Increased Phagocytosis of Mycobacterium marinum Mutants Defective in Lipooligosaccharide Production: A STRUCTURE-ACTIVITY RELATIONSHIP STUDY (original) (raw)

2014, Journal of Biological Chemistry

BACKGROUND: Biosynthesis and functions of Mycobacterium marinum lipooligosaccharides (LOS) remain elusive. RESULTS: M. marinum mutants expressing various LOS profiles were generated and used to infect macrophages and amoebae. CONCLUSION: Deep LOS mutants are more efficiently phagocytosed than those lacking only LOS-IV. SIGNIFICANCE: Three novel biosynthetic genes and the effect of the LOS content in modulating uptake by phagocytes are reported. ________________________________________________________________________________ ABSTRACT Mycobacterium marinum is a waterborne pathogen responsible for tuberculosis-like infections in ectotherms and is an occasional opportunistic human pathogen. In the environment, M. marinum also interacts with amoebae, which may serve as a natural reservoir for this microorganism. However, the description of mycobacterial determinants in the early interaction with macrophages or amoebae remains elusive. Lipooligosaccharides (LOS) are cell surface exposed glycolipids capable to modulate the host immune system, suggesting that they may be involved in the early interactions of M. marinum with macrophages. Herein, we addressed whether LOS composition affects the uptake of M. marinum by professional phagocytes. Mutants with various truncated LOS variants were generated, leading to the identification of several previously uncharacterized biosynthetic genes (wbbL2, MMAR_2321 and MMAR_2331). Biochemical and structural approaches allowed resolving the structures of LOS precursors accumulating in this set of mutants. These strains, with structurally defined LOS profiles, were then used to infect both macrophages and Acanthamoebae. An inverse correlation between LOS completeness and uptake of mycobacteria by phagocytes was found, allowing to propose three mutant classes: class I (papA4), devoid of LOS, highly efficiently phagocytosed; class II, accumulating only early LOS intermediates (wbbL2, MMAR_2331), also efficiently phagocytosed but less than class I mutants; class III, lacking LOS-IV (losA, MMAR_2319 and MMAR_2321), phagocytosed similarly to the control strain. These results indicate that phagocytosis is conditioned by the LOS pattern and that the LOS pathway used by M. marinum in macrophages is conserved during infection of amoebae.