Spontaneous and Induced Mutation in Mycobacterium avium

Area of Science:

• Microbiology
• Bacterial genetics
• Cell biology

Background:

• Mycobacterium avium presents distinct colonial morphologies: transparent and opaque.
• These variants exhibit differences in cell size and mass composition.

Purpose of the Study:

• To investigate the spontaneous transition rate between M. avium colonial forms.
• To characterize the physical differences between transparent and opaque variants.
• To identify and characterize auxotrophic mutants of M. avium.

Main Methods:

• Monitoring spontaneous transition rates of M. avium B2900 transparent variant to opaque form.
• Comparative analysis of cell morphology and mass (dry weight, protein, DNA, carbohydrate) between variants.
• Induction of auxotrophic mutants using nitrosoguanidine and ultraviolet irradiation.
• Screening for conditional, salt-sensitive mutants.

Main Results:

• The transparent variant of M. avium B2900 transitions to the opaque form at a rate of 4.7 x 10(-5) to 3.5 x 10(-4) per cell per generation.
• Opaque M. avium cells are significantly larger (2-3 times) than transparent cells in terms of dry weight, total protein, DNA, and carbohydrate.
• Conditional, salt-sensitive mutants were successfully induced, with one requiring methionine and tryptophan for growth in high molarity buffer.

Conclusions:

• The transition between M. avium colonial forms is a quantifiable biological process.
• Significant morphological and compositional differences exist between M. avium variants.
• The identification of conditional, salt-sensitive mutants provides tools for further genetic and physiological studies of M. avium.