Bacteria, genetic engineering with

A new approach to study root exudation of distinct compounds in soil-grown plants uses inoculation of roots with genetically engineered reporter bacteria, which are able to indicate the presence of particular compounds by indicator reactions, such as production of ice-nucleation proteins. This technique has been employed to detect the release of amino acids from roots of soil-grown A vena harbata (56). 

The polymerase chain reaction (PCR) is an important procedure in genetic engineering that allows any DNA segment to be replicated (amplified) without the need for restriction enzymes, vectors, or host cells (see p. 258). However, the nucleotide sequence of the segment has to be known. Two oligonucleotides (primers) are needed, which each hybridize with one of the strands at each end of the DNA segment to be amplified also needed are sufficient quantities of the four deoxyribonucleo-side triphosphates and a special heat-tolerant DNA polymerase. The primers are produced by chemical synthesis, and the polymerase is obtained from thermostable bacteria. 

Panel (a) shows 8 test strips impregnated with genetically engineered E. coli bacteria whose genes are turned on by arsenite (HAsO ). When the strips are exposed to drinking water, a blue spot develops whose size increases with the concentration of arsenite in the water. By comparing the spot with a set of standards, we can estimate whether arsenic is above or below 50 ppb. We call the test strip a biosensor, because it uses biological components in its operation. 

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