Biomass formation

The destiny of most biological material produced in lakes is the permanent sediment. The question is how often its components can be re-used in new biomass formation before it becomes eventually buried in the deep sediments. Interestingly, much of the flux of phosphorus is held in iron(lll) hydroxide matrices and its re-use depends upon reduction of the metal to the iron(ll) form. The released phosphate is indeed biologically available to the organisms which make contact with it, so the significance attributed to solution events is understandable. It is not clear, however, just how well this phosphorus is used, for it generally remains isolated from the production sites in surface waters. Moreover, subsequent oxidation of the iron causes re-precipitation of the iron(lll) hydroxide floes, simultaneously scavenging much of the free phosphate. Curiously, deep lakes show almost no tendency to recycle phosphorus, whereas shallow... 

Where yield coefficients are constant for a particular cell cultivation system, knowledge of how one variable changes can be used to determine changes in the other. Such stoichiometric relationships can be useful in monitoring fermentations. For example, some product concentrations, such as CO2 leaving an aerobic bioreactor, are often the most convenient to measure in practice and give information on substrate consumption rates, biomass formation rates and product formation rates. 

Biomass formation and transamination activity within the cells develop in a similar manner. Growth usually continues until limited by the availability of dissolved oxygen tension (DOT). After 10-15 hours a dry weight biomass concentration of 10 g V is normally reached. 

Under ideal batch growth conditions, the quantity of biomass, and therefore the biomass concentration will increase exponentially with respect to time and in accordance with all cells having the same probability to multiply. Thus the overall rate of biomass formation is proportional to the biomass itself where... 

The yield (y) of a biomass production process is defined as the moles of biomass formed per mole of substrate consumed. Aerobic conditions are more conducive to higher biomass formation (and therefore also to biofilm formation) than anaerobic conditions. Empirically, under aerobic conditions, a yield of 0.05 - 0.6mol biomass/mol carbon can be obtained, while under anaerobic conditions the attainable yield falls to 0.04 -0.083mol. The reaction kinetics of biodegradation processes can be approximated by the first-order reaction rate constant k as follows ... 

The yield of 1,3-PD for this reaction is 67% (mol/mol). If biomass formation is considered the theoretical maximal yield reduces to 64%. In the actual fermentation a number of other by-products are formed, i. e., ethanol, lactic acid, succinic acid, and 2,3-butanediol, by the enterobacteria Klebsiella pneumoniae, Citrobacter freundii and Enterobacter agglomerans, butyric acid by Clostridium butyricum, and butanol by Clostridium pasteurianum (Fig. 1). All these by-products are associated with a loss in 1,3-PD relative to acetic acid, in particular ethanol and butanol, which do not contribute to the NADH2 pool at all. 

The combined activity of the rubisco oxygenase and the glycolate salvage pathway consumes 02 and produces C02—hence the name photorespiration. This pathway is perhaps better called the oxidative photosynthetic carbon cycle or C2 cycle, names that do not invite comparison with respiration in mitochondria. Unlike mitochondrial respiration, photorespiration does not conserve energy and may actually inhibit net biomass formation as much as 50%. This inefficiency has led to evolutionary adaptations in the carbon-assimilation processes, particularly in plants that have evolved in warm climates. 

Fig. 1. Redox metabolism in Saccharomyces cerevisiae during anaerobic growth on glucose. The ethanol yield is lowered by the production of biomass and glycerol. The glycerol flux, x, can be decreased, and the ethanol yield thereby increased if the stoichiometric coefficient a for biomass formation is reduced, e.g., by having nitrogen assimilation via an NADH-depen-dent glutamate dehydrogenase [10]...

Yurkov V. and Van Gemerden H. (1993) Impact of light/dark regime on growth rate, biomass formation and bacterio-chlorophyU synthesis in Erythromicrobium kydrolyticum. Arch. Microbiol. 159, 84—89. 

This means that, under conditions of catabolite limitation, Eqn. 70 will give the most easily interpretable relation. Conversely, under anabolite limitation, Eqn. 71 will be the most practical. Both equations predict a linear relation between rate of substrate utilization and biomass formation. Furthermore, the relation between catabolism and anabolism has a positive intersection point with the ordinate. This positive catabolism at (extrapolated) zero growth rate has been interpreted as maintenance energy requirement [52]. It follows naturally from the simple description of bacterial metabolism as we have used it here. 

Four microorganisms, delignification, saccharification with Trichoderma sp., biomass formation with Candida utilis and Saccharomyces cerevisiae A.foetidus produces citric acid 16.1 g/ 100 g DM and 3% methanol Amylases... 

Anaerobic biomass formation might be described by the following simplified reaction scheme ... 

However, from the efficiency point of view, it has to be considered that the biomass formation always requires the conversion of solar energy to some type of biomaterial, and this can be realized only by the photosynthesis process, whose energy efficiency is lower than 1% (see Sect. 1.3). 

Plant biomass, formed by photosynthesis from atmospheric CO, is the first organic substrate in the terrestrial carbon cycle (Fig. 1). The net biomass formation rate is estimated as up to... 

R2 represents the cell growth (biomass formation) from glucose with inhibition by lactate. The biomass formed is converted into active cellular material. The reaction rates (i 3) and R4) describe the lactate and acrylic acid formation, respectively. 

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