Diauxic growth

Microorganisms exhibit nutritional preferences. The enzymes for common substrates such as glucose are usually constitutive, as are the enzymes for common or essential metabohc pathways. Furthermore, the synthesis of enzymes for attack on less common substrates such as lactose is repressed by the presence of appreciable amounts of common substrates or metabolites. This is logical for cells to consei ve their resources for enzyme synthesis as long as their usual substrates are readily available. If presented with mixed substrates, those that are in the main metabolic pathways are consumed first, while the other substrates are consumed later after the common substrates are depleted. This results in diauxic behavior. A diauxic growth cui ve exhibits an intermediate growth plateau while the enzymes needed for the uncommon substrates are synthesized (see Fig. 24-2). There may also be preferences for the less common substrates such that a mixture shows a sequence of each being exhausted before the start of metabolism of the next. 

Diauxic growth. Growth on a mixture of two carbon sources in which one carbon source is used up before the other one is mobilized. For example, in the presence of glucose and lactose,... 

The fourth criterion of mutual immiscibility of the diluent and the feed phase is important for several reasons. The lower the diluent solubility in the treated wastewater, the less likely it is that diauxic growth or co-metabolism wiU occur [34]. The lower the solubility of the diluent in the feed phase, the higher the recovery of the diluent at the end of the treatment of one batch of the feed phase, that is, wastewater. This reduces losses of the diluent used, thus treatment costs are lower due to decreased costs of solvent procurement. 

A classic example in which the internal regulatory processes of the cells play a very important role is the phenomenon of diauxic growth discovered by Monod [ 9 ] in multiple substrate systems. In diauxic growth there is preferential utilization of certain substrates over others, although each substrate by Itself... 

In what follows we will present two models, one based on a long term perspective and another based on a short term perspective both addressing the phenomenon of diauxic growth in multiple substrate systems. 

Figure I. The diauxic growth curve predicted by Dhurjati s model for Klebsiella pneumoniae grown on a glucose-xylose mixture. Dashed lines, model solid line,...

Figure 3. The diauxic growth curve predicted by Kampala s short term model. AG (glucose) = 90.0 AX (xylose) = 60.0.

Model of the Lac Operom Inducer Exclusion, Catabolite Repression, and Diauxic Growth on Glucose and Lactose. 

Catabolite repression plays a central role in many industrial fermentations such as in yeast technology (diauxic growth) and secondary metabolite productions. Even though the exact nature of the biochemical mechanisms involved in these regulations is often unknown (see Demain et al., 1979), the following type of formal kinetic equation... 

Figure 5.48. Multisubstrate kinetics for a two-substrate reaction (a) Concentration/ time diagram for strictly sequential substrate utilization (diauxic growth), (b) Partly overlapping and partly sequential substrate use. (c) Simultaneous substrate utilization. Sum-type kinetics are often applied in (b) and (c).

Generally, in multicomponent media, substrates will be utilized sequentially. Physiologically, two different responses can be distinguished, known as cata-bolite repression and inhibition, both resulting in a diauxic growth pattern. Remarkable differences in growth behavior can be observed comparing batch and continuous operation in a CSTR (Harder and Dijkhuizen, 1975), due to the existence of much lower steady-state concentrations of Sj in CSTRs so that the effects of both repression and inhibition may be absent or reduced. 

The S. cerevisae cells can metabolise glucose via two pathways under aerobic conditions oxidative and/or reductively, with ethanol being the end product of the reductive pathway. The cells are able to use ethanol as a second substrate (the phenomenon of diauxic growth), but ethanol can be metabolised oxidative only. The 3 metabolic pathways may be stated by the following macroscopic reactions ... 

Loose C, Jensen K, Rigoutsos I, Stephanopoulos G (2006) A linguistic model for the rational design of antimicrobial peptides. Nature 443 867-869 Mahadevan R, Edwards JS, Doyle FJ 3rd (2002) Dynamic flux balance analysis of diauxic growth... 

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