Transformation of Haemophilus influenzae by plasmid RSF0885

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Abstract
Plasmid RSF0885, which conferred ampicillin resistance, transformed competent H. influenzae cells with low efficiency (maximum, < 0.01%). As judged by competition experiments and uptake of radioactivity, plasmid RSF0885 DNA was taken up into competent H. influenza cells several orders of magnitude less efficiently than H. influenzae chromosomal DNA. Plasmid RSF0885 transformed cells with even lower efficiency than could be accounted for by the low uptake. Transformation was not affected by rec-1 and rec-2 mutations in the recipient, and strains cured of the plasmid did not show increased transformation. Plasmid molecules cut once with a restriction enzyme that made blunt ends did not transform. Transformation was favored by the closed circular form of the plasmid.