Biofilm and colony growth creates microenvironments that require coordinated localization and function of cell surface molecules within the membrane. However, the mechanisms by which membrane organization regulates these surface molecules during these biofilm-associated growth are poorly understood, limiting our understanding of how bacteria adapt and survive in multicellular communities. Mycobacterium smegmatis contains an inner membrane domain (IMD) at the subpolar regions of the cell that helps mediate cell envelope synthesis. Prior research has identified ponA2 as critical for de novo formation of distinct plasma membrane domains in planktonic growth. PonA2 is a penicillin-binding protein that catalyzes peptidoglycan synthesis by transglycosylase (TG) and transpeptidase (TP) activities. To investigate the role of PonA2 in membrane domain organization in biofilm and colony growth, wild-type, {Delta}ponA2, the complement strain (cponA2), and catalytic inactive variants of PonA2 (TG-, TP-, and TG-/TP-) were analyzed. The IMD subpolar localization in wild-type was preserved in biofilm and colony growth, indicating that IMD localization is not exclusive to planktonic growth. Both biofilm and colony growth of {Delta}ponA2 showed significant structural deformities compared to wild-type. In contrast, the catalytic inactive mutants produced biofilm and colony structures that resembled wild-type, suggesting that PonA2 has additional noncatalytic functions during multicellular growth. The IMD localization of the catalytic inactive mutants was minimally impacted, suggesting that neither catalytic domain is required for IMD localization in biofilm and colony growth. Together, these findings advance our understanding of the complex mycobacterial membrane biology.
Montero-Gutierrez, B., Bande, J., Kado, T.
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