Limiting nutrient

This is an old, familiar analysis that applies to any continuous culture with a single growth-limiting nutrient that meets the assumptions of perfect mixing and constant volume. The fundamental mass balance equations are used with the Monod equation, which has no time dependency and should be apphed with caution to transient states where there may be a time lag as [L responds to changing S. At steady state, the rates of change become zero, and [L = D. Substituting ... 

FIG. 24-24 Effect of recycle on steady-state concentrations of cell mass and limiting nutrient. 5-fold increase in cell concentration in separator. SiiLscripts denote fraction of cell concentrate recycled. 

Initial carbon-nitrogen ratios (by mass) hetween 35 and 50 are optimum for aerobic composting. At lower ratios ammonia is given off Biological activity is also impeded at lower ratios. At higher ratios nitrogen maybe a limiting nutrient. 

The ehemostat is an arrangement for eontinuous fermentation in whieh the properties of the system are regulated by a eontrolled supply of some limiting nutrient. It is a powerful researeh tool in mierobial physiology and for evaluating proeess parameters. The ehemostat... 

Aim3 aerobic bioprocess was operated in a continuous mode with nitrogen as the growth limiting nutrient. The steady state biomass concentration (x), the biomass yield coefficient (Yx/S) and the product yield coefficient (Yp/t) were determined at a low and at a high dilution rate (D). 

Explain why it would be inadvisable to use the carbon source as growth limiting nutrient in the sucdnoglycan fermentation. 

A shortage of any of some two dozen chemical elements that are essential for the growth of organisms can reduce ecosystem productivity, but phosphorus and nitrogen are often the most limiting nutrients, which is why these two elements are standard components of commercial fertilizers. Phosphorus is often limiting because it moves through soil pores and aquatic... 

Biomass Production. Biomass is usually measured by dry weight of viable cells per unit volume X. We bypass the sometimes tricky problems associated with this measurement except to say that it is the province of the microbiologist and usually involves plate cultures and filtration followed by drying. Suppose there is one limiting nutrient S, and that all other nutrients are available in excess. Then the Monod model for growth is... 

C04-0153. Phosphorus is essential for plant growth, and it is often the limiting nutrient in aqueous ecosystems. 

By necessity, herbivores have evolved GIT and systemic compensatory mechanisms that allow them to subsist on plant-based diets that have limited nutrient quality and include phytochemicals. Still, herbivores remain susceptible to some of the anti-nutrient and toxic phytochemicals. For example, several herbivores are sensitive to the phytotoxins associated with autumn crocus, which include colchicine (Yamada et al, 2000). As a consequence, herbivores tend to select species and portions of plants based on a combination of nutrient quality and concentrations of phytochemicals (Yeager et al, 1997), and this has an impact on habitat selection and plant ecology (Duncan and Gordon, 1999). Carnivorous species have not been under selective pressure to develop similar compensatory mechanisms, generally have only limited abilities to subsist on plant-based diets, and in many cases are less tolerant of phytochemicals. 

Nutrient availability also plays a major role in exudation, with deficiencies in N, P, or K often increasing the rate of exudation (218). It is believed that nutrient deficiency may trigger the release of substances such as organic acids or nonproteinogenic amino acids (phytosiderophores), which may enhance the acquisition of the limiting nutrient (219,220). An example here might be the release of phenolic acids such as caffeic acid in response to iron deficiency, which results in an increase in uptake of the cation (221). 

The morphological and physiological dissimilarities between mycorrhizal symbi-o.ses probably determine their success and their distinct patterns in different ecosystems (92). Nitrogen (N) available to both AM and ectomycorrhizal plants should not be regarded as a single pool open to free competition. Specialization of its acquisition and utilization in a given habitat is an important feature of plant and microbial community structure, while the fact that the ability to exploit its sources (and tho.se of other limited nutrients) is not the same in all species may result in niche differentiation (93). If habitat specialization is a reflection of differences between mycorrhizal types, ectomycorrhizal and AM species could cooccur because they exploit different niches in the. same ecosystem. 

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