The study investigates the requirements for transformation in Bacillus subtilis strain 168, an indole-dependent strain. It was found that optimal transformation to prototrophy occurs when cells are grown in a glucose minimal medium containing L-tryptophan and acid-hydrolyzed casein. Two growth periods were used: the first 4-hour period, where casein hydrolyzate provided growth stimulation, and the second 90-minute period, where casein hydrolyzate could be replaced by L-histidine or metal chelating compounds. The presence of high concentrations of amino acids, such as those in casein hydrolyzate, reduced transformation sensitivity, likely due to the synthesis of wall components that prevent DNA uptake. A metal ion chelating compound, such as EDTA, was found to be essential for competence, as it complexed cupric ions and enhanced transformation. The optimal time for adding the chelator was during the first half of the 90-minute period, with its presence maintained for about 45 minutes. DNA concentration also affected transformation, with as little as 10^-5 μg/ml of DNA producing transformation, and the response up to 10^-1 μg/ml being linear. The study suggests that some genetic control is involved in the attainment of the competent state, as sensitivity to transformation occurs at a stage of growth when presporulating events occur. Strains unable to undergo sporulation do not become competent. The findings indicate that the development of competence in B. subtilis strain 168 is influenced by specific growth conditions, including the presence of L-tryptophan or indole, and the use of a metal chelating compound. The study also highlights the importance of the cell wall structure and possible enzymatic mechanisms in DNA uptake.The study investigates the requirements for transformation in Bacillus subtilis strain 168, an indole-dependent strain. It was found that optimal transformation to prototrophy occurs when cells are grown in a glucose minimal medium containing L-tryptophan and acid-hydrolyzed casein. Two growth periods were used: the first 4-hour period, where casein hydrolyzate provided growth stimulation, and the second 90-minute period, where casein hydrolyzate could be replaced by L-histidine or metal chelating compounds. The presence of high concentrations of amino acids, such as those in casein hydrolyzate, reduced transformation sensitivity, likely due to the synthesis of wall components that prevent DNA uptake. A metal ion chelating compound, such as EDTA, was found to be essential for competence, as it complexed cupric ions and enhanced transformation. The optimal time for adding the chelator was during the first half of the 90-minute period, with its presence maintained for about 45 minutes. DNA concentration also affected transformation, with as little as 10^-5 μg/ml of DNA producing transformation, and the response up to 10^-1 μg/ml being linear. The study suggests that some genetic control is involved in the attainment of the competent state, as sensitivity to transformation occurs at a stage of growth when presporulating events occur. Strains unable to undergo sporulation do not become competent. The findings indicate that the development of competence in B. subtilis strain 168 is influenced by specific growth conditions, including the presence of L-tryptophan or indole, and the use of a metal chelating compound. The study also highlights the importance of the cell wall structure and possible enzymatic mechanisms in DNA uptake.