics/dynamics of biological systems. Past work has primarily been in the areas of cell adhesion, plant tissue culture and population balance models, the latter with a focus on models of budding yeast.

• Cell Adhesion
  
  
• Plant Tissue Culture
  
  
• Population Balance Models
  
  

Cell Adhesion

I first became interested in cell adhesion as a tool for process control of mixed cultures. The idea was, that by taking a process stream from the bioreactor, passing it through a cell affinity chromatographic column to separate the two strains and recycling the slower growing strain to the reactor, it would be possible to stabilize an otherwise unstable mixed culture. We developed models of both the process itself and of specific cell adhesion and did experiments to evaluate the effectiveness of the cell affinity chromatographic columns as well as experiments on a mixed culture, experiments that demonstrated the feasibility of the idea. The experiments were done with two strains of Escherichia coli that differed in expression of the LamB receptor and the strains were successfully separated on an immobilized starch column.

Some relevant publications:

J.W. Roos and M.A. Hjortso (1989), Control of Mixed Microbial Cultures via Specific Cell Adhesion. Biotechnology and Bioengineering 33, 638-649.

J.W. Roos and M.A. Hjortso (1989), Determination of Population Balances in a Mixed Culture by Specific Cell Adhesion. Biotechnology Techniques 3, 7-12.

J.W. Roos and M.A., Hjortso (1991), Control of an Escherichia coli Mixed Culture via Affinity Binding. Biotechnology and Bioengineering 38, 380-388.

J.W. Roos and M.A. Hjortso, (1993) A Mathematical Model of Specific Cell Adhesion: Release of Specifically Adhering Populations by Soluble Ligands, Biofouling 6, 381-404.

J.W. Roos and M.A. Hjortso, eds.,Cell Adhesion : Fundamentals and Biotechnological Applications, Marcel Dekker 1995.

Plant Tissue Culture

Plant tissue cultures are studied primarily because higher plants produce a wealth of valuable secondary metabolites, such as pharmaceuticals, agrichemicals, flavors and fragrances. It is a common hope that these compounds can one day be produced in tissue cultures, rather than from field grown plants, in order to avoid problems and restrictions caused by climatic limitations, seasonal cycles, plant diseases etc.

Plant cell culture was for many years the preferred system to work with but it was found that plant secondary metabolites are typically only produced in significant amounts when the cells differentiate to form the organ that is characteristic of the metabolite. This suggests the use of plant organ culture. However, organ culture is problematic because growth rates in organ cultures are very low, and doubling times may be of the order of months. We chose to work with cultures of transformed roots or hairy roots. These are roots that have been genetically transformed by infection with the soil bacterium Agrobacterium rhizogenes. The transformation results in roots with a profusion of root hairs, thus the name ``hairy roots'', and growth rates far exceed those of untransformed roots.

As part of the project we established a large number of hairy root clones. We investigated growth and secondary metabolite production in these cultures and the ability of fungal and abiotic elicitation to enhance the production of plant secondary metabolites. We developed population balance models of root growth and explored several designs for hairy root reactors, including a flow cell reactor that allowed us to study the growth of a single tip as it elongated and branched. In collaboration with Dr. Klaus Fischer in the LSU Chemistry Department, we used the larger ``production reactors'' we developed to carry out biosynthetic studies in hairy roots with ¹³C-labeled precursors. The high growth rates and high amounts of secondary metabolites produced, combined with the large amounts of root mass we could produce in the reactors, made our setup ideal for these studies.

Some relevant publications:

U. Mukundan and M.A. Hjortso (1990), Effect of Fungal Elicitors on Thiophene Production in Hairy Root Cultures of Tagetes patula. Applied Microbiology and Biotechnology 33, 145-147.

U. Mukundan and M.A. Hjortso (1990), Thiophene accumulation in hairy roots of Tagetes patula in response to fungal elicitors. Biotechnology Letters 12, 609-614.

U. Mukundan and M.A. Hjortso (1990), Thiophene Content in Normal and Transformed Root Cultures of Tagetes erecta: A Comparison with Thiophene Content in Roots of Intact Plants. Journal of Experimental Botany 41, 1497-1501.

U. Mukundan and M.A. Hjortso (1991), Growth and thiophene accumulation by hairy root cultures of Tagetes patula in media of varying initial pH. Plant Cell Reports 9, 627-630.

M.A. Menelaou, D. Vargas, N.H. Fischer, M. Foroozesh, T.M. Thibodeaux, M.A. Hjortso and A.F. Morrison (1991), Biosynthetic Studies of Bithiophenes in Hairy Root Cultures of Tagetes patula using ¹³C-labeled Acetates. Spectroscopy Letters 24, 353-370.

U. Mukundan and M.A. Hjortso (1991), Effect of Light on Growth and Thiophene Accumulation in Transformed Roots of Tagetes patula. Journal of Plant Physiology 138, 252-255.

M.A. Menelaou, F.R. Fronczek, M.A. Hjortso, A.F. Morrison, M. Foroozesh, T.M. Thibodeaux, H.E. Flores and N.H. Fischer (1991), NMR Spectral Data of Benzofuranes and Bithiophenes from Hairy Root Cultures of Tagetes patula. Spectroscopy Letters 24, 1405-1413.

M.D. Gomez-Barrios, F. Parodi, D. Vargas, L. Quijano, M.A. Hjortso, H.E. Flores and N.H. Fischer, (1992), Studies on the Biosynthesis of Thiarubrine A in Hairy Root Cultures of Ambrosia artemisiifolia Using ¹³C-Labeled Acetates, Phytochemistry 31, 2703-2707.

J. Flint-Wändel and M.A. Hjortso, (1993), A flow cell reactor for the study of growth kinetics of single hairy roots, Biotechnology Techniques 7, 447-452.

T. Lu, F.J. Parodi, D. Vargas, L. Quijano, E.R. Mertooetomo, M.A. Hjortso and N.H. Fischer, (1993) Sesquiterpenes and tiarubrines from Ambrosia trifida and its transformed roots, Phytochemistry 33, 113-116.

S. Kim, E. Hopper and M.A. Hjortso, (1995) Hairy Root Growth Models: The Effect of Different Branching Patterns, Biotechnology Progress 11, 178-186.

Q. Song, M.L. Gomez-Barrios, E.L. Hopper, M.A. Hjortso and N.H. Fischer, (1995), Biosynthetic studies of lactucin derivatives in hairy root cultures of Lactuca floridana using ¹³C-labeled precursors. Phytochemistry 40, 1659-1665.

Won Sik Shin and M. A. Hjortsø, (1998), A Tissue Embedding Technique for

Measuring the Structure of Hairy Root Mats of Tagetes erecta. Korean Journal of Chemical Engineering 15, 150-156.

M.A. Hjortso, Mathematical Modeling of hairy Root Growth. In: Hairy Roots, 169-178, Ed. P. Doran, Hardwood Academic Publishers, 1997.

Population Balance Models

I started working with population balance models for my Ph.D. project and have maintained an interest in these models ever since. My Ph.D. project involved modeling of the distribution of states in yeast cultures, and I developed new solution methods for these models.

Since then, I have used population balance models to describe root growth and I have shown that induction synchrony, the phenomena that cells will synchronize their divisions when subjected to certain periodic changes in the environment, has a very natural explanation in terms of the dynamic properties of population balances. During a sabbatical at The Technical University of Denmark in 1992-93, I worked with Dr. Jens Nielsen to extend this idea to autonomous oscillating yeast cultures and we showed that population balances, when coupled to a substrate balance, possess periodic solutions that can explain the observed spontaneous oscillations in continuous yeast cultures.

I think the most important finding in our experimental, work with oscillating yeast cultures was that the state of continuous cultures of Saccharomyces cerevisiae, at a given operating point, is not unique but depends in a complex way on how the operating point is approached: At some operating points, continuous cultures may either be in a steady state or in one of two possible oscillatory states. We also developed population balance models of these cultures that reflect some of these dynamic phenomena.

Some relevant publications:

M.A. Hjortso (1987), Periodic Forcing of Microbial Cultures. A Model for Induction Synchrony. Biotechnology and Bioengineering 30, 825-835.

M.A. Hjortso and J. Nielsen, (1994) A conceptual model of autonomous oscillations in microbial cultures, Chemical Engineering Science 49, 1083-1095.

M.A. Hjortso, (1995), Solution and properties of age population balance models which assume discrete division ages, Journal of Biotechnology 42, 255-269.

M.A. Hjortso and J. Nielsen, (1995), Population balance models of autonomous microbial oscillations, Journal of Biotechnology 42, 271-280.

M. A. Hjortso, (1996), Population balance models of autonomous periodic dynamics in microbial cultures, Canadian Journal of Chemical Engineering 74, 612-620.

Michael J. Kurtz, Guang-Yan Zhu, Abdelqader Zamamiri, Michael A. Henson, and Martin A. Hjortsø, (1998), Control of Oscillating Microbial Cultures Described by Population Balance Models, IEC Research 37, 4059-4070.

M.J. Kurtz, M.A. Henson and M.A. Hjortsø, (2000), Nonlinear Control of Competitive Mixed-Culture Bioreactors via Specific Cell Adhesion, Canadian Journal of Chemical Engineering 78, 237-247.

G. Birol, A. M. Zamamiri and Martin A. Hjortsø, (2000), Frequency analysis of autonomously oscillating yeast cultures, Process Biochemistry 35, 1085-1091.

G.Y. Zhu. A. Zamamiri, M.A. Henson and M.A. Hjortsø, (2000), Model Predictive Control of Continuous Yeast Bioreactors Using Cell Population Balance Models, Chemical Engineering Science 55, 6155-6167.

Abdel-Qader M. Zamamiri, Gülnur Birol and Martin A. Hjortsø, (2001), Multiple Stable States and Hysteresis in Continuous, Oscillating Cultures of Budding Yeast, Biotechnology and Bioengineering 75, 305-312.

Abdelqader M. Zamamiri, Yongchun Zhang, Michael A. Henson and Martin A. Hjortsø, (2002), Dynamics Analysis of an Age Distribution Model of Oscillating Yeast Cultures, Chemical Engineering Science 57, 2169-2181.

Yongchun Zhang, Abdelqader M. Zamamiri, Michael A. Henson and Martin A. Hjortsø, (2002), Cell population models for bifurcation analysis and nonlinear control of continuous yeast bioreactors, Journal of Process Control 12, 721-734.

Prashant Mhaskar, Martin A. Hjortsø and Michael A Henson, (2002), Cell Population Modeling and Parameter Estimation for Continuous Cultures of Saccharomyces cerevisiae, Biotechnology Progress 18, 1010-1026

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Last Modified on October 6, 2003