Bacterial Genetics :
In bacteria the cells have a single circular strand of DNA. It is not associated with proteins as are eukaryotic chromosomes. The bacterial genes, like the eukaryotic genes possess the features of replication, phenotype expression, mutation and genetic recombination etc. In bacteria the genetic recombination results from three types of gene transfer viz., conjugation, transduction and transformation.
Conjugation involves the transfer of some DNA from one bacterial cell to another followed by the separation of the mating pair of cells. In this, large segments of the chromosomes and in special cases the entire chromosome may be transferred.
Bacterial transformation is a process in which cell free or naked DNA containing the genetic information is transferred from one bacterial cell to another. It was discovered by an English health officer, Griffith in 1928. The transforming principle was identified as DNA by Avery Macleod and Mc Carthy in 1944.
In transduction, a bacteriophages acts as a vector, transfering a por-tion of DNA from one bacterium (donor) to another (recepient). If all frag-ments of bacterial DNA have a chance to enter a transducing phage, the process is called Generalized transduction. On the contrary if a few re-stricted genes of the bacterial chromosomes are transduced by bacterioph-age, it is called specialized transduction.
All bacteria need nutrients for their growth. They need a nutrient medium for their growth and culture. A bacteriological medium is composed of known chemical compounds. It is called a chemically defined medium or synthetic medium, The compounds are carbohydrates, proteins, nucleic acids, lipids, vitamins and other complex organic substances. Certain complex materials include peptones, meat extract, yeast extract etc. The medium with the above raw materials can support the growth of a wide variety of heterotrophic bacteria. Agar is included as a non-nutritive solidifying agent. Nutrient agar and nutrient broth are the simple solid and liquid media for the growth of heterotrophs respectively.