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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Disclosures
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

A protocol is presented to extract the total lipid content of the cell wall of a wide range of mycobacteria. Moreover, extraction and analytical protocols of the different types of mycolic acids are shown. A thin-layer chromatographic protocol to monitor these mycobacterial compounds is also provided.

Abstract

Mycobacteria species can differ from one another in the rate of growth, presence of pigmentation, the colony morphology displayed on solid media, as well as other phenotypic characteristics. However, they all have in common the most relevant character of mycobacteria: its unique and highly hydrophobic cell wall. Mycobacteria species contain a membrane-covalent linked complex that includes arabinogalactan, peptidoglycan, and long-chains of mycolic acids with types that differ between mycobacteria species. Additionally, mycobacteria can also produce lipids that are located, non-covalently linked, on their cell surfaces, such as phthiocerol dimycocerosates (PDIM), phenolic glycolipids (PGL), glycopeptidolipids (GPL), acyltrehaloses (AT), or phosphatidil-inositol mannosides (PIM), among others. Some of them are considered virulence factors in pathogenic mycobacteria, or critical antigenic lipids in host-mycobacteria interaction. For these reasons, there is a significant interest in the study of mycobacterial lipids due to their application in several fields, from understanding their role in the pathogenicity of mycobacteria infections, to a possible implication as immunomodulatory agents for the treatment of infectious diseases and other pathologies such as cancer. Here, a simple approach to extract and analyze the total lipid content and the mycolic acid composition of mycobacteria cells grown in a solid medium using mixtures of organic solvents is presented. Once the lipid extracts are obtained, thin-layer chromatography (TLC) is performed to monitor the extracted compounds. The example experiment is performed with four different mycobacteria: the environmental fast-growing Mycolicibacterium brumae and Mycolicibacterium fortuitum, the attenuated slow-growing Mycobacterium bovis bacillus Calmette-Guérin (BCG), and the opportunistic pathogen fast-growing Mycobacterium abscessus, demonstrating that methods shown in the present protocol can be used to a wide range of mycobacteria.

Introduction

Mycobacterium is a genus that comprises pathogenic and non-pathogenic species, characterized by having a highly hydrophobic and impermeable cell wall formed by their peculiar lipids. Specifically, the mycobacterial cell wall contains mycolic acids, which are α-alkyl and β-hydroxy fatty acids, in which the α-branch is constant in all mycolic acids (except for the length) and the β-chain, called the meromycolate chain, is a long aliphatic chain that may contain different functional chemical groups described along with the literature (α-, α'-, methoxy-, κ-, epoxy-, carboxy-, and ω-1-methoxy- mycolates), therefore produ....

Protocol

1. Extraction of the total non-covalent-linked lipids from mycobacteria (Figure 1)

  1. Scratch 0.2 g of mycobacteria from a solid media and add to a glass tube with a polytetrafluoroethlene (PTFE) liner screw caps. Add a solution consisting of 5 mL of chloroform and 10 mL of methanol (chloroform:methanol, 1:2).
    NOTE: When organic solvents are used, only glass recipient should be used. No plastic containers are allowed. Moreover, PTFE liner screw caps for bottles are needed.
    CAUTION: Chloroform is a potentially toxic and extremely hazardous substance. It must be used in a laminar flow hood wearing appropriate personal....

Representative Results

With the aim of showing a wide range of lipids present in different mycobacteria species, M. bovis BCG was selected as it is rough and slow-growing mycobacteria. The rough and fast-growing M. fortuitum and M. brumae were added in the procedure and, finally, the smooth morphotype of M. abscessus was also included. These four species permit us to visualize a broad spectrum of mycobacteria-derived lipids such as acyltrehaloses (AT), GPLs, PDIM, PGL, PIM, TDM, and TMM. Moreover, all four s.......

Discussion

A simple protocol considered as the gold standard method for the extraction of noncovalently linked lipid compounds from the mycobacterial cell wall is presented. Further visualization by one- and two-dimensional TLCs from the extracted lipids of four different mycobacteria is shown.

Two consecutive combined mixtures of chloroform and methanol to recover the lipidic content of mycobacterial cells is the most widely used solvent mixture23,24<.......

Disclosures

The authors have nothing to disclose.

Acknowledgements

This research was funded by the Spanish Ministry of Science, Innovation and Universities (RTI2018-098777-B-I00), the FEDER Funds, and the Generalitat of Catalunya (2017SGR-229). Sandra Guallar-Garrido is the recipient of a PhD contract (FI) from the Generalitat de Catalunya.

....

Materials

NameCompanyCatalog NumberComments
Acetic AcidMerck100063CAUTION. Anhydrous for analysis EMSURE® ACS,ISO,Reag. Ph Eur
AcetoneCarlo Erba400971NCAUTION. ACETONE RPE-ACS-ISO FOR ANALYS ml 1000
AnthroneMerck8014610010Anthrone for synthesis.
BenzeneCarlo Erba426113CAUTION. Benzene RPE - For analysis - ACS 2.5 l
Capillary glass tubeMerckBR708709BRAND® disposable BLAUBRAND® micropipettes, intraMark
ChloroformCarlo Erba412653CAUTION. Chloroform RS - For HPLC - Isocratic grade - Stabilized with ethanol 2.5 L
Dry block heaterJ.P. Selecta7471200
DicloromethaneCarlo Erba412622CAUTION. Dichloromethane RS - For HPLC - Isocratic grade - Stabilized with amylene 2.5 L
Diethyl etherCarlo Erba412672CAUTION. Diethyl ether RS - For HPLC - Isocratic grade - Not stabilized 2.5 L
Ethyl AcetatePanreac1313181211CAUTION. Ethyl acetate (Reag. USP, Ph. Eur.) for analysis, ACS, ISO
Ethyl Alcohol AbsoluteCarlo Erba4146072CAUTION. Ethanol absolute anhydrous RPE - For analysis - ACS - Reag. Ph.Eur. - Reag. USP 1 L
Glass funnelVidraFOCDURA.2133148 1217/1
Glass tubeVidraFOCVFOC.45066A-16125Glass tube with PTFE recovered cap
MethanolCarlo Erba412722CAUTION. Methanol RS - For HPLC - GOLD - Ultragradient grade 2.5 L
Molybdatophosphoric acid hydrateMerck51429-74-4CAUTION.
Molybdenum Blue Spray Reagent, 1.3%SigmaM1942-100MLCAUTION.
n-hexaneCarlo Erba446903CAUTION. n-Hexane 99% RS - ATRASOL - For traces analysis 2.5 L
n-nitroso-n-methylureaSigmaN4766CAUTION
Orbital shaking platformDDBiolab995018NB-205L benchtop shaking incubator
Petroleum ether (60-80ºC)Carlo Erba427003CAUTION. Petroleum ether 60 - 80°C RPE - For analysis 2.5 L
SprayerVidraFOC712/1
Sodium sulphate anhydrousMerck238597
Sulfuric acid 95-97%Merck1007311000CAUTION. Sulfuric acid 95-97%
TLC chamberMerckZ204226-1EARectangular TLC developing tanks, complete L × H × W 22 cm × 22 cm × 10 cm
TLC plateMerck1057210001TLC SilicaGel 60- 20x20 cm x 25 u
TLC Plate HeaterCAMAG223306CAMAG TLC Plat Heater III
TolueneCarlo Erba488551CAUTION. Toluene RPE - For analysis - ISO - ACS - Reag.Ph.Eur. - Reag.USP 1 L
VortexFisher Scientific10132562IKA Agitador IKA vórtex 3
1-naphtholSigma-Aldrich102269427CAUTION.

References

  1. Watanabe, M., et al. Location of functional groups in mycobacterial meromycolate chains; the recognition of new structural principles in mycolic acids. Microbiology. 148 (6), 1881-1902 (2002).
  2. Global Health Organization World Health Organization.

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MycobacteriaLipidsThin Layer ChromatographyExtractionChloroformMethanolMycolic AcidN hexaneTLC

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