Résumé
Malonyl-coenzyme A (CoA) is a crucial extender unit for the synthesis of mycolic and other fatty acids in mycobacteria, generated in a reaction catalyzed by acetyl-CoA carboxylase. We previously reported on the essentiality of
accD6
Mtb
encoding the functional acetyl-CoA carboxylase subunit in
Mycobacterium tuberculosis
. Strikingly, the homologous gene in the fast-growing, non-pathogenic
Mycobacterium smegmatis
- (
accD6
Msm
) appeared to be dispensable, and its deletion did not influence the cell lipid content. Herein, we demonstrate that, despite the difference in essentiality,
accD6
Msm
and
accD6
Mtb
encode proteins of convergent catalytic activity
in vivo
. To identify an alternative, AccD6-independent, malonyl-CoA synthesis pathway in
M. smegmatis
, a complex genetic approach combined with lipid analysis was applied to screen all five remaining carboxyltransferase genes (
accD1
-
accD5
) with respect to their involvement in mycolic acid biosynthesis and ability to utilize acetyl-CoA as the substrate for carboxylation. This approach revealed that AccD1
Msm
, AccD2
Msm
and AccD3
Msm
are not essential for mycolic acid biosynthesis. Furthermore, we confirmed
in vivo
the function of AccD4
Msm
as an essential, long-chain acyl-CoA carboxyltransferase, unable to carboxylate short-chain substrate. Finally, our comparative studies unambiguously demonstrated between-species difference in
in vivo
ability of AccD5 carboxyltransferase to utilize acetyl-CoA that influences AccD6 essentiality in pathogenic and non-pathogenic mycobacteria.