Characterization of the physiological role of the FabH enzyme in M. smegmatis: impact on lipid biosynthesis and viability.

CROTTA ASIS, A; GRAMAJO, H; GAGO, G; SAVORETTI, F

Congreso; XIII CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2018

SAMIGE

Mycobacterium tuberculosis has a very complex life style. The flexibility in its metabolism allows it to adapt and survive within the infected host. During this process, one of the most affected pathways is lipid metabolism, both in the host and in the pathogen. Despite there is a lot of information about the biosynthesis, structure and biological function of the main lipids present in M. tuberculosis envelope, little is known about the mechanisms that allow the bacteria modulate and adapt the biosynthesis of the components of the cell wall in response to changes in environment. Thus, the study of the processes involved in the regulation of the biosynthesis of lipids in M. tuberculosis represents a crucial step in the comprehension of the physiology and physiopathology of this pathogen, as well as to understand the interaction between the mycobacteria and its environment. The biosynthesis of fatty acids in M. tuberculosis involves two different systems of fatty acid synthases (FAS I and FAS II). Both synthases are involved in the biosynthesis of membrane fatty acids and lipid components of the cell wall, like mycolic acids which are essential for viability and pathogenesis and have to work in a coordinate way to keep lipid homeostasis. These two systems are linked by a beta-ketoacyl-acyl carrier protein synthase III, named FabH, that catalyzes a condensing reaction combining acyl-CoAs produced by FAS I with malonyl-ACP to form beta-ketoacyl-ACP. This product is the substrate of the FAS II system which is elongated to produce the precursors of the mycolic acids. Although FabH has been studied at the biochemical level, there are no genetic analysis that could help to unequivocally establish the physiological role of this enzyme. In this work, using a double recombination event strategy we constructed a mutant strain in the putative gene for FabH in Mycobacterium smegmatis and carried out a physiological characterization. We determine that the putative gen is not essential for growth in the conditions studied. However, the mutant strain presents a longer lag phase in liquid medium 7H9, in approximately 6 hours. Also, the colony morphology is different compared with the wild-type strain. Lipids analysis are being carried out to determine the molecular basis of these phenotypes. Our results will help to better understand lipid metabolism and regulation of this organism.