Ammonium limitation

The polymerase can occur in either a soluble (hydrophilic) or a granule-bound (hydrophobic) form, depending on prevailing conditions of life. During growth under carbon substrate limitation, the enzyme exists mainly in the soluble state, and after transfer to nutrient-limiting conditions, e.g., ammonium limitation, the granule-associated polymerase appears (for review see [25]). 

However, in practice, qp often declines some time after reaching the maximum value. It has been repeatedly reported that under conditions of ammonium-limited poly(3HB) accumulation, a small amount of ammonium feeding can prolong periods of constant qp values, or even increase maximum values... 

Rhodobacter capsulatus B10 Chemostat wih ammonium limitation, lactate, continuous argon flow (100 ml/min), light saturation 88 0.115 97 Tsygankov et al., 1998... 

A. A. Tsygankov, T. Laurinavichene, I. Gogotov, Y. Asada, J. Miyake (1996) Switching over from light limitation to ammonium limitation of chemostat cultures of Rhodobacter capsulatus grown in different types of photobioreactors. J. Marine Biotechnol., 4 43-46... 

Conway, H. L., Harrison, P. J., and Davis, C. O. (1976). Marine diatoms grown in chemostats trader silicate or ammonium limitation. 11. Transient response of Skeletonema costatum to a single addition of the limiting nutrient. Mar. Biol. 35, 187—199. 

At any biomass concentration the culture was ammonium-limited (data not shown). The increase in incident light intensity (Table 2) affected neither the hydrogen production by the photobioreactor nor the specific activity of the cells. Thus, the culture was not limited by light even at high biomass concentrations. Measurements of residual lactate concentration showed that only at the highest biomass content it was quite low (100 pM), possibly limiting the culture. 

THE SPECIFIC RATE OF HYDROGEN EVOLUTION AND THE VOLUMETRIC RATE OF HYDROGEN EVOLUTION BY AMMONIUM-LIMITED CHEMOSTATCULTURE OF RB. CAPSULATUS AS A FUNCTION OF BIOMASS CONCENTRATION (TSYGANKOV ET AL., 1998)... 

Harrison, P.J., Conway, H.L. and Dugdale, R.C. (1976) Marine diatoms grown in chemostats under silicate or ammonium limitation. I. Cellular chemical composition and steady-state growth kinetics of Skeletonema costatum. Marine Biology, 35, 177-186. 

Figure 4. Variation of cell volume with growth rate. For glucose-limited cells O, data from Cornell , data from Ref. 64. For ammonium-limited cells A. data from Cornell. Solid line, the model s prediction for glucose-limited cells dashed line, models prediction for ammonium-limited cells.

Burkholderia cepacia (formerly Pseudomonas cepacia), a Gram-negative bacterium, is able to utilize a wide variety of carbon sources and accumulate PHAs under nutrient-limiting conditions and excess carbon (Young et al. 1994 Ramsay et al. 1995). Ramsay et al. (1995) have shown its ability to utilize xylose on an ammonium-limited medium and produce P(3HB). Batch fermentation data showed that when xylose was the single substrate, the maximum specific P(3HB) production rate, the yield of P(3HB) produced from substrate consumed (Yphb/s). and the percentage of P(3HB) accumulated in the cells were 0.072 g/(g h), 0.11 g g and 45 % (w/w), respectively. These results were very similar to the ones published for this strain on fmctose. 

Below figure 2 shows distinct granules of PHB in a cell of Alcaligenes latus DSM 1122, growing under ammonium limiting conditions. 

Figure 2 Alcaligenes latus DSM 1122, growth under ammonium limiting conditions A Cell in the Late Accumulation Phase showing distinct granules of PHB. The PHB content is about 93% of cell dry weight.

Ammonium limit test (31) Oxygen flask combustion method... 

In comparison with oxygen, ammonium is absolutely required for growth if no other nitrogen source is available. In fact it is a non-substitutable nutrient for biosynthesis whereas oxygen is an electron acceptor that can be substituted by glucose (reduced to ethanol). If glucose conversion is not complete due to ammonium limitation, the restriction of ammonium supply compared to glucose uptake is expressed as ... 

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