Nutrient depletion

Thirdly, nutrient depletion and any inhibitory compounds do not, in general, have a large effect on the immobilised cells because the cells are fixed by immobilisation. In batch and CSTR fermentation, nutrient depletion, inhibition and accumulation of toxic by-products are major problems, but immobilised cells are usually unaffected by toxic by-products. 

Several different strategies to overcome nutrient depletion have been used, such as extra nutrient addition to the culture medium prior to infection [68] and partial to complete medium refeeding prior to infection [17]. 

In a closed system the growth rate of a microorganism will ultimately decline to zero. In the absence of other effects this is bound to occur because of nutrient depletion and the... 

The overall life cycle of a particular yeast Saccharomyces (S.) cerevisiae, is summarised in Fig. S.6 which shows how it is possible for the cells to fuse to form various cell and spore types. The figure shows the possible types of reproduction in yeast. Generally, industrial strains of S. cerevisiae, brewers yeast, reproduce by budding/ fission processes and only sporulate under specialised conditions. However, many strains of yeast are capable of cell fusion to form spores or cells with increased genetic complements. Such strains have many sets of chromosomes and are termed polyploid. Active fermentation of industrial strains involves growth by mitotic division and nutrient depletion which results in stationary cells with little or no spore formation. 

Lillo C, Lea US, RuoffP. 2008. Nutrient depletion as a key factor for manipulating gene expression and product formation in different branches of the flavonoid pathway. Plant Cell Environ 31 587-601. 

Bienfang, P. K. and Harrison, P. J., Sinking-rate response of natural assemblages of temperate and subtropical phytoplankton to nutrient depletion, Mar. Biol., 83, 293, 1984. 

Henao, J. and C. Baanante (1999) Nutrient depletion in the agricultural soils of Africa.- 2020 Brief 62, International Monetary Fund, IMF. Washington, D.C., USA. 

Stoorvogel, J.J. and Smaling, E.M.A. (1990) Assessment of soil nutrient depletion in sub-Saharan Africa 1983-2000.- Report 28. Winand Staring Centre, Wageningen, The Netherlands. 

The excess release of DOM under nutrient limitation has not been observed in Phaeocystis. In Phaeocystis sp. cultures DOC production was coupled to POC production at different growth stages (Biddanda and Benner 1997). Also in enclosures of P. antarctica, ratios of recently produced DOC increased only slightly after nutrient depletion (Smith et al. 1998 Carlson et al. 1998). This indicates that nutrient limitation does not lead to increased excretion of DOM resulting from an overflow mechanism. 

Determining the appropriate length of exposure of cells to test compounds can be a balance between the limits of nutrient depletion and the time needed by cells to respond to an experimental treatment. The toxicity of a compound to a population of cells and the magnitude of response can be related to both the concentration and length of exposure (Riss and Moravec 2004). Figures 6.1 and 6.2 show that the duration of exposure of cells to test compounds can directly affect whether the population of cells will be scored as viable, dead or apoptotic. For instance, some test compounds can be exposed for a few hours with no apparent effect on viability, but induce markers of apoptosis. 

As a single-cell organism, a yeast cell is not polar in an organ sense, apical versus basolateral, for example, as is the case of intestinal epithelial cells. As a free-living organism, yeast accumulates nutrients for future use in times of nutrient depletion. Thus, little copper or iron is secreted from the yeast cell. On the other hand, yeast must have a mechanism to mobilize and use stored nutrients. Iron is stored in Sa. cerevisiae in a vesicular compartment, perhaps a (the) vacuole, most likely as an Fe(III) polyphosphate (Raguzzi et al., 1988). This iron phosphate is probably not significandy different... 

Several experiments have examined the role of nutrient depletion in microbial interactions. Mixed -labeled amino acids were added to droplets on sugar beet leaves (wetted 24 hr prior to application) and uptake... 

In the more arid savanna regions of the Amazon basin and Brazilian Cerrado, the problem of nutrient depleted soils is compounded by seasonal water shortages. As discussed by M. Haridasan in chapter 5, savanna vegetation is thus of greatly reduced... 

---