(i) Some useful strains of Agrobacterium tumefaciens (known to cause crown gall diseases) are:
(a) Agrobacterium radiabacter K84 is useful for biological control.
(b) Agrobacterium sp. M4 is a source of an experimental drug for cholesterol degradation.
(c) Agrobacterium radiobacter J14 helps in biodegradation of Atrazine, an agricultural herbicide.
(ii) Erwinia amylovora is a causative organism of fire blight disease but also serves as an elicitor of disease resistance in plants.
(iii) Xanthomonas campestris a causative organism of black rot, is also a source of xanthum gum. It is a polysaccharide used in agriculture, cosmetics and pharmaceuticals.

Application These bioreactors are used to produce large quantities of products enzymes, etc., using microbial, plant, animal of human cells.

Since, DNA is a hydrophilic molecule, it cannot pass through the cell membranes. In order to force bacteria to take up the plasmid, the bacterial cells must first be made competent to take up DNA. This is done by treating them with a specific concentration of a divalent cation such as calcium, which increases the efficiency with which DNA enters the bacterium through the pores in its cell wall.
Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42 C (heat shock) , and then putting them back on ice. This enable the bacteria to take up the recombinant DNA.

(i) A - Denaturation process
(ii) B - Primers
(iii) C - Taq DNA polymerase. Taq polymerase is a thermostable enzyme, which remains active during the high temperature and incduces denaturation of DNA