The porin MspA from Mycobacterium smegmatis improves growth of Mycobacterium bovis BCG.

Mycobacteria are characterized by an extremely thick hydrophobic cell wall restricting the permeability for small hydrophilic compounds. Recently, a new efficient porin (MspA) has been identified in Mycobacterium smegmatis, which is lacking in slow-growing mycobacteria. Since we were interested in investigating the influence of porins on growth of slow-growing Mycobacterium bovis BCG, we inserted a 3429 bp DNA fragment from M. smegmatis carrying the mspA gene in an integrative vector and transferred it into M. bovis BCG. Expression of mspA in the BCG derivative was shown by RT-PCR and Western blot. Quantification of bacterial growth on agar plates demonstrated two- to four-fold better growth of the BCG derivative with the transferred DNA compared with the reference strain. Transposon mutagenesis proved the mspA gene to be responsible for the growth enhancement. Intracellular multiplication of the BCG derivative in the mouse macrophage cell line J774 and the human pneumocyte cell line A549 was also clearly enhanced pointing to a possible role of porins in the interaction of mycobacteria with their hosts.