The Polyketide Pks1 Contributes to Biofilm Formation in Mycobacterium tuberculosis

Abstract

Infections caused by biofilms are abundant and highly persistent, displaying phenotypic resistance to high concentrations of antimicrobials and modulating host immune systems. Tuberculosis (TB), caused by Mycobacterium tuberculosis, shares these qualities with biofilm infections. To identify genetic determinants of biofilm formation in M. tuberculosis, we performed a small-scale transposon screen using an in vitro pellicle biofilm assay. We identified five M. tuberculosis mutants that were reproducibly attenuated for biofilm production relative to that of the parent strain H37Rv. One of the most attenuated mutants is interrupted in pks1, a polyketide synthase gene. When fused with pks15, as in some M. tuberculosis isolates, pks1 contributes to synthesis of the immunomodulatory phenolic glycolipids (PGLs). However, in strains such as H37Rv with split pks15 and pks1 loci, PGL is not produced and pks1 has no previously defined role. We showed that pks1 complementation restores biofilm production independently of the known role of pks1 in PGL synthesis. We also assessed the relationship among biofilm formation, the pks15/1 genotype, and M. tuberculosis phylogeography. A global survey of M. tuberculosis clinical isolates revealed surprising sequence variability in the pks15/1 locus and substantial variation in biofilm phenotypes. Our studies identify novel M. tuberculosis genes that contribute to biofilm production, including pks1. In addition, we find that the ability to make pellicle biofilms is common among M. tuberculosis isolates from throughout the world, suggesting that this trait is relevant to TB propagation or persistence.

MmpL11 Protein Transports Mycolic Acid-containing Lipids to the Mycobacterial Cell Wall and Contributes to Biofilm Formation in Mycobacterium smegmatis

“…Biofilm formation in mycobacteria is multifactorial, and the roles of GPLs and free mycolates in biofilm formation by M. smegmatis have been demonstrated (10,11,13,33). Although the role of extracellular lipids in mycobacterial biofilm formation has been established, a recent genetic screen demonstrated that M. tuberculosis biofilm formation also requires a number of additional factors that are not limited to cell wall lipid biosynthesis or transport (37). It is unknown whether homologs of these proteins also play a role in M. smegmatis biofilm formation.…”

Rifampin Resistance Mutations Are Associated with Broad Chemical Remodeling of Mycobacterium tuberculosis

“…However, the extent to which rifampin resistance alters PDIM structures or concentrations or controls remodeling of other biochemical components of the multilayered cell wall remains unknown. Cell wall lipids, particularly cell surface polyketides, interface directly with the host and regulate immunogens that are exposed to the host (14) and have been known to control the permeability of the organism (15)(16)(17)(18) in ways that might affect the transport of other drugs. Also, if these candidate cell wall changes can be reproducibly associated with drug resistance phenotypes, then altered lipids might also function as biochemical markers of the drug-resistant state (19).…”

Genetic Dissection of Mycobacterial Biofilms

“…There are numerous diverse forms, ranging from microcolonies on submerged substrata to pellicles at air–medium interfaces [1–4]. biofilms develop through genetically programmed pathways and harbor phenotypically heterogeneous but genetically clonal populations of constituent cells [5–16]. Microbial biofilms display a variety of behaviors that are not associated with dispersed planktonic growth, including tolerance to environmental and immunological stresses and antibiotic resistance.…”