title: Inverse correlation between salt tolerance and host-adaptation in mycobacteria.
abstract: BACKGROUND
  The genus Mycobacterium includes host-adapted organisms regarded as obligate and opportunistic pathogens and environmental organisms. Factors contributing to this wide range of adaptations are poorly known.
  
  
  RESULTS
  We studied the salt tolerance of 46 Mycobacterium species of medical interest. Representative strains of the Mycobacterium tuberculosis complex, Mycobacterium avium complex, Mycobacterium chelonae-abscessus complex, Mycobacterium ulcerans, Mycobacterium marinum, Mycobacterium lentiflavum, Mycobacterium fortuitum and Mycobacterium conceptionense were inoculated on Middlebrook 7H10 medium supplemented with 0-10% sodium chloride. Colonies were counted after 2-4 week incubation at the appropriate 30-37 °C temperature depending on the tested strain. Further comparative genomics was done on 15 Mycobacterium strains representing the spectrum of salt-tolerance of mycobacteria. Based on the results the different species were grouped according to their salt tolerance into a "salt-sensitive" group (growth up to ≤3% salt) containing the M. tuberculosis complex, Mycobacterium chelonae, Mycobacterium lentiflavum, Mycobacterium ulcerans and Mycobacterium marinum; a "salt-intermediate" group (growth between 4 and 6% salt) comprising Mycobacterium avium, Mycobacterium intracellulare, Mycobacterium chimaera and a "salt-resistant" group (growth up to >6%) comprising Mycobacterium homonissuis, Mycobacterium bolettii, Mycobacterium fortuitum and Mycobacterium conceptionense. Genomic analysis revealed that 290 genes were unique to species belonging to the salt-sensitive group; and that 15% were annotated as being functionally associated with the ESX secretion systems Pro-Glu and Pro-Pro-Glu family proteins.
  
  
  CONCLUSIONS
  In this work we found an inverse correlation between salt tolerance and host adaptation. We thus propose that salinity is one of the multiple factors determining the ecological niches of mycobacteria.
authors.affiliation: Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, CNRS, UMR 7278, IRD 198, Faculté de Médecine, Aix-Marseille Université, 27, Boulevard Jean Moulin, 13385, Marseille Cedex 5, France.
authors.forename: Shady
authors.initials: S
authors.lastname: Asmar
authors.affiliation: Université de Rennes 1, Rennes, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Sassi
authors.affiliation: Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, CNRS, UMR 7278, IRD 198, Faculté de Médecine, Aix-Marseille Université, 27, Boulevard Jean Moulin, 13385, Marseille Cedex 5, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Phelippeau
authors.affiliation: Unité de Recherche sur les Maladies Infectieuses et Tropicales Emergentes, CNRS, UMR 7278, IRD 198, Faculté de Médecine, Aix-Marseille Université, 27, Boulevard Jean Moulin, 13385, Marseille Cedex 5, France. Michel.Drancourt@univ-amu.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Drancourt
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics; D001431:Bacteriological Techniques / Q000379:methods; D016000:Cluster Analysis; D004783:Environmental Microbiology; D005798:Genes, Bacterial / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics; D054884:Host-Pathogen Interactions; D006801:Humans; D009161:Mycobacterium / Q000145:classification / Q000235:genetics / Q000502:physiology*; D009164:Mycobacterium Infections / Q000382:microbiology*; D055049:Salt Tolerance / Q000235:genetics / Q000502:physiology*; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins
keywords: Culture; Mycobacterium; Mycobacterium canettii; Mycobacterium tuberculosis; Salt