The biology of environmental mycobacteria

Although the environmental mycobacteria are slow growing relative to other microorganisms in water and soil which would suggest that they are poor competitors, compensating factors permit survival, growth and persistence in natural and human-engineered environments. Factors such as the hydrophobic, lipid-rich impermeable envelope, biofilm formation, acid resistance, anaerobic survival and metabolism of recalcitrant carbon compounds permit survival and growth of the environmental mycobacteria in a wide range of natural and human-engineered habitats. High numbers of environmental mycobacteria are found in coastal swamps and estuaries and boreal, peat-rich forest soils and waters. The hydrophobic surface results in concentration of the environmental mycobacteria at interfaces (air-water and surface-water) and in aerosolized droplets ejected from water. The survival and growth in protozoa and amoebae permit environmental mycobacteria to persist in habitats subject to predation and likely led to survival and growth in phagocytic cells of animals. Finally, slow growth allows time for mycobacterial cells to adapt to changing conditions before loss of viability.