Bacteria auxotrophic

Nucleotide Biosynthesis in Amino Acid Auxotrophic Bacteria Normal E. coli cells can synthesize all 20 common amino acids, but some mutants, called amino acid aux-otrophs, are unable to synthesize a specific amino acid and require its addition to the culture medium for optimal growth. Besides their role in protein synthesis, some amino acids are also precursors for other nitrogenous cell products. Consider the three amino acid auxotrophs that are unable to synthesize glycine, glutamine, and aspartate, respectively. For each mutant, what nitrogenous products other than proteins would the cell fail to synthesize ... 

Ames test Test used to determine whether a particular substance is mutagenic, based on its ability to induce mutations in auxotrophic bacteria. A strain of the bacterium Salmonella typhimurium having a mutation that disables an enzyme necessary for histidine utilization is exposed to the substance in question and plated on a medium lacking histidine. A reversion mutation that activates the mutant enzyme causes the cells to grow on this medium. 

Tumor-targeting can also be controlled by the creation of auxotrophic bacteria that are not able to survive without nutrients from specific microenvironments and apparently they only receive sufficient nutritional support from tumors (Zhao et al., 2005, 2006, 2007 Hayashi et al., 2009). 

The introduction of techniques for mutagenesis by UV irradiation or by the use of chemicals considerably extended the applications of microbial studies to nutrition (Davis, 1954-1955). Auxotrophic mutants were produced with nutrient dependencies not shown in the untreated parental strains (Beadle and Tatum, 1940). The fortuitous discovery of penicillin by Fleming and its successful use in the treatment of infections (Florey) promoted exhaustive research into its mode of action. Eventually it was established that penicillin prevented the proliferation of gram-positive bacteria by blocking the synthesis of their cell walls... 

A certain bacteria that was a tryptophan auxotroph was observed to grow well when it was supplied with tryptophan, but as soon as the tryptophan in the environment was exhausted it started to excrete a metabolite on the tryptophan biosynthetic pathway. Why didn t it excrete the metabolite before it exhausted the environmental tryptophan ... 

The use of genetic mutants determined the complex pathways that lead to the amino acids. A mutant is an organism that has a different DNA sequence from its parent(s). Mutant bacteria that require a specific compound for growth are called auxotrophs. The first step in pathway determination is to assemble a large collection of auxotrophic mutants that can t make the compound of interest. 

With the introduction of radiochemical methods, DNA biosynthesis and its inhibition is usually followed either by measuring the incorporation of radioactive thymine into thymine auxotrophs of bacteria or the incorporation of radioactive thymidine into prototrophic organisms. In the latter instance, it is practical to include in the experimental medium a large excess of non-radioactive deoxyadenosine in order... 

An alternative method has been developed by Tirrell et al. [94-96] and involves the substitution of a natural amino acid with a close structural analogue. This method uses bacterial auxotrophs, which are bacteria that have lost the ability to produce one of the natural amino acids. These bacteria are dependent on the medium for their supply of this amino acid and, therefore, if an analogue is added to the medium it can be incorporated instead. The introduction of azido and acetylene analogues of methionine has also led to the presence of bio-orthogonal functional handles that allow further modification of the proteins. However, this methodology has not yet been extended to the incorporation of synthetic polymers. 

L-Threonine is produced by some auxotrophic mutants and/or threonine-analog resistant mutants and those bred by gene engineering techniques. The bacteria are Escherichia coli, Corynebacterium glutamicum, Brevibacterium lactofermentum, B.flavum, Serratia marcescens, and Proteus retgerii. 

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