When calculating cell-growth thermodynamics, reconsider using the Gibbs free energy equation

Jun 10, 2013

A forthcoming article in The Quarterly Review of Biology provides the basis for an argument against using the Gibbs free energy equation to accurately determine the thermodynamics of microbial growth.

Microbial growth is a that has been previously treated as a chemical reaction operating in accord with the Gibbs equation, developed during the 1870s. The heat of yeast growth was the first to be measured by direct calorimetry, in 1856.

However, the full application of the Gibbs equation to microbial growth did not occur until 1997, with the experimental measurement of yeast cell entropy. Subsequent investigations showed that the quantity of absorbed for solid substances had two values, depending on how it was calculated. Because there can be only one correct value at a given temperature, Dr. Edwin H. Battley, emeritus of Stony Brook University and recipient of the International Society for Biological Calorimetry's Dubrunfaut Award (1994) and Lavoisier Medal (2010), examined the use of the Gibbs free energy equation to accurately determine the change in energy that accompanies cellular growth.

In many systems, the values for some variables cannot be determined experimentally and so must be calculated from theoretically derived values. The free energy change accompanying cellular growth cannot be directly measured but, if the heat of growth can be measured and the entropy change accompanying growth can be calculated indirectly from heat measurements, the free energy change can be calculated using the Gibbs free energy equation.

The basis for Battley's review is in the observation of an apparent discrepancy between the amounts of growth obtained when S. cerevisiae was grown on glucose in aerobic or . Assuming it is the change in the Gibbs energy that drives the reactions that occur in both conditions, it is expected that the amount of growth would be proportional to the amount of nonthermal energy initially available and there would be 13.2 times more growth aerobically than anaerobically. However, when the growth for these two systems was measured turbidometrically, this value was found to be only 3.4. It is clear that a discrepancy exists between what is theoretically expected and what is experimentally determined.

Using results of earlier studies, Battley devised a different equation to calculate the thermodynamics of microbial growth. This involves using a different mathematical procedure to calculate enthalpy values for absorbed thermal energy exchange. As a consequence, values for entropy used for this purpose are removed. He found that the application of this equation (which he calls the Battley free energy equation) achieved values different from those obtained using the Gibbs free energy equation for the same system. Because the Battley free energy equation uses an absorbed thermal energy variable that is easier to understand in the context of the real-world system in which microbes exist, Battley argues that his free energy equation more realistically represents real-world conditions, and in a way that is more simple and parsimonious to calculate. As such, it is superior for determining the thermodynamics of microbial growth than is the Gibbs free energy equation.

Explore further: Microbes provide insights into evolution of human language

More information: Battley, Edwin H. "A Theoretical Study of the Thermodynamics of Microbial Growth Using Saccharomyces cerevisiae and a Different Free Energy Equation." Quarterly Review of Biology Vol. 88, No. 2 (June 2013).

add to favorites email to friend print save as pdf

Related Stories

New equation of state of seawater

Feb 05, 2009

Seawater is a complex, dynamic mixture of dissolved minerals, salts, and organic materials that despite scientists best efforts, presents difficulties in measuring its potential to contain and disperse energy. Like the water ...

Evaluating the energy balance of Saturn's moon Titan

Jan 02, 2012

To understand the weather and climate on Earth as well as on other planets and their moons, scientists need to know the global energy balance, the balance between energy coming in from solar radiation and thermal energy radiated ...

Recommended for you

Cell division speed influences gene architecture

19 hours ago

Speed-reading is a technique used to read quickly. It involves visual searching for clues to meaning and skipping non-essential words and/ or sentences. Similarly to humans, biological systems are sometimes ...

Secret life of cells revealed with new technique

21 hours ago

(Phys.org) —A new technique that allows researchers to conduct experiments more rapidly and accurately is giving insights into the workings of proteins important in heart and muscle diseases.

In the 'slime jungle' height matters

21 hours ago

(Phys.org) —In communities of microbes, akin to 'slime jungles', cells evolve not just to grow faster than their rivals but also to push themselves to the surface of colonies where they gain the best access ...

Queuing theory helps physicist understand protein recycling

Apr 22, 2014

We've all waited in line and most of us have gotten stuck in a check-out line longer than we would like. For Will Mather, assistant professor of physics and an instructor with the College of Science's Integrated Science Curriculum, ...

User comments : 0

More news stories

FDA proposes first regulations for e-cigarettes

The federal government wants to prohibit sales of electronic cigarettes to minors and require approval for new products and health warning labels under regulations being proposed by the Food and Drug Administration.

Brazil enacts Internet 'Bill of Rights'

Brazil's president signed into law on Wednesday a "Bill of Rights" for the digital age that aims to protect online privacy and promote the Internet as a public utility by barring telecommunications companies ...