Exopolysaccharide production

In this section we will consider the energetics of exopolysaccharide production in some detail. We will see how chemostat (substrate limited) derived yield coefficients and slfbstrate elemental balances can be used to determine how the nature of the substrate influences... 

The energetic requirements of exopolysaccharide production from various carbon sources can be calculated if the P/O quotient during growth on the carbon substrate is known. Table 3.1 shows molar growth yields measured during carbon limited growth in chemostat culture. 

We can see from Table 3.1 that the P/ O quotient is virtually independent of the carbon constant P/O source. We can therefore assume a constant P/O quotient when calculating the, , olient energetic consequences of exopolysaccharide production from different carbon sources. 

Table 3.1 Parameters of growth and exopolysaccharide production for Agrobacterium radiobacter grown in chemostat culture on various carbon sources. Data obtained from Linton J. D. et al (1987) Journal of General Microbiology 133, 2979-2987.

Examine Table 3.1. What is the relationship between specific rate of exopolysaccharide production and growth efficiency ... 

In order to quantify the scope for improvement of exopolysaccharide production, it is first necessary to correct the observed yields of exopolysaccharide for the amount of carbon substrate and oxygen required for cell production. The corrected yields are then compared with the theoretical calculated from the P/O quotient for the producing micro-organism. Such a comparison is made in Table 3.3. 

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

The requirement for oxygen and carbon source for cell biosynthesis are calculated using nitrogen-limited mass balance equations for growth during exopolysaccharide production 01 res (nitrogen-limited cultures). These balances are derived from experimentally determined values of ... 

Experimentally determined yields of exopolysaccharide have been found to be 70% of the theoretical. This suggests that exopolysaccharide production is an efficient process with little scope for major yield improvements. 

Media used for laboratory studies of exopolysaccharide production may vary considerably from industrial production media. In laboratory studies pure substrates such as glucose, sucrose and glycerol, can be used to determine exopolysaccharide yields. In industrial production the main factors that influence the decision as to which substrate to use are ... 

The medium used to produce the inoculum should be designed for rapid growth of the production organism without exopolysaccharide production. Production of the latter in the inoculum train can give rise to highly viscous cultures that are difficult to transfer from one vessel to another. 

In the sucdnoglycan fermentation, exopolysaccharide production commences after cessation of growth. During the 80 hour production phase of the fermentation, there is a linear increase in product concentration and a linear decrease in residual glucose. 

The specific rate of exopolysaccharide production (qp) is inversely related to growth efficiency (Yq ). 

Glucose source of carbon and energy for growth and exopolysaccharide production. 

M. Korakli, A. Rossmann, M. G. Ganzle, and R. F. Vogel, Sucrose metabolism and exopolysaccharide production in wheat and rye sourdoughs by Lactobacillus sanfranciscensis, J. Agric. Food Chem., 49 (2001) 5194-5200. 

Davies, D. G., A. M. Chakrabarty, and G. G. Geesey. 1993. Exopolysaccharide production in biofilms substratum activation of alginate gene expression by Pseudomonas aeruginosa. Applied and Environmental Microbiology 59 1181-1186. 

Macromolecules such as exopolysaccharides and humic condensates affect the distribution of microorganisms and nutrients within the water column by adding microstructure. Many planktonic bacteria and algae secrete polysaccharides. In some circumstances, exopolysaccharide production is a substantial portion of gross production. The adaptive significance of this activity is unclear. Possibilities include the dumping of excess photosynthate,... 

In this section we will consider the energetics of exopolysaccharide production in some detail. We will see how chemostat (substrate limited) derived yield coefficients and elemental balances can be used to determine how the nature of the substrate influences rates of metabolite production, and to give an indication of the scc for improvement of the producing micro-organism. You should note that for most industrial bioprocesses, the unavailability of data in the primary literature would prevent such an andysis. Further aspects of exopolysaccharide production are covered in Chapter 7 of flus text. 

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