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Chemistry (including Biochemistry)/Stoichiometric balance of mixotrophic growth


Stoichiometric Balance Equations
Stoichiometric Balance  
Dear Trista,
I have been working in a laboratory cultivating microalgae for my Masters Thesis. Part of the thesis requires that I do a stoichiometric mass balance on the mixotrophic growth of algae grown on waste-water. I work mainly with life-cycle analysis and economic modelling, so my experience with biochemistry is a bit limited and am therefor trying to simplify the balance as much as possible. I have been painstakingly combing through the internet for the past month and a half trying to work out how to balance this mixotrophic growth in a way that makes sense. I would be really grateful If you could have a look and tell me if it makes sense or if there is something I am doing wrong. I have included the equations I have balanced as an image in the attachment.

I have combined the heterotrophic and photoautotrophic growth equations into one as I am only interested in the inputs and outputs of the system. The coefficient units are in moles / mole biomass produced. The pH increased from 7.8 -8.1 every 35 minutes and was maintained by CO2 injection. This increase corresponds to an increase in OH- of 38.55 Moles and a decrease in H+ of 0.508 Moles / Mole biomass. As the pH is increasing this would suggest that photoautotrophic activity is greater than heterotrophic. With the pH being around 8 I am assuming that all of the dissolved inorganic carbon being utilized is in the form of HCO3-.
I am having two main Issues with the results of the balance. Firstly, the balance shows a net production of HCO3- and a net consumption of H2O and O2. I would have expected with more photosynthesis than heterotrophy that there would be a net production of O2 and a net consumption of HCO3 and H2O. However the balance doesn’t seem to make sense. If there was more heterotrophic activity I would expect there to be more HCO3 and H2O production where infact more H2O is being consumed. The second issue I am having is that the charges aren’t balancing. The left side has a total charge of -11.824 and the right side has a total charge of -57.879.

Hi Daniel!

WHOA. That's heavy. I have questions.

1) How much of the time does your algae spend fixing light energy?
2) How much of the time does your algae spend eating carbon? What is the biomass they are consuming?

If your microalgae spends more time eating carbon, than production of more CO2 than O2 makes sense, because your algae is burning more carbons than it is fixing. Glycolytic and mitochondrial cellular respiration require O2 and H2O to make ATP.

It may be that you don't want your microalgae to be eating more carbon than fixing it. In this case, you may wish to change the living conditions of the microalgae to favor the light reactions (make sugar from CO2) over the dark reactions (burn sugar to do cellular work).

Good luck with your thesis. In my humble experience, living critters tend to do what they want rather than what you tell them, so ofttimes they must be coaxed or tricked into behaving. :)

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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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