THE EFFECT OF OXYGENATED MYCOLIC ACID COMPOSITION ON CELL-WALL FUNCTION AND MACROPHAGE GROWTH IN MYCOBACTERIUM-TUBERCULOSIS

There are three major structural classes of mycolic acids in the cell envelope of Mycobacterium tuberculosis (MTB): alpha-, methoxy- and ket omycolate. The two oxygen-containing classes are biosynthetically rela ted through a common cu-methyl hydroxymycolate intermediate. BCG strai ns that fail to produce methoxymycolate and instead produce only keto- and alpha-mycolic acids show apparent defects in the O-methyltransfer ase MMAS-3. Overproduction of MMAS-3 from MTB resulted in a complete r eplacement of ketomycolate by methoxymycolate in both BCG and MTB. In vitro growth of these recombinant strains lacking ketomycolate was imp aired at reduced temperatures but appeared to be normal at 37 degrees C. Glucose uptake was significantly decreased in such strains, but upt ake of chenodeoxycholate and glycine was unaffected. Although sensitiv ity to INH remained unchanged, these cells were found to be hypersensi tive to ampicillin and rifampicin. Infectivity of BCG and H37Rv wild t ype or MMAS-3 overproducers in THP-1 cells was somewhat affected, but the ability of the strains lacking ketomycolate to grow within this ma crophage-like cell line was severely compromised. In vivo labelling of mycolic acids during growth of H37Rv within THP-1 cells revealed a su bstantial increase in ketomycolate and alphamycolate synthesized by in tracellularly grown mycobacteria. These results establish a critical r ole for mycolate composition in proper cell wall function during the g rowth of MTB in vivo.