RESUMO
Certain species of bacteria can become competent to take up high molecular weight DNA from the surrounding medium. DNA homologous to resident chromosomal DNA is transported, processed and recombined with the resident DNA. There are some variations in steps leading to transformation between Gram-positive bacteria like biplococcus pneumoniae and Gram-negative bacteria represented by Haemophilus influenzae but the integration is by single-strand displacement in both cases. Plasmid (RSF0885) transformation is low in Haemophilus influenzae but this is increased significantly if (homologous) chromosomal DNA is spliced to plasmid DNA. In Haemophilus influenzae, rec1 function is required for peak transformation with chimeric plasmids. Chimeric plasmid fixed presumably extrachromosomally undergoes frequent recombination between homologous segments contained in resident chromosome and the plasmid.