Stoichiometry cell growth

Table 3.3 Experimental stoichiometries for cell growth and exopolysaccharide production from various carbon sources by Agrvbacterhim radlobacter under nitrogen-limiting conditions.

The indirect methods for measuring cell mass are based on the overall stoichiometry for growth and product formation, which may be written in the general form ... 

Since many biochemical reactions and their stoichiometry are not well understood, we often find a more empirical approach to the quantitative assessment of the kinetics. Mass concentration units (e.g., g/L) are often used along with yield coefficients to calculate the distribution of products formed and the amount of substrate consumed. In the absence of any inhibition effects and in the presence of an infinite supply of substrate, the rate of cell growth rx is autocatalytic, that is, it depends only on the concentration of cells (Cx), and the more cells we have, the higher the growth rate. The cell biomass is typically represented by X ... 

The stoichiometry for cell growth is very complex and varies with micra-organism/nutrient system and environmental conditions such as pH, temperature, and redox potential. This complexity is especially true when more than one nutrient contributes to cell growth, as is usually the case. We shall focus our discussion on a simplified version for cell growth, one that is limited by only one nutrient in the medium. In general, we have... 

Assuming that a single nutrient is limiting, cell growth is the only process contributing to substrate utilization, and that cell maintenance can be neglected, the stoichiometry is... 

Naus J, Melis A. (1991). Changes of photosystem stoichiometry during cell growth in Dunaliella salina cultures. Plant Cell Physiol. 32, 569-575. 

If a single nutrient is limiting, and it is only used for cell growth, cell mass and substrate concentrations, Cc and Cs, can be related through the stoichiometry, to lead to... 

Now lets consider the elemental approach to stoichiometry for a relatively simple situation aerobic growth where the only products formed are cells, carbon dioxide and water. The following formulas can be used if we consider the four main elements ... 

Na+,H+ antiporters (NHE) occur in synaptosomes, glia and neuroblastoma cells [60] (Fig. 5-8B). They are relatively inactive at neutral pH but with a decrease in intracellular pH they produce an efflux of protons at the expense of the Na+ gradient. The NHE transport stoichiometry is 1 1. Activation by an internal pH decrement apparently results from protonation of a cytoplasmic site, which allosterically increases the affinity of the proton ionophoric site. In some cells, the NHE is under additional control by receptor mechanisms. Several growth factors and hormones produce transient cytoplasmic alkalinization, probably by mediating a protein kinase... 

Feeding and growth rates, egg production and hatching success, and fecal pellet production are affected by both quantity and quality of food supply (Abou Debs, 1984 Besiktepe and Dam, 2002 Frost, 1972 Tang and Taal, 2005). Changes in food quality can create a mismatch in stoichiometry between predator and prey (Sterner and Hessen, 1994) and effect all of the above parameters, as well as body N content, and ultimately zooplankton production and biomass. In fact the nutritional status of phytoplankton (N cell quotas), not the phytoplankton biomass, may be the major bottom-up determinant of zooplankton biomass (Hessen, 1992 Sterner and Hessen, 1994) except in periods of low food availability (Jonasdottir et al., 2002). 

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