Assimilation in Bacteria

This classification is based on whether or not the bacteria take up the Gram stain, devised by Christian Gram in 1884. 

While we tend to talk about transition metals as trace elements, in terms of their actual concentration within individual bacterial cells, they are found at concentrations which are several orders of magnitude higher than the concentration in a typical bacterial growth medium. Thus, in Escherichia coli, Fe and Zn are present at around 2 x 10 atoms/ cell, which corresponds to around 0.1 mM, while intracellular Cu, Mn, Mo, and Se levels are around 10 pM. 

In what follows, we discuss uptake, i.e., assimilation of metal ions from the environment into the organism itself. Later, in Chapter 8, we consider metal transport, storage, and homeostasis within organisms and cells. 

If a bacterial cell waited for simple diffusion of 10 M Fe through porins, it would die instantaneously  

The yeast Saccharomyces cerevisiae goes one better — it itself synthesises no siderophores, but has no less than four plasma membrane facilitators for uptake and internalization of several ferric siderophores. 

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Glutamine synthetase is found in all organisms. In addition to its importance for NHj assimilation in bacteria, it has a central role in amino acid metabolism in mammals, converting toxic free NHj to glutamine for transport in the blood (Chapter 18). 

A schematic representation of glucose and xylose metabolism for PHA production is presented in Fig. 2. The first step for xylose assimilation in bacteria by the PPP is an isomerization to D-xylulose by xylose isomerase, followed by a phosphorylation by xylulokinase that produces D-xylulose 5-phosphate, yielding finally glucose 6-phosphate. This intermediate from the glucose metabolism can be produced by... 

The importance of metal assimilation for bacteria is perhaps best illustrated by the correlation between the efficacy of iron uptake systems and virulence in many strains of pathogenic... 

Lee RW, Robinson JJ, Cavanaugh CM. Pathways of inorganic nitrogen assimilation in chemoautotrophic bacteria-marine in- 63. vertebrate symbioses expression of host and symbiont glutamine synthetase. J. Exp. Biol. 1999 202 289-300. 

An ATP-dependent reduction of pyridine nucleotides (NADH, NADPH) provides the organism with reducing power for CO2 assimilation. In the iron-oxidizing bacteria, this aspect of metabolism has received little attention however, in other thiobacilli, reduction of pyridine nucleotides has been investigated (Aleem, 1970). Since the redox potentials of NAD /NADH and NADP /NADPH are low (Eq = —0.320 and —0.324 V, respectively), and... 

As pointed out in the preceding section, sulfate assimilation in yeast has been shown to involve the activation of sulfate by ATP successively to adenosine 5 -phosphosulfate and once again to 3 -phosphoadenosine 5 -phosphosulfate. The latter is then reduced in the presence of NADPH to sulfite and 3, 5 -diphosphoadenosine (S7 ). Enzymes catalyzing the 6-electron reduction of sulfite to sulfide have been observed in bacteria (339, 38S-397), yeast (398-401), fungi (40S-404), and higher plants (3S9, 405). These enzymes may be divided into two classes depending on... 

Bacteria growing with ammonia as their sole nitrogen source use this reaction as the primary route for nitrogen assimilation. In animal cells, the reversible reaction can function in either direction. The enzyme is allosterically regulated. ATP or GTP inhibits its action. 

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