<P> Natural transformation is a bacterial adaptation for DNA transfer that depends on the expression of numerous bacterial genes whose products appear to be responsible for this process . In general, transformation is a complex, energy - requiring developmental process . In order for a bacterium to bind, take up and recombine exogenous DNA into its chromosome, it must become competent, that is, enter a special physiological state . Competence development in Bacillus subtilis requires expression of about 40 genes . The DNA integrated into the host chromosome is usually (but with rare exceptions) derived from another bacterium of the same species, and is thus homologous to the resident chromosome . </P> <P> In B. subtilis the length of the transferred DNA is greater than 1271 kb (more than 1 million bases). The length transferred is likely double stranded DNA and is often more than a third of the total chromosome length of 4215 kb . It appears that about 7 - 9% of the recipient cells take up an entire chromosome . </P> <P> The capacity for natural transformation appears to occur in a number of prokaryotes, and thus far 67 prokaryotic species (in seven different phyla) are known to undergo this process . </P> <P> Competence for transformation is typically induced by high cell density and / or nutritional limitation, conditions associated with the stationary phase of bacterial growth . Transformation in Haemophilus influenzae occurs most efficiently at the end of exponential growth as bacterial growth approaches stationary phase . Transformation in Streptococcus mutans, as well as in many other streptococci, occurs at high cell density and is associated with biofilm formation . Competence in B. subtilis is induced toward the end of logarithmic growth, especially under conditions of amino acid limitation . </P>

Cells that can be transformed are said to be